8088 8-BIT HMOS MICROPROCESSOR 8088/8088-2 Y 8-Bit Data Bus Interface Y Byte, Word, and Block Operations Y 16-Bit Internal Architecture Y Y Direct Addressing Capability to 1 Mbyte of Memory 8-Bit and 16-Bit Signed and Unsigned Arithmetic in Binary or Decimal, Including Multiply and Divide Direct Software Compatibility with 8086 CPU Y Y Y 14-Word by 16-Bit Register Set with Symmetrical Operations Two Clock Rates: Ð 5 MHz for 8088 Ð 8 MHz for 8088-2 Y Available in EXPRESS Ð Standard Temperature Range Ð Extended Temperature Range Y 24 Operand Addressing Modes The Intel 8088 is a high performance microprocessor implemented in N-channel, depletion load, silicon gate technology (HMOS-II), and packaged in a 40-pin CERDIP package. The processor has attributes of both 8and 16-bit microprocessors. It is directly compatible with 8086 software and 8080/8085 hardware and peripherals. 231456 – 2 231456 – 1 Figure 2. 8088 Pin Configuration Figure 1. 8088 CPU Functional Block Diagram August 1990 Order Number: 231456-006 8088 Table 1. Pin Description The following pin function descriptions are for 8088 systems in either minimum or maximum mode. The ‘‘local bus’’ in these descriptions is the direct multiplexed bus interface connection to the 8088 (without regard to additional bus buffers). Symbol Pin No. Type Name and Function AD7–AD0 9–16 I/O ADDRESS DATA BUS: These lines constitute the time multiplexed memory/IO address (T1) and data (T2, T3, Tw, T4) bus. These lines are active HIGH and float to 3-state OFF during interrupt acknowledge and local bus ‘‘hold acknowledge’’. A15–A8 2–8, 39 O ADDRESS BUS: These lines provide address bits 8 through 15 for the entire bus cycle (T1 – T4). These lines do not have to be latched by ALE to remain valid. A15 – A8 are active HIGH and float to 3-state OFF during interrupt acknowledge and local bus ‘‘hold acknowledge’’. A19/S6, A18/S5, 35–38 O ADDRESS/STATUS: During T1, these are the four most significant A17/S4, A16/S3 address lines for memory operations. During I/O operations, these lines are LOW. During memory and I/O operations, status information is available on these lines during T2, T3, Tw, and T4. S6 is always low. The status of the interrupt enable flag bit (S5) is updated at the beginning of each clock cycle. S4 and S3 are encoded as shown. This information indicates which segment register is presently being used for data accessing. These lines float to 3-state OFF during local bus ‘‘hold acknowledge’’. S4 S3 Characteristics 0 (LOW) 0 Alternate Data 0 1 Stack 1 (HIGH) 0 Code or None 1 1 Data S6 is 0 (LOW) RD 32 O READ: Read strobe indicates that the processor is performing a memory or I/O read cycle, depending on the state of the IO/M pin or S2. This signal is used to read devices which reside on the 8088 local bus. RD is active LOW during T2, T3 and Tw of any read cycle, and is guaranteed to remain HIGH in T2 until the 8088 local bus has floated. This signal floats to 3-state OFF in ‘‘hold acknowledge’’. READY 22 I READY: is the acknowledgement from the addressed memory or I/O device that it will complete the data transfer. The RDY signal from memory or I/O is synchronized by the 8284 clock generator to form READY. This signal is active HIGH. The 8088 READY input is not synchronized. Correct operation is not guaranteed if the set up and hold times are not met. INTR 18 I INTERRUPT REQUEST: is a level triggered input which is sampled during the last clock cycle of each instruction to determine if the processor should enter into an interrupt acknowledge operation. A subroutine is vectored to via an interrupt vector lookup table located in system memory. It can be internally masked by software resetting the interrupt enable bit. INTR is internally synchronized. This signal is active HIGH. TEST 23 I TEST: input is examined by the ‘‘wait for test’’ instruction. If the TEST input is LOW, execution continues, otherwise the processor waits in an ‘‘idle’’ state. This input is synchronized internally during each clock cycle on the leading edge of CLK. 2 8088 Table 1. Pin Description (Continued) Symbol NMI Pin No. 17 Type I Name and Function NON-MASKABLE INTERRUPT: is an edge triggered input which causes a type 2 interrupt. A subroutine is vectored to via an interrupt vector lookup table located in system memory. NMI is not maskable internally by software. A transition from a LOW to HIGH initiates the interrupt at the end of the current instruction. This input is internally synchronized. RESET 21 I RESET: causes the processor to immediately terminate its present activity. The signal must be active HIGH for at least four clock cycles. It restarts execution, as described in the instruction set description, when RESET returns LOW. RESET is internally synchronized. CLK 19 I CLOCK: provides the basic timing for the processor and bus controller. It is asymmetric with a 33% duty cycle to provide optimized internal timing. VCC: is the a 5V g 10% power supply pin. VCC GND MN/MX 40 1, 20 33 I GND: are the ground pins. MINIMUM/MAXIMUM: indicates what mode the processor is to operate in. The two modes are discussed in the following sections. The following pin function descriptions are for the 8088 minimum mode (i.e., MN/MX e VCC). Only the pin functions which are unique to minimum mode are described; all other pin functions are as described above. Symbol Pin No. Type Name and Function IO/M 28 O STATUS LINE: is an inverted maximum mode S2. It is used to distinguish a memory access from an I/O access. IO/M becomes valid in the T4 preceding a bus cycle and remains valid until the final T4 of the cycle (I/O e HIGH, M e LOW). IO/M floats to 3-state OFF in local bus ‘‘hold acknowledge’’. WR 29 O WRITE: strobe indicates that the processor is performing a write memory or write I/O cycle, depending on the state of the IO/M signal. WR is active for T2, T3, and Tw of any write cycle. It is active LOW, and floats to 3-state OFF in local bus ‘‘hold acknowledge’’. INTA 24 O INTA: is used as a read strobe for interrupt acknowledge cycles. It is active LOW during T2, T3, and Tw of each interrupt acknowledge cycle. ALE 25 O ADDRESS LATCH ENABLE: is provided by the processor to latch the address into an address latch. It is a HIGH pulse active during clock low of T1 of any bus cycle. Note that ALE is never floated. DT/R 27 O DATA TRANSMIT/RECEIVE: is needed in a minimum system that desires to use a data bus transceiver. It is used to control the direction of data flow through the transceiver. Logically, DT/R is equivalent to S1 in the maximum mode, and its timing is the same as for IO/M (T e HIGH, R e LOW). This signal floats to 3-state OFF in local ‘‘hold acknowledge’’. DEN 26 O DATA ENABLE: is provided as an output enable for the data bus transceiver in a minimum system which uses the transceiver. DEN is active LOW during each memory and I/O access, and for INTA cycles. For a read or INTA cycle, it is active from the middle of T2 until the middle of T4, while for a write cycle, it is active from the beginning of T2 until the middle of T4. DEN floats to 3-state OFF during local bus ‘‘hold acknowledge’’. 3 8088 Table 1. Pin Description (Continued) Symbol Pin No. Type Name and Function HOLD, 31, 30 I, O HOLD: indicates that another master is requesting a local bus ‘‘hold’’. To be HLDA acknowledged, HOLD must be active HIGH. The processor receiving the ‘‘hold’’ request will issue HLDA (HIGH) as an acknowledgement, in the middle of a T4 or Ti clock cycle. Simultaneous with the issuance of HLDA the processor will float the local bus and control lines. After HOLD is detected as being LOW, the processor lowers HLDA, and when the processor needs to run another cycle, it will again drive the local bus and control lines. HOLD and HLDA have internal pull-up resistors. Hold is not an asynchronous input. External synchronization should be provided if the system cannot otherwise guarantee the set up time. SSO 34 O STATUS LINE: is logically equivalent to SO in the maximum mode. The combination of SSO, IO/M and DT/R allows the system to completely decode the current bus cycle status. IO/M 1(HIGH) 1 1 1 0(LOW) 0 0 0 DT/R SSO 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 Characteristics Interrupt Acknowledge Read I/O Port Write I/O Port Halt Code Access Read Memory Write Memory Passive The following pin function descriptions are for the 8088/8288 system in maximum mode (i.e., MN/MX e GND). Only the pin functions which are unique to maximum mode are described; all other pin functions are as described above. Symbol Pin No. Type Name and Function S2, S1, S0 26–28 O STATUS: is active during clock high of T4, T1, and T2, and is returned to the passive state (1,1,1) during T3 or during Tw when READY is HIGH. This status is used by the 8288 bus controller to generate all memory and I/O access control signals. Any change by S2, S1, or S0 during T4 is used to indicate the beginning of a bus cycle, and the return to the passive state in T3 and Tw is used to indicate the end of a bus cycle. These signals float to 3-state OFF during ‘‘hold acknowledge’’. During the first clock cycle after RESET becomes active, these signals are active HIGH. After this first clock, they float to 3-state OFF. S2 S1 S0 Characteristics 0(LOW) 0 0 Interrupt Acknowledge 0 0 1 Read I/O Port 0 1 0 Write I/O Port 0 1 1 Halt 1(HIGH) 0 0 Code Access 1 0 1 Read Memory 1 1 0 Write Memory 1 1 1 Passive 4 8088 Table 1. Pin Description (Continued) Symbol RQ/GT0, RQ/GT1 LOCK QS1, QS0 Pin No. 30, 31 Type I/O Name and Function REQUEST/GRANT: pins are used by other local bus masters to force the processor to release the local bus at the end of the processor’s current bus cycle. Each pin is bidirectional with RQ/GT0 having higher priority than RQ/ GT1. RQ/GT has an internal pull-up resistor, so may be left unconnected. The request/grant sequence is as follows (See Figure 8): 1. A pulse of one CLK wide from another local bus master indicates a local bus request (‘‘hold’’) to the 8088 (pulse 1). 2. During a T4 or TI clock cycle, a pulse one clock wide from the 8088 to the requesting master (pulse 2), indicates that the 8088 has allowed the local bus to float and that it will enter the ‘‘hold acknowledge’’ state at the next CLK. The CPU’s bus interface unit is disconnected logically from the local bus during ‘‘hold acknowledge’’. The same rules as for HOLD/HOLDA apply as for when the bus is released. 3. A pulse one CLK wide from the requesting master indicates to the 8088 (pulse 3) that the ‘‘hold’’ request is about to end and that the 8088 can reclaim the local bus at the next CLK. The CPU then enters T4. Each master-master exchange of the local bus is a sequence of three pulses. There must be one idle CLK cycle after each bus exchange. Pulses are active LOW. If the request is made while the CPU is performing a memory cycle, it will release the local bus during T4 of the cycle when all the following conditions are met: 1. Request occurs on or before T2. 2. Current cycle is not the low bit of a word. 3. Current cycle is not the first acknowledge of an interrupt acknowledge sequence. 4. A locked instruction is not currently executing. If the local bus is idle when the request is made the two possible events will follow: 1. Local bus will be released during the next clock. 2. A memory cycle will start within 3 clocks. Now the four rules for a currently active memory cycle apply with condition number 1 already satisfied. 29 O LOCK: indicates that other system bus masters are not to gain control of the system bus while LOCK is active (LOW). The LOCK signal is activated by the ‘‘LOCK’’ prefix instruction and remains active until the completion of the next instruction. This signal is active LOW, and floats to 3-state off in ‘‘hold acknowledge’’. 24, 25 O QUEUE STATUS: provide status to allow external tracking of the internal 8088 instruction queue. The queue status is valid during the CLK cycle after which the queue operation is performed. QS1 0(LOW) 0 1(HIGH) 1 Ð 34 O QS0 0 1 0 1 Characteristics No Operation First Byte of Opcode from Queue Empty the Queue Subsequent Byte from Queue Pin 34 is always high in the maximum mode. 5 8088 231456 – 3 Figure 3. Memory Organization FUNCTIONAL DESCRIPTION Memory Organization The processor provides a 20-bit address to memory which locates the byte being referenced. The memory is organized as a linear array of up to 1 million bytes, addressed as 00000(H) to FFFFF(H). The memory is logically divided into code, data, extra data, and stack segments of up to 64K bytes each, with each segment falling on 16-byte boundaries (See Figure 3). All memory references are made relative to base addresses contained in high speed segment registers. The segment types were chosen based on the adMemory Reference Used 6 Segment Register Used dressing needs of programs. The segment register to be selected is automatically chosen according to the rules of the following table. All information in one segment type share the same logical attributes (e.g. code or data). By structuring memory into relocatable areas of similar characteristics and by automatically selecting segment registers, programs are shorter, faster, and more structured. Word (16-bit) operands can be located on even or odd address boundaries. For address and data operands, the least significant byte of the word is stored in the lower valued address location and the most significant byte in the next higher address location. The BIU will automatically execute two fetch or write cycles for 16-bit operands. Segment Selection Rule Instructions CODE (CS) Automatic with all instruction prefetch. Stack STACK (SS) All stack pushes and pops. Memory references relative to BP base register except data references. Local Data DATA (DS) Data references when: relative to stack, destination of string operation, or explicity overridden. External (Global) Data EXTRA (ES) Destination of string operations: Explicitly selected using a segment override. 8088 Certain locations in memory are reserved for specific CPU operations (See Figure 4). Locations from addresses FFFF0H through FFFFFH are reserved for operations including a jump to the initial system initialization routine. Following RESET, the CPU will always begin execution at location FFFF0H where the jump must be located. Locations 00000H through 003FFH are reserved for interrupt operations. Fourbyte pointers consisting of a 16-bit segment address and a 16-bit offset address direct program flow to one of the 256 possible interrupt service routines. The pointer elements are assumed to have been stored at their respective places in reserved memory prior to the occurrence of interrupts. figuration. The definition of a certain subset of the pins changes, dependent on the condition of the strap pin. When the MN/MX pin is strapped to GND, the 8088 defines pins 24 through 31 and 34 in maximum mode. When the MN/MX pin is strapped to VCC, the 8088 generates bus control signals itself on pins 24 through 31 and 34. Minimum and Maximum Modes The demultiplexed mode requires one latch (for 64K addressability) or two latches (for a full megabyte of addressing). A third latch can be used for buffering if the address bus loading requires it. A transceiver can also be used if data bus buffering is required (See Figure 6). The 8088 provides DEN and DT/R to control the transceiver, and ALE to latch the addresses. This configuration of the minimum mode provides the standard demultiplexed bus structure with heavy bus buffering and relaxed bus timing requirements. The requirements for supporting minimum and maximum 8088 systems are sufficiently different that they cannot be done efficiently with 40 uniquely defined pins. Consequently, the 8088 is equipped with a strap pin (MN/MX) which defines the system con- The minimum mode 8088 can be used with either a multiplexed or demultiplexed bus. The multiplexed bus configuration is compatible with the MCS-85 multiplexed bus peripherals. This configuration (See Figure 5) provides the user with a minimum chip count system. This architecture provides the 8088 processing power in a highly integrated form. The maximum mode employs the 8288 bus controller (See Figure 7). The 8288 decodes status lines S0, S1, and S2, and provides the system with all bus control signals. Moving the bus control to the 8288 provides better source and sink current capability to the control lines, and frees the 8088 pins for extended large system features. Hardware lock, queue status, and two request/grant interfaces are provided by the 8088 in maximum mode. These features allow co-processors in local bus and remote bus configurations. 231456 – 4 Figure 4. Reserved Memory Locations 7 8088 231456 – 5 Figure 5. Multiplexed Bus Configuration 8 8088 231456 – 6 Figure 6. Demultiplexed Bus Configuration 231456 – 7 Figure 7. Fully Buffered System Using Bus Controller 9 8088 Bus Operation The 8088 address/data bus is broken into three partsÐthe lower eight address/data bits (AD0 – AD7), the middle eight address bits (A8–A15), and the upper four address bits (A16–A19). The address/data bits and the highest four address bits are time multiplexed. This technique provides the most efficient use of pins on the processor, permitting the use of a standard 40 lead package. The middle eight address bits are not multiplexed, i.e. they remain val- id throughout each bus cycle. In addition, the bus can be demultiplexed at the processor with a single address latch if a standard, non-multiplexed bus is desired for the system. Each processor bus cycle consists of at least four CLK cycles. These are referred to as T1, T2, T3, and T4 (See Figure 8). The address is emitted from the processor during T1 and data transfer occurs on the bus during T3 and T4. T2 is used primarily for chang- 231456 – 8 Figure 8. Basic System Timing 10 8088 ing the direction of the bus during read operations. In the event that a ‘‘NOT READY’’ indication is given by the addressed device, ‘‘wait’’ states (Tw) are inserted between T3 and T4. Each inserted ‘‘wait’’ state is of the same duration as a CLK cycle. Periods can occur between 8088 driven bus cycles. These are referred to as ‘‘idle’’ states (Ti), or inactive CLK cycles. The processor uses these cycles for internal housekeeping. During T1 of any bus cycle, the ALE (address latch enable) signal is emitted (by either the processor or the 8288 bus controller, depending on the MN/MX strap). At the trailing edge of this pulse, a valid address and certain status information for the cycle may be latched. which use register DX as a pointer, have full address capability, while the direct I/O instructions directly address one or two of the 256 I/O byte locations in page 0 of the I/O address space. I/O ports are addressed in the same manner as memory locations. Designers familiar with the 8085 or upgrading an 8085 design should note that the 8085 addresses I/O with an 8-bit address on both halves of the 16bit address bus. The 8088 uses a full 16-bit address on its lower 16 address lines. EXTERNAL INTERFACE Processor Reset and Initialization Status bits S0, S1, and S2 are used by the bus controller, in maximum mode, to identify the type of bus transaction according to the following table: S2 S1 S0 Characteristics 0(LOW) 0 0 0 1(HIGH) 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 Interrupt Acknowledge Read I/O Write I/O Halt Instruction Fetch Read Data from Memory Write Data to Memory Passive (No Bus Cycle) Status bits S3 through S6 are multiplexed with high order address bits and are therefore valid during T2 through T4. S3 and S4 indicate which segment register was used for this bus cycle in forming the address according to the following table: Processor initialization or start up is accomplished with activation (HIGH) of the RESET pin. The 8088 RESET is required to be HIGH for greater than four clock cycles. The 8088 will terminate operations on the high-going edge of RESET and will remain dormant as long as RESET is HIGH. The low-going transition of RESET triggers an internal reset sequence for approximately 7 clock cycles. After this interval the 8088 operates normally, beginning with the instruction in absolute locations FFFF0H (See Figure 4). The RESET input is internally synchronized to the processor clock. At initialization, the HIGH to LOW transition of RESET must occur no sooner than 50 ms after power up, to allow complete initialization of the 8088. S4 S3 Characteristics NMI asserted prior to the 2nd clock after the end of RESET will not be honored. If NMI is asserted after that point and during the internal reset sequence, the processor may execute one instruction before responding to the interrupt. A hold request active immediately after RESET will be honored before the first instruction fetch. 0(LOW) 0 1(HIGH) 1 0 1 0 1 Alternate Data (Extra Segment) Stack Code or None Data All 3-state outputs float to 3-state OFF during RESET. Status is active in the idle state for the first clock after RESET becomes active and then floats to 3-state OFF. ALE and HLDA are driven low. S5 is a reflection of the PSW interrupt enable bit. S6 is always equal to 0. I/O Addressing In the 8088, I/O operations can address up to a maximum of 64K I/O registers. The I/O address appears in the same format as the memory address on bus lines A15–A0. The address lines A19–A16 are zero in I/O operations. The variable I/O instructions, Interrupt Operations Interrupt operations fall into two classes: software or hardware initiated. The software initiated interrupts and software aspects of hardware interrupts are specified in the instruction set description in the iAPX 88 book or the iAPX 86,88 User’s Manual. Hardware interrupts can be classified as nonmaskable or maskable. 11 8088 Interrupts result in a transfer of control to a new program location. A 256 element table containing address pointers to the interrupt service program locations resides in absolute locations 0 through 3FFH (See Figure 4), which are reserved for this purpose. Each element in the table is 4 bytes in size and corresponds to an interrupt ‘‘type.’’ An interrupting device supplies an 8-bit type number, during the interrupt acknowledge sequence, which is used to vector through the appropriate element to the new interrupt service program location. Non-Maskable Interrupt (NMI) The processor provides a single non-maskable interrupt (NMI) pin which has higher priority than the maskable interrupt request (INTR) pin. A typical use would be to activate a power failure routine. The NMI is edge-triggered on a LOW to HIGH transition. The activation of this pin causes a type 2 interrupt. enable bit will be zero unless specifically set by an instruction. During the response sequence (See Figure 9), the processor executes two successive (back to back) interrupt acknowledge cycles. The 8088 emits the LOCK signal (maximum mode only) from T2 of the first bus cycle until T2 of the second. A local bus ‘‘hold’’ request will not be honored until the end of the second bus cycle. In the second bus cycle, a byte is fetched from the external interrupt system (e.g., 8259A PIC) which identifies the source (type) of the interrupt. This byte is multiplied by four and used as a pointer into the interrupt vector lookup table. An INTR signal left HIGH will be continually responded to within the limitations of the enable bit and sample period. The interrupt return instruction includes a flags pop which returns the status of the original interrupt enable bit when it restores the flags. NMI is required to have a duration in the HIGH state of greater than two clock cycles, but is not required to be synchronized to the clock. Any higher going transition of NMI is latched on-chip and will be serviced at the end of the current instruction or between whole moves (2 bytes in the case of word moves) of a block type instruction. Worst case response to NMI would be for multiply, divide, and variable shift instructions. There is no specification on the occurrence of the low-going edge; it may occur before, during, or after the servicing of NMI. Another highgoing edge triggers another response if it occurs after the start of the NMI procedure. The signal must be free of logical spikes in general and be free of bounces on the low-going edge to avoid triggering extraneous responses. HALT Maskable Interrupt (INTR) Read/Modify/Write (Semaphore) Operations via LOCK The 8088 provides a single interrupt request input (INTR) which can be masked internally by software with the resetting of the interrupt enable (IF) flag bit. The interrupt request signal is level triggered. It is internally synchronized during each clock cycle on the high-going edge of CLK. To be responded to, INTR must be present (HIGH) during the clock period preceding the end of the current instruction or the end of a whole move for a block type instruction. During interrupt response sequence, further interrupts are disabled. The enable bit is reset as part of the response to any interrupt (INTR, NMI, software interrupt, or single step), although the FLAGS register which is automatically pushed onto the stack reflects the state of the processor prior to the interrupt. Until the old FLAGS register is restored, the 12 When a software HALT instruction is executed, the processor indicates that it is entering the HALT state in one of two ways, depending upon which mode is strapped. In minimum mode, the processor issues ALE, delayed by one clock cycle, to allow the system to latch the halt status. Halt status is available on IO/M, DT/R, and SSO. In maximum mode, the processor issues appropriate HALT status on S2, S1, and S0, and the 8288 bus controller issues one ALE. The 8088 will not leave the HALT state when a local bus hold is entered while in HALT. In this case, the processor reissues the HALT indicator at the end of the local bus hold. An interrupt request or RESET will force the 8088 out of the HALT state. The LOCK status information is provided by the processor when consecutive bus cycles are required during the execution of an instruction. This allows the processor to perform read/modify/write operations on memory (via the ‘‘exchange register with memory’’ instruction), without another system bus master receiving intervening memory cycles. This is useful in multiprocessor system configurations to accomplish ‘‘test and set lock’’ operations. The LOCK signal is activated (LOW) in the clock cycle following decoding of the LOCK prefix instruction. It is deactivated at the end of the last bus cycle of the instruction following the LOCK prefix. While LOCK is active, a request on a RQ/GT pin will be recorded, and then honored at the end of the LOCK. 8088 231456 – 9 Figure 9. Interrupt Acknowledge Sequence External Synchronization via TEST As an alternative to interrupts, the 8088 provides a single software-testable input pin (TEST). This input is utilized by executing a WAIT instruction. The single WAIT instruction is repeatedly executed until the TEST input goes active (LOW). The execution of WAIT does not consume bus cycles once the queue is full. If a local bus request occurs during WAIT execution, the 8088 3-states all output drivers. If interrupts are enabled, the 8088 will recognize interrupts and process them. The WAIT instruction is then refetched, and reexecuted. Basic System Timing In minimum mode, the MN/MX pin is strapped to VCC and the processor emits bus control signals compatible with the 8085 bus structure. In maximum mode, the MN/MX pin is strapped to GND and the processor emits coded status information which the 8288 bus controller uses to generate MULTIBUS compatible bus control signals. System TimingÐMinimum System (See Figure 8) going) edge of this signal is used to latch the address information, which is valid on the address/ data bus (AD0 – AD7) at this time, into the 8282/8283 latch. Address lines A8 through A15 do not need to be latched because they remain valid throughout the bus cycle. From T1 to T4 the IO/M signal indicates a memory or I/O operation. At T2 the address is removed from the address/data bus and the bus goes to a high impedance state. The read control signal is also asserted at T2. The read (RD) signal causes the addressed device to enable its data bus drivers to the local bus. Some time later, valid data will be available on the bus and the addressed device will drive the READY line HIGH. When the processor returns the read signal to a HIGH level, the addressed device will again 3-state its bus drivers. If a transceiver is required to buffer the 8088 local bus, signals DT/R and DEN are provided by the 8088. A write cycle also begins with the assertion of ALE and the emission of the address. The IO/M signal is again asserted to indicate a memory or I/O write operation. In T2, immediately following the address emission, the processor emits the data to be written into the addressed location. This data remains valid until at least the middle of T4. During T2, T3, and Tw, the processor asserts the write control signal. The write (WR) signal becomes active at the beginning of T2, as opposed to the read, which is delayed somewhat into T2 to provide time for the bus to float. The read cycle begins in T1 with the assertion of the address latch enable (ALE) signal. The trailing (low 13 8088 The basic difference between the interrupt acknowledge cycle and a read cycle is that the interrupt acknowledge (INTA) signal is asserted in place of the read (RD) signal and the address bus is floated. (See Figure 9) In the second of two successive INTA cycles, a byte of information is read from the data bus, as supplied by the interrupt system logic (i.e. 8259A priority interrupt controller). This byte identifies the source (type) of the interrupt. It is multiplied by four and used as a pointer into the interrupt vector lookup table, as described earlier. Bus TimingÐMedium Complexity Systems (See Figure 10) For medium complexity systems, the MN/MX pin is connected to GND and the 8288 bus controller is added to the system, as well as a latch for latching the system address, and a transceiver to allow for bus loading greater than the 8088 is capable of handling. Signals ALE, DEN, and DT/R are generated by the 8288 instead of the processor in this configuration, although their timing remains relatively the same. The 8088 status outputs (S2, S1, and S0) provide type of cycle information and become 8288 inputs. This bus cycle information specifies read (code, data, or I/O), write (data or I/O), interrupt acknowledge, or software halt. The 8288 thus issues control signals specifying memory read or write, I/O read or write, or interrupt acknowledge. The 8288 provides two types of write strobes, normal and advanced, to be applied as required. The normal write strobes have data valid at the leading edge of write. The advanced write strobes have the same timing as read strobes, and hence, data is not valid at the leading edge of write. The transceiver receives the usual T and OE inputs from the 8288’s DT/R and DEN outputs. The pointer into the interrupt vector table, which is passed during the second INTA cycle, can derive from an 8259A located on either the local bus or the system bus. If the master 8289A priority interrupt controller is positioned on the local bus, a TTL gate is required to disable the transceiver when reading from the master 8259A during the interrupt acknowledge sequence and software ‘‘poll’’. The 8088 Compared to the 8086 The 8088 CPU is an 8-bit processor designed around the 8086 internal structure. Most internal functions of the 8088 are identical to the equivalent 8086 functions. The 8088 handles the external bus 14 the same way the 8086 does with the distinction of handling only 8 bits at a time. Sixteen-bit operands are fetched or written in two consecutive bus cycles. Both processors will appear identical to the software engineer, with the exception of execution time. The internal register structure is identical and all instructions have the same end result. The differences between the 8088 and 8086 are outlined below. The engineer who is unfamiliar with the 8086 is referred to the iAPX 86, 88 User’s Manual, Chapters 2 and 4, for function description and instruction set information. Internally, there are three differences between the 8088 and the 8086. All changes are related to the 8-bit bus interface. # The queue length is 4 bytes in the 8088, whereas the 8086 queue contains 6 bytes, or three words. The queue was shortened to prevent overuse of the bus by the BIU when prefetching instructions. This was required because of the additional time necessary to fetch instructions 8 bits at a time. # To further optimize the queue, the prefetching algorithm was changed. The 8088 BIU will fetch a new instruction to load into the queue each time there is a 1 byte hole (space available) in the queue. The 8086 waits until a 2-byte space is available. # The internal execution time of the instruction set is affected by the 8-bit interface. All 16-bit fetches and writes from/to memory take an additional four clock cycles. The CPU is also limited by the speed of instruction fetches. This latter problem only occurs when a series of simple operations occur. When the more sophisticated instructions of the 8088 are being used, the queue has time to fill and the execution proceeds as fast as the execution unit will allow. The 8088 and 8086 are completely software compatible by virtue of their identical execution units. Software that is system dependent may not be completely transferable, but software that is not system dependent will operate equally as well on an 8088 and an 8086. The hardware interface of the 8088 contains the major differences between the two CPUs. The pin assignments are nearly identical, however, with the following functional changes: # A8 – A15ÐThese pins are only address outputs on the 8088. These address lines are latched internally and remain valid throughout a bus cycle in a manner similar to the 8085 upper address lines. # BHE has no meaning on the 8088 and has been eliminated. 8088 # SSO provides the SO status information in the # IO/M has been inverted to be compatible with the minimum mode. This output occurs on pin 34 in minimum mode only. DT/R, IO/M, and SSO provide the complete bus status in minimum mode. # ALE is delayed by one clock cycle in the mini- MCS-85 bus structure. mum mode when entering HALT, to allow the status to be latched with ALE. 231456 – 10 Figure 10. Medium Complexity System Timing 15 8088 ABSOLUTE MAXIMUM RATINGS* NOTICE: This is a production data sheet. The specifications are subject to change without notice. Ambient Temperature Under Bias ÀÀÀÀ0§ C to a 70§ C Case Temperature (Plastic) ÀÀÀÀÀÀÀÀÀ0§ C to a 95§ C Case Temperature (CERDIP) ÀÀÀÀÀÀÀÀ0§ C to a 75§ C Storage Temperature ÀÀÀÀÀÀÀÀÀÀ b 65§ C to a 150§ C Voltage on Any Pin with Respect to Ground ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ b 1.0 to a 7V Power DissipationÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ2.5 Watt *WARNING: Stressing the device beyond the ‘‘Absolute Maximum Ratings’’ may cause permanent damage. These are stress ratings only. Operation beyond the ‘‘Operating Conditions’’ is not recommended and extended exposure beyond the ‘‘Operating Conditions’’ may affect device reliability. D.C. CHARACTERISTICS (TA e 0§ C to 70§ C, TCASE (Plastic) e 0§ C to 95§ C, TCASE (CERDIP) e 0§ C to 75§ C, TA e 0§ C to 55§ C and TCASE e 0§ C to 75§ C for P8088-2 only TA is guaranteed as long as TCASE is not exceeded) (VCC e 5V g 10% for 8088, VCC e 5V g 5% for 8088-2 and Extended Temperature EXPRESS) Min Max Units VIL Symbol Input Low Voltage Parameter b 0.5 a 0.8 V VIH Input High Voltage 2.0 VCC a 0.5 V (Notes 1, 2) VOL Output Low Voltage 0.45 V IOL e 2.0 mA VOH Output High Voltage V IOH e b 400 mA ICC 8088 Power Supply Current: 8088-2 P8088 340 350 250 mA TA e 25§ C ILI Input Leakage Current g 10 mA 0V s VIN s VCC (Note 3) ILO Output and I/O Leakage Current g 10 mA 0.45V s VOUT s VCC VCL Clock Input Low Voltage b 0.5 a 0.6 V VCH Clock Input High Voltage 3.9 VCC a 1.0 V CIN Capacitance If Input Buffer (All Input Except AD0 –AD7, RQ/GT) 15 pF fc e 1 MHz CIO Capacitance of I/O Buffer AD0 –AD7, RQ/GT) 15 pF fc e 1 MHz 2.4 NOTES: 1. VIL tested with MN/MX Pin e 0V VIH tested with MN/MX Pin e 5V MN/MX Pin is a strap Pin 2. Not applicable to RQ/GT0 and RQ/GT1 Pins (Pins 30 and 31) 3. HOLD and HLDA ILI Min e 30 mA, Max e 500 mA 16 Test Conditions (Note 1) 8088 A.C. CHARACTERISTICS (TA e 0§ C to 70§ C, TCASE (Plastic) e 0§ C to 95§ C, TCASE (CERDIP) e 0§ C to 75§ C, TA e 0§ C to 55§ C and TCASE e 0§ C to 80§ C for P8088-2 only TA is guaranteed as long as TCASE is not exceeded) (VCC e 5V g 10% for 8088, VCC e 5V g 5% for 8088-2 and Extended Temperature EXPRESS) MINIMUM COMPLEXITY SYSTEM TIMING REQUIREMENTS Symbol Parameter 8088 8088-2 Min Max Min Max 500 125 500 Units Test Conditions TCLCL CLK Cycle Period 200 TCLCH CLK Low Time 118 TCHCL CLK High Time 69 TCH1CH2 CLK Rise Time TCL2CL2 CLK Fall Time TDVCL Data in Setup Time TCLDX Data in Hold Time 10 10 ns TR1VCL RDY Setup Time into 8284 (Notes 1, 2) 35 35 ns TCLR1X RDY Hold Time into 8284 (Notes 1, 2) 0 0 ns TRYHCH READY Setup Time into 8088 118 68 ns TCHRYX READY Hold Time into 8088 30 20 ns TRYLCL READY Inactive to CLK (Note 3) b8 b8 ns THVCH HOLD Setup Time 35 20 ns TINVCH INTR, NMI, TEST Setup Time (Note 2) 30 15 ns TILIH Input Rise Time (Except CLK) 20 20 ns From 0.8V to 2.0V TIHIL Input Fall Time (Except CLK) 12 12 ns From 2.0V to 0.8V 68 44 10 ns 10 10 30 ns ns 10 20 ns From 1.0V to 3.5V ns From 3.5V to 1.0V ns 17 8088 A.C. CHARACTERISTICS (Continued) TIMING RESPONSES Symbol Parameter 8088 8088-2 Min Max 110 TCLAV Address Valid Delay 10 TCLAX Address Hold Time 10 TCLAX Min Max 10 60 10 80 TCLAX ns ns TCLAZ Address Float Delay TLHLL ALE Width TCLLH ALE Active Delay 80 50 ns TCHLL ALE Inactive Delay 85 55 ns TCLCH b 20 50 TCLCH b 10 ns ns TLLAX Address Hold Time to ALE Inactive TCLDV Data Valid Delay 10 TCHDX Data Hold Time 10 10 TWHDX Data Hold Time after WR TCLCH b 30 TCLCH b 30 TCVCTV Control Active Delay 1 10 110 10 70 ns TCHCTV Control Active Delay 2 10 110 10 60 ns TCVCTX Control Inactive Delay 10 110 10 70 ns TAZRL Address Float to READ Active 0 TCLRL RD Active Delay 10 165 10 100 ns TCLRH RD Inactive Delay 10 150 10 80 ns TRHAV RD Inactive to Next Address Active TCHCL b 10 TCHCL b 10 110 ns 60 ns ns TCLCL b 40 160 10 ns ns 0 TCLCL b 45 10 10 Test Conditions Units ns TCLHAV HLDA Valid Delay TRLRH RD Width 2TCLCL b 75 2TCLCL b 50 100 ns ns TWLWH WR Width 2TCLCL b 60 2TCLCL b 40 ns TAVAL Address Valid to ALE Low TCLCH b 60 TCLCH b 40 ns TOLOH Output Rise Time 20 20 ns From 0.8V to 2.0V TOHOL Output Fall Time 12 12 ns From 2.0V to 0.8V NOTES: 1. Signal at 8284A shown for reference only. See 8284A data sheet for the most recent specifications. 2. Set up requirement for asynchronous signal only to guarantee recognition at next CLK. 3. Applies only to T2 state (8 ns into T3 state). 18 8088 A.C. TESTING INPUT, OUTPUT WAVEFORM A.C. TESTING LOAD CIRCUIT 231456 – 11 A.C. Testing; Inputs are driven at 2.4V for a logic ‘‘1’’ and 0.45V for a logic ‘‘0’’. Timing measurements are made at 1.5V for both a logic ‘‘1’’ and logic ‘‘0’’. 231456 – 12 CL Includes Jig Capacitance WAVEFORMS BUS TIMINGÐMINIMUM MODE SYSTEM 231456 – 13 19 8088 WAVEFORMS (Continued) BUS TIMINGÐMINIMUM MODE SYSTEM (Continued) 231456 – 14 NOTES: 1. All signals switch between VOH and VOL unless otherwise specified. 2. RDY is sampled near the end of T2, T3, Tw to determine if Tw machines states are to be inserted. 3. Two INTA cycles run back-to-back. The 8088 local ADDR/DATA bus is floating during both INTA cycles. Control signals are shown for the second INTA cycle. 4. Signals at 8284 are shown for reference only. 5. All timing measurements are made at 1.5V unless otherwise noted. 20 8088 A.C. CHARACTERISTICS MAX MODE SYSTEM (USING 8288 BUS CONTROLLER) TIMING REQUIREMENTS Symbol Parameter 8088 8088-2 Min Max Min Max 500 125 500 Units Test Conditions TCLCL CLK Cycle Period 200 ns TCLCH CLK Low Time 118 68 ns TCHCL CLK High Time 69 44 ns TCH1CH2 CLK Rise Time 10 10 ns From 1.0V to 3.5V TCL2CL1 CLK Fall Time 10 10 ns From 3.5V to 1.0V TDVCL Data in Setup Time 30 20 ns TCLDX Data in Hold Time 10 10 ns TR1VCL RDY Setup Time into 8284 (Notes 1, 2) 35 35 ns TCLR1X RDY Hold Time into 8284 (Notes 1, 2) 0 0 ns TRYHCH READY Setup Time into 8088 118 68 ns TCHRYX READY Hold Time into 8088 30 20 ns TRYLCL READY Inactive to CLK (Note 4) b8 b8 ns TINVCH Setup Time for Recognition (INTR, NMI, TEST) (Note 2) 30 15 ns TGVCH RQ/GT Setup Time 30 15 ns TCHGX RQ Hold Time into 8088 40 30 ns TILIH Input Rise Time (Except CLK) 20 20 ns From 0.8V to 2.0V TIHIL Input Fall Time (Except CLK) 12 12 ns From 2.0V to 0.8V 21 8088 A.C. CHARACTERISTICS (Continued) TIMING RESPONSES Symbol TCLML TCLMH TRYHSH TCHSV TCLSH TCLAV TCLAX TCLAZ TSVLH TSVMCH TCLLH TCLMCH TCHLL TCLMCL TCLDV TCHDX TCVNV TCVNX TAZRL TCLRL TCLRH TRHAV TCHDTL TCHDTH TCLGL TCLGH TRLRH TOLOH TOHOL Parameter 8088 Min 10 Command Active Delay (Note 1) Command Inactive Delay 10 (Note 1) READY Active to Status Passive (Note 3) Status Active Delay 10 Status Inactive Delay 10 Address Valid Delay 10 Address Hold Time 10 Address Float Delay TCLAX Status Valid to ALE High (Note 1) Status Valid to MCE High (Note 1) CLK Low to ALE Valid (Note 1) CLK Low to MCE (Note 1) ALE Inactive Delay (Note 1) MCE Inactive Delay (Note 1) Data Valid Delay 10 Data Hold Time 10 Control Active Delay 5 (Note 1) Control Inactive Delay 10 (Note 1) Address Float to 0 Read Active RD Active Delay 10 RD Inactive Delay 10 RD Inactive to Next TCLCL b 45 Address Active Direction Control Active Delay (Note 1) Direction Control Inactive Delay (Note 1) GT Active Delay GT Inactive Delay RD Width 2TCLCL b 75 Output Rise Time Output Fall Time Max 35 35 8088-2 Units Min Max 10 35 ns 10 35 ns 65 ns 60 70 60 50 15 ns ns ns ns ns ns 15 15 ns 15 15 ns 15 15 15 110 15 15 15 60 110 110 130 110 80 15 10 10 10 10 TCLAX 45 10 10 5 45 ns ns ns ns ns ns 45 10 45 ns 0 165 150 10 10 TCLCL b 40 ns ns ns 50 50 ns 30 30 ns 85 85 50 50 ns ns ns ns ns 2TCLCL b 50 20 12 NOTES: 1. Signal at 8284 or 8288 shown for reference only. 2. Setup requirement for asynchronous signal only to guarantee recognition at next CLK. 3. Applies only to T3 and wait states. 4. Applies only to T2 state (8 ns into T3 state). 22 CL e 20 – 100 pF for All 8088 Outputs in Addition to Internal Loads ns 100 80 20 12 Test Conditions From 0.8V to 2.0V From 2.0V to 0.8V 8088 A.C. TESTING INPUT, OUTPUT WAVEFORM A.C. TESTING LOAD CIRCUIT 231456 – 11 A.C. Testing; Inputs are driven at 2.4V for a logic ‘‘1’’ and 0.45V for a logic ‘‘0’’. Timing measurements are made at 1.5V for both a logic ‘‘1’’ and logic ‘‘0’’. 231456 – 12 CL Includes Jig Capacitance WAVEFORMS (Continued) BUS TIMINGÐMAXIMUM MODE SYSTEM 231456 – 15 23 8088 WAVEFORMS (Continued) BUS TIMINGÐMAXIMUM MODE SYSTEM (USING 8288) NOTES: 231456 – 16 1. All signals switch between VOH and VOL unless otherwise specified. 2. RDY is sampled near the end of T2, T3, Tw to determine if Tw machines states are to be inserted. 3. Cascade address is valid between first and second INTA cycles. 4. Two INTA cycles run back-to-back. The 8088 local ADDR/DATA bus is floating during both INTA cycles. Control for pointer address is shown for second INTA cycle. 5. Signals at 8284 or 8288 are shown for reference only. 6. The issuance of the 8288 command and control signals (MRDC, MWTC, AMWC, IORC, IOWC, AIOWC, INTA and DEN) lags the active high 8288 CEN. 7. All timing measurements are made at 1.5V unless otherwise noted. 8. Status inactive in state just prior to T4. 24 8088 WAVEFORMS (Continued) ASYNCHRONOUS SIGNAL RECOGNITION BUS LOCK SIGNAL TIMING (MAXIMUM MODE ONLY) NOTE: 231456 – 17 1. Setup requirements for asynchronous signals only to guarantee recognition at next CLK. 231456 – 18 REQUEST/GRANT SEQUENCE TIMING (MAXIMUM MODE ONLY) NOTE: 1. The coprocessor may not drive the busses outside the region shown without risking contention. 231456 – 19 HOLD/HOLD ACKNOWLEDGE TIMING (MINIMUM MODE ONLY) 231456 – 20 25 8088 8086/8088 Instruction Set Summary Mnemonic and Description Instruction Code DATA TRANSFER MOV e Move: 76543210 Register/Memory to/from Register 100010dw Immediate to Register/Memory 76543210 76543210 1100011w 1 0 1 1 w reg mod 0 0 0 r/m data data if w e 1 data data if w e 1 Memory to Accumulator Accumulator to Memory 1010000w addr-low addr-high 1010001w addr-low addr-high Register/Memory to Segment Register 10001110 mod 0 reg r/m Segment Register to Register/Memory 10001100 mod 0 reg r/m 11111111 mod 1 1 0 r/m Immediate to Register 76543210 mod reg r/m PUSH e Push: Register/Memory Register Segment Register 0 1 0 1 0 reg 0 0 0 reg 1 1 0 POP e Pop: Register/Memory Register Segment Register 10001111 mod 0 0 0 r/m 0 1 0 1 1 reg 0 0 0 reg 1 1 1 XCHG e Exchange: Register/Memory with Register Register with Accumulator 1000011w mod reg r/m 1 0 0 1 0 reg IN e Input from: Fixed Port 1110010w Variable Port 1110110w port OUT e Output to: Fixed Port 1110011w Variable Port 1110111w XLAT e Translate Byte to AL 11010111 port LEA e Load EA to Register 10001101 mod reg r/m LDS e Load Pointer to DS 11000101 mod reg r/m LES e Load Pointer to ES 11000100 mod reg r/m LAHF e Load AH with Flags 10011111 SAHF e Store AH into Flags 10011110 PUSHF e Push Flags 10011100 POPF e Pop Flags 10011101 26 8088 8086/8088 Instruction Set Summary (Continued) Mnemonic and Description ARITHMETIC Instruction Code 76543210 76543210 76543210 76543210 data if s:w e 01 ADD e Add: Reg./Memory with Register to Either 000000dw mod reg r/m Immediate to Register/Memory 100000sw mod 0 0 0 r/m data Immediate to Accumulator 0000010w data data if w e 1 ADC e Add with Carry: Reg./Memory with Register to Either 000100dw mod reg r/m Immediate to Register/Memory 100000sw mod 0 1 0 r/m data 0001010w data data if w e 1 1111111w mod 0 0 0 r/m Immediate to Accumulator data if s:w e 01 INC e Increment: Register/Memory Register 0 1 0 0 0 reg AAA e ASCII Adjust for Add 00110111 BAA e Decimal Adjust for Add 00100111 SUB e Subtract: Reg./Memory and Register to Either 001010dw mod reg r/m Immediate from Register/Memory 100000sw mod 1 0 1 r/m data Immediate from Accumulator 0010110w data data if w e 1 data if s:w e 01 SSB e Subtract with Borrow Reg./Memory and Register to Either 000110dw mod reg r/m Immediate from Register/Memory 100000sw mod 0 1 1 r/m data 000111w data data if w e 1 1111111w mod 0 0 1 r/m Immediate from Accumulator data if s:w e 01 DEC e Decrement: Register/memory Register NEG e Change sign 0 1 0 0 1 reg 1111011w mod 0 1 1 r/m CMP e Compare: Register/Memory and Register 001110dw mod reg r/m Immediate with Register/Memory 100000sw mod 1 1 1 r/m data Immediate with Accumulator 0011110w data data if w e 1 AAS e ASCII Adjust for Subtract 00111111 DAS e Decimal Adjust for Subtract 00101111 MUL e Multiply (Unsigned) 1111011w mod 1 0 0 r/m IMUL e Integer Multiply (Signed) 1111011w mod 1 0 1 r/m AAM e ASCII Adjust for Multiply 11010100 00001010 DIV e Divide (Unsigned) 1111011w mod 1 1 0 r/m IDIV e Integer Divide (Signed) 1111011w mod 1 1 1 r/m AAD e ASCII Adjust for Divide 11010101 00001010 CBW e Convert Byte to Word 10011000 CWD e Convert Word to Double Word 10011001 data if s:w e 01 27 8088 8086/8088 Instruction Set Summary (Continued) Mnemonic and Description Instruction Code LOGIC 76543210 76543210 NOT e Invert 1111011w mod 0 1 0 r/m SHL/SAL e Shift Logical/Arithmetic Left 110100vw mod 1 0 0 r/m SHR e Shift Logical Right 110100vw mod 1 0 1 r/m SAR e Shift Arithmetic Right 110100vw mod 1 1 1 r/m ROL e Rotate Left 110100vw mod 0 0 0 r/m ROR e Rotate Right 110100vw mod 0 0 1 r/m RCL e Rotate Through Carry Flag Left 110100vw mod 0 1 0 r/m RCR e Rotate Through Carry Right 110100vw mod 0 1 1 r/m 76543210 76543210 data if w e 1 AND e And: Reg./Memory and Register to Either 001000dw mod reg r/m Immediate to Register/Memory 1000000w mod 1 0 0 r/m data Immediate to Accumulator 0010010w data data if w e 1 Register/Memory and Register 1000010w mod reg r/m Immediate Data and Register/Memory 1111011w mod 0 0 0 r/m data Immediate Data and Accumulator 1010100w data data if w e 1 TEST e And Function to Flags. No Result: data if w e 1 OR e Or: Reg./Memory and Register to Either 000010dw mod reg r/m Immediate to Register/Memory 1000000w mod 0 0 1 r/m data data data if w e 1 Immediate to Accumulator 0000110w data if w e 1 XOR e Exclusive or: Reg./Memory and Register to Either 001100dw mod reg r/m Immediate to Register/Memory 1000000w mod 1 1 0 r/m data Immediate to Accumulator 0011010w data data if w e 1 disp-high STRING MANIPULATION REP e Repeat 1111001z MOVS e Move Byte/Word 1010010w CMPS e Compare Byte/Word 1010011w SCAS e Scan Byte/Word 1010111w LODS e Load Byte/Wd to AL/AX 1010110w STOS e Stor Byte/Wd from AL/A 1010101w CONTROL TRANSFER CALL e Call: Direct Within Segment 11101000 disp-low Indirect Within Segment 11111111 mod 0 1 0 r/m Direct Intersegment 10011010 offset-low offset-high seg-low seg-high Indirect Intersegment 28 11111111 mod 0 1 1 r/m data if w e 1 8088 8086/8088 Instruction Set Summary (Continued) Mnemonic and Description Instruction Code JMP e Unconditional Jump: 76543210 76543210 76543210 Direct Within Segment 11101001 disp-low disp-high Direct Within Segment-Short 11101011 disp Indirect Within Segment 11111111 mod 1 0 0 r/m Direct Intersegment 11101010 offset-low offset-high seg-low seg-high Indirect Intersegment 11111111 mod 1 0 1 r/m RET e Return from CALL: Within Segment 11000011 Within Seg Adding Immed to SP 11000010 Intersegment 11001011 data-low data-high data-high Intersegment Adding Immediate to SP 11001010 data-low JE/JZ e Jump on Equal/Zero 01110100 disp JL/JNGE e Jump on Less/Not Greater or Equal JLE/JNG e Jump on Less or Equal/ Not Greater 01111100 disp 01111110 disp JB/JNAE e Jump on Below/Not Above 01110010 disp 01110110 disp 01111010 disp JO e Jump on Overflow 01110000 disp JS e Jump on Sign 01111000 disp JNE/JNZ e Jump on Not Equal/Not Zero 01110101 disp JNL/JGE e Jump on Not Less/Greater or Equal JNLE/JG e Jump on Not Less or Equal/ Greater JNB/JAE e Jump on Not Below/Above or Equal JNBE/JA e Jump on Not Below or Equal/Above JNP/JPO e Jump on Not Par/Par Odd 01111101 disp 01111111 disp 01110011 disp 01110111 disp 01111011 disp JNO e Jump on Not Overflow 01110001 disp JNS e Jump on Not Sign 01111001 disp LOOP e Loop CX Times 11100010 disp or Equal JBE/JNA e Jump on Below or Equal/ Not Above JP/JPE e Jump on Parity/Parity Even LOOPZ/LOOPE e Loop While Zero/Equal 11100001 disp LOOPNZ/LOOPNE e Loop While Not Zero/Equal JCXZ e Jump on CX Zero 11100000 disp 11100011 disp Type Specified 11001101 type Type 3 11001100 INTO e Interrupt on Overflow 11001110 IRET e Interrupt Return 11001111 INT e Interrupt 29 8088 8086/8088 Instruction Set Summary (Continued) Mnemonic and Description Instruction Code 76543210 76543210 PROCESSOR CONTROL CLC e Clear Carry 11111000 CMC e Complement Carry 11110101 STC e Set Carry 11111001 CLD e Clear Direction 11111100 STD e Set Direction 11111101 CLI e Clear Interrupt 11111010 STI e Set Interrupt 11111011 HLT e Halt 11110100 WAIT e Wait 10011011 ESC e Escape (to External Device) 11011xxx LOCK e Bus Lock Prefix 11110000 NOTES: AL e 8-bit accumulator AX e 16-bit accumulator CX e Count register DS e Data segment ES e Extra segment Above/below refers to unsigned value Greater e more positive: Less e less positive (more negative) signed values if d e 1 then ‘‘to’’ reg; if d e 0 then ‘‘from’’ reg if w e 1 then word instruction; if w e 0 then byte instruction if mod e 11 then r/m is treated as a REG field if mod e 00 then DISP e 0*, disp-low and disp-high are absent if mod e 01 then DISP e disp-low sign-extended to 16 bits, disp-high is absent if mod e 10 then DISP e disp-high; disp-low if r/m e 000 then EA e (BX) a (SI) a DISP if r/m e 001 then EA e (BX) a (DI) a DISP if r/m e 010 then EA e (BP) a (SI) a DISP if r/m e 011 then EA e (BP) a (DI) a DISP if r/m e 100 then EA e (SI) a DISP if r/m e 101 then EA e (DI) a DISP if r/m e 110 then EA e (BP) a DISP* if r/m e 111 then EA e (BX) a DISP DISP follows 2nd byte of instruction (before data if required) *except if mod e 00 and r/m e then EA e disp-high: disp-low. if s:w e 01 then 16 bits of immediate data form the operand if s:w e 11 then an immediate data byte is sign extended to form the 16-bit operand if v e 0 then ‘‘count’’ e 1; if v e 1 then ‘‘count’’ in (CL) register x e don’t care z is used for string primitives for comparison with ZF FLAG SEGMENT OVERRIDE PREFIX 0 0 1 reg 1 1 0 30 mod x x x r/m REG is assigned according to the following table: 16-Bit (w e 1) 000 AX 001 CX 010 DX 011 BX 100 SP 101 BP 110 SI 111 DI 8-Bit (w e 0) 000 AL 001 CL 010 DL 011 BL 100 AH 101 CH 110 DH 111 BH Segment 00 ES 01 CS 10 SS 11 DS Instructions which reference the flag register file as a 16-bit object use the symbol FLAGS to represent the file: FLAGS e X:X:X:X:(OF):(DF):(IF):(TF):(SF):(ZF):X:(AF):X:(PF):X:(CF) Mnemonics © Intel, 1978 DATA SHEET REVISION REVIEW The following list represents key differences between this and the -005 data sheet. Please review this summary carefully. 1. The Intel 8088 implementation technology (HMOS) has been changed to (HMOS-II).