ATMEL AT89C55-33JC

AT89C55
Features
• Compatible with MCS-51™ Products
• 20K Bytes of In-System Reprogrammable Flash Memory
•
•
•
•
•
•
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– Endurance: 1,000 Write/Erase Cycles
Fully Static Operation: 0 Hz to 33 MHz
Three-Level Program Memory Lock
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Eight Interrupt Sources
Low Power Idle and Power Down Modes
Description
The AT89C55 is a low-power, high-performance CMOS 8-bit microcomputer with 20K
bytes of Flash programmable and erasable read only memory. The device is manufactured using Atmel’s high density nonvolatile memory technology and is compatible
with the industry standard 80C51 instruction set and pinout. The on-chip Flash allows
the program memory to be reprogrammed in-system or by a conventional nonvolatile
memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic
chip, the Atmel AT89C55 is a powerful microcomputer which provides a highly flexible
and cost effective solution to many embedded control applications.
(continued)
Pin Configurations
PDIP
PQFP/TQFP
PLCC
8-Bit
Microcontroller
with 20K Bytes
Flash
AT89C55
0580D-A–12/97
4-169
Block Diagram
P0.0 - P0.7
P2.0 - P2.7
PORT 0 DRIVERS
PORT 2 DRIVERS
VCC
GND
RAM ADDR.
REGISTER
B
REGISTER
PORT 0
LATCH
RAM
PORT 2
LATCH
FLASH
STACK
POINTER
ACC
PROGRAM
ADDRESS
REGISTER
BUFFER
TMP2
TMP1
PC
INCREMENTER
ALU
INTERRUPT, SERIAL PORT,
AND TIMER BLOCKS
PROGRAM
COUNTER
PSW
PSEN
ALE/PROG
EA / VPP
TIMING
AND
CONTROL
INSTRUCTION
REGISTER
DPTR
RST
PORT 1
LATCH
PORT 3
LATCH
PORT 1 DRIVERS
PORT 3 DRIVERS
OSC
P1.0 - P1.7
4-170
AT89C55
P3.0 - P3.7
AT89C55
The AT89C55 provides the following standard features:
20K bytes of Flash, 256-bytes of RAM, 32 I/O lines, three
16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and
clock circuitry. In addition, the AT89C55 is designed with
static logic for operation down to zero frequency and supports two software selectable power saving modes. The
Idle Mode stops the CPU while allowing the RAM,
timer/counters, serial port, and interrupt system to continue
functioning. The Power Down Mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next hardware reset. The low-voltage option
saves power and operates with a 2.7-volt power supply.
Pin Description
VCC
Supply voltage.
GND
Ground.
Port 0
Port 0 is an 8-bit open drain bidirectional I/O port. As an
output port, each pin can sink eight TTL inputs. When 1s
are written to port 0 pins, the pins can be used as highimpedance inputs.
Port 0 can also be configured to be the multiplexed loworder address/data bus during accesses to external program and data memory. In this mode, P0 has internal pullups.
Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pullups are required during program verification.
Port 1
Port 1 is an 8-bit bidirectional I/O port with internal pullups.
The Port 1 output buffers can sink/source four TTL inputs.
When 1s are written to Port 1 pins, they are pulled high by
the internal pullups and can be used as inputs. As inputs,
Port 1 pins that are externally being pulled low will source
current (IIL) because of the internal pullups.
In addition, P1.0 and P1.1 can be configured to be the
timer/counter 2 external count input (P1.0/T2) and the
timer/counter 2 trigger input (P1.1/T2EX), respectively, as
shown in the following table.
Port Pin
Alternate Functions
P1.0
T2 (external count input to Timer/Counter 2),
clock-out
P1.1
T2EX (Timer/Counter 2 capture/reload
trigger and direction control)
Port 2
Port 2 is an 8-bit bidirectional I/O port with internal pullups.
The Port 2 output buffers can sink/source four TTL inputs.
When 1s are written to Port 2 pins, they are pulled high by
the internal pullups and can be used as inputs. As inputs,
Port 2 pins that are externally being pulled low will source
current (IIL) because of the internal pullups.
Port 2 emits the high-order address byte during fetches
from external program memory and during accesses to
external data memory that use 16-bit addresses (MOVX @
DPTR). In this application, Port 2 uses strong internal pullups when emitting 1s. During accesses to external data
memory that use 8-bit addresses (MOVX @ RI), Port 2
emits the contents of the P2 Special Function Register.
Port 2 also receives the high-order address bits and some
control signals during Flash programming and verification.
Port 3
Port 3 is an 8-bit bidirectional I/O port with internal pullups.
The Port 3 output buffers can sink/source four TTL inputs.
When 1s are written to Port 3 pins, they are pulled high by
the internal pullups and can be used as inputs. As inputs,
Port 3 pins that are externally being pulled low will source
current (IIL) because of the pullups.
Port 3 also serves the functions of various special features
of the AT89C55, as shown in the following table.
Port Pin
Alternate Functions
P3.0
RXD (serial input port)
P3.1
TXD (serial output port)
P3.2
INT0 (external interrupt 0)
P3.3
INT1 (external interrupt 1)
P3.4
T0 (timer 0 external input)
P3.5
T1 (timer 1 external input)
P3.6
WR (external data memory write strobe)
P3.7
RD (external data memory read strobe)
Port 3 also receives the highest-order address bit and
some control signals for Flash programming and verification.
RST
Reset input. A high on this pin for two machine cycles while
the oscillator is running resets the device.
Port 1 also receives the low-order address bytes during
Flash programming and verification.
4-171
ALE/PROG
Address Latch Enable is an output pulse for latching the
low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming.
In normal operation, ALE is emitted at a constant rate of
1/6 the oscillator frequency and may be used for external
timing or clocking purposes. Note, however, that one ALE
pulse is skipped during each access to external data memory.
If desired, ALE operation can be disabled by setting bit 0 of
SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is
weakly pulled high. Setting the ALE-disable bit has no
effect if the microcontroller is in external execution mode.
PSEN
Program Store Enable is the read strobe to external program memory.
When the AT89C55 is executing code from external program memory, PSEN is activated twice each machine
cycle, except that two PSEN activations are skipped during
each access to external data memory.
EA/VPP
External Access Enable. EA must be strapped to GND in
order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH.
Note, however, that if lock bit 1 is programmed, EA will be
internally latched on reset.
EA should be strapped to VCC for internal program executions.
This pin also receives the 12-volt programming enable voltage (VPP) during 12-volt Flash programming.
XTAL1
Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
Special Function Registers
A map of the on-chip memory area called the Special
Function Register (SFR) space is shown in Table 1.
Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip.
Read accesses to these addresses will in general return
random data, and write accesses will have an indeterminate effect.
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AT89C55
User software should not write 1s to these unlisted locations, since they may be used in future products to invoke
new features. In that case, the reset or inactive values of
the new bits will always be 0.
Timer 2 Registers Control and status bits are contained in
registers T2CON (shown in Table 2) and T2MOD (shown
in Table 4) for Timer 2. The register pair (RCAP2H,
RCAP2L) are the Capture/Reload registers for Timer 2 in
16 bit capture mode or 16-bit auto-reload mode.
Interrupt Registers The individual interrupt enable bits are
in the IE register. Two priorities can be set for each of the
six interrupt sources in the IP register.
Data Memory
The AT89C55 implements 256-bytes of on-chip RAM. The
upper 128-bytes occupy a parallel address space to the
Special Function Registers. That means the upper 128bytes have the same addresses as the SFR space but are
physically separate from SFR space.
When an instruction accesses an internal location above
address 7FH, the address mode used in the instruction
specifies whether the CPU accesses the upper 128-bytes
of RAM or the SFR space. Instructions that use direct
addressing access SFR space.
For example, the following direct addressing instruction
accesses the SFR at location 0A0H (which is P2).
MOV 0A0H, #data
Instructions that use indirect addressing access the upper
128-bytes of RAM. For example, the following indirect
addressing instruction, where R0 contains 0A0H, accesses
the data byte at address 0A0H, rather than P2 (whose
address is 0A0H).
MOV @R0, #data
Note that stack operations are examples of indirect
addressing, so the upper 128-bytes of data RAM are available as stack space.
AT89C55
Table 1. AT89C55 SFR Map and Reset Values
0F8H
0F0H
0FFH
B
00000000
0F7H
0E8H
0E0H
0EFH
ACC
00000000
0E7H
0D8H
0DFH
0D0H
PSW
00000000
0C8H
T2CON
00000000
0D7H
T2MOD
XXXXXX00
RCAP2L
00000000
RCAP2H
00000000
TL2
00000000
TH2
00000000
0CFH
0C0H
0C7H
0B8H
IP
XX000000
0BFH
0B0H
P3
11111111
0B7H
0A8H
IE
0X000000
0AFH
0A0H
P2
11111111
0A7H
98H
SCON
00000000
90H
P1
11111111
88H
TCON
00000000
TMOD
00000000
TL0
00000000
TL1
00000000
80H
P0
11111111
SP
00000111
DPL
00000000
DPH
00000000
SBUF
XXXXXXXX
9FH
97H
TH0
00000000
TH1
00000000
8FH
PCON
0XXX0000
87H
4-173
Table 2. T2CON—Timer/Counter 2 Control Register
T2CON Address = 0C8H
Reset Value = 0000 0000B
Bit Addressable
Bit
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2
CP/RL2
7
6
5
4
3
2
1
0
Symbol
Function
TF2
Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set when either RCLK
= 1 or TCLK = 1.
EXF2
Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and EXEN2 = 1.
When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2 interrupt routine. EXF2 must
be cleared by software. EXF2 does not cause an interrupt in up/down counter mode (DCEN = 1).
RCLK
Receive clock enable. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock in serial port
Modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for the receive clock.
TCLK
Transmit clock enable. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock in serial
port Modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for the transmit clock.
EXEN2
Timer 2 external enable. When set, allows a capture or reload to occur as a result of a negative transition on T2EX if
Timer 2 is not being used to clock the serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX.
TR2
Start/Stop control for Timer 2. TR2 = 1 starts the timer.
C/T2
Timer or counter select for Timer 2. C/T2 = 0 for timer function. C/T2 = 1 for external event counter (falling edge
triggered).
CP/RL2
Capture/Reload select. CP/RL2 = 1 causes captures to occur on negative transitions at T2EX if EXEN2 = 1. CP/RL2 =
0 causes automatic reloads to occur when Timer 2 overflows or negative transitions occur at T2EX when EXEN2 = 1.
When either RCLK or TCLK = 1, this bit is ignored and the timer is forced to auto-reload on Timer 2 overflow.
4-174
AT89C55
AT89C55
Timer 0 and 1
Timer 0 and Timer 1 in the AT89C55 operate the same way
as Timer) and Timer 1 in the AT89C51 and AT89C52. For
further information, see the Microcontroller Data Book, section titled, “Timer/Counters.”
Timer 2
Timer 2 is a 16 bit Timer/Counter that can operate as either
a timer or an event counter. The type of operation is
selected by bit C/T2 in the SFR T2CON (shown in Table 2).
Timer 2 has three operating modes: capture, auto-reload
(up or down counting), and baud rate generator. The
modes are selected by bits in T2CON, as shown in Table 3.
Timer 2 consists of two 8-bit registers, TH2 and TL2. In the
Timer function, the TL2 register is incremented every
machine cycle. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/12 of the oscillator frequency.
In the Counter function, the register is incremented in
response to a 1-to-0 transition at its corresponding external
input pin, T2. In this function, the external input is sampled
during S5P2 of every machine cycle. When the samples
Table 3. Timer 2 Operating Modes
RCLK + TCLK
CP/RL2
TR2
MODE
0
0
1
16 bit Auto-Reload
0
1
1
16 bit Capture
1
X
1
Baud Rate Generator
X
X
0
(Off)
show a high in one cycle and a low in the next cycle, the
count is incremented. The new count value appears in the
register during S3P1 of the cycle following the one in which
the transition was detected. Since two machine cycles (24
oscillator periods) are required to recognize a 1-to-0 transition, the maximum count rate is 1/24 of the oscillator frequency. To ensure that a given level is sampled at least
once before it changes, the level should be held for at least
one full machine cycle.
Capture Mode
In the capture mode, two options are selected by bit
EXEN2 in T2CON. If EXEN2 = 0, Timer 2 is a 16 bit timer
or counter which upon overflow sets bit TF2 in T2CON.
This bit can then be used to generate an interrupt. If
EXEN2 = 1, Timer 2 performs the same operation, but a 1to-0 transition at external input T2EX also causes the current value in TH2 and TL2 to be captured into RCAP2H and
RCAP2L, respectively. In addition, the transition at T2EX
causes bit EXF2 in T2CON to be set. The EXF2 bit, like
TF2, can generate an interrupt. The capture mode is illustrated in Figure 1.
Auto-Reload (Up or Down Counter)
Timer 2 can be programmed to count up or down when
configured in its 16-bit auto-reload mode. This feature is
invoked by the DCEN (Down Counter Enable) bit located in
the SFR T2MOD (see Table 4). Upon reset, the DCEN bit
is set to 0 so that timer 2 will default to count up. When
DCEN is set, Timer 2 can count up or down, depending on
the value of the T2EX pin.
Figure 2 shows Timer 2 automatically counting up when
DCEN = 0. In this mode, two options are selected by bit
EXEN2 in T2CON. If EXEN2 = 0, Timer 2 counts up to
0FFFFH and then sets the TF2 bit upon overflow. The overflow also causes the timer registers to be reloaded with the
16 bit value in RCAP2H and RCAP2L. The values in
RCAP2H and RCAP2L are preset by software. If EXEN2 =
Figure 1. Timer 2 in Capture Mode
4-175
1, a 16 bit reload can be triggered either by an overflow or
by a 1-to-0 transition at external input T2EX. This transition
also sets the EXF2 bit. Both the TF2 and EXF2 bits can
generate an interrupt if enabled.
Setting the DCEN bit enables Timer 2 to count up or down,
as shown in Figure 3. In this mode, the T2EX pin controls
the direction of the count. A logic 1 at T2EX makes Timer 2
count up. The timer will overflow at 0FFFFH and set the
TF2 bit. This overflow also causes the 16 bit value in
RCAP2H and RCAP2L to be reloaded into the timer registers, TH2 and TL2, respectively.
A logic 0 at T2EX makes Timer 2 count down. The timer
underflows when TH2 and TL2 equal the values stored in
RCAP2H and RCAP2L. The underflow sets the TF2 bit and
causes 0FFFFH to be reloaded into the timer registers.
The EXF2 bit toggles whenever Timer 2 overflows or
underflows and can be used as a 17th bit of resolution. In
this operating mode, EXF2 does not flag an interrupt.
Figure 2. Timer 2 Auto Reload Mode (DCEN = 0)
Table 4. T2MOD—Timer 2 Mode Control Register
T2MOD Address = 0C9H
Reset Value = XXXX XX00B
Not Bit Addressable
Bit
—
—
—
—
—
—
T20E
DCEN
7
6
5
4
3
2
1
0
Symbol
Function
—
Not implemented, reserved for future use.
T20E
Timer 2 Output Enable bit.
DCEN
When set, this bit allows Timer 2 to be configured as an up/down counter.
4-176
AT89C55
AT89C55
Figure 3. Timer 2 Auto Reload Mode (DCEN = 1)
(DOWN COUNTING RELOAD VALUE)
0FFH
OSC
÷12
TOGGLE
0FFH
EXF2
OVERFLOW
C/T2 = 0
TH2
TL2
TF2
CONTROL
TR2
C/T2 = 1
TIMER 2
INTERRUPT
T2 PIN
RCAP2H RCAP2L
(UP COUNTING RELOAD VALUE)
COUNT
DIRECTION
1=UP
0=DOWN
T2EX PIN
Figure 4. Timer 2 in Baud Rate Generator Mode
4-177
Baud Rate Generator
Timer 2 is selected as the baud rate generator by setting
TCLK and/or RCLK in T2CON (Table 2). Note that the baud
rates for transmit and receive can be different if Timer 2 is
used for the receiver or transmitter and Timer 1 is used for
the other function. Setting RCLK and/or TCLK puts Timer 2
into its baud rate generator mode, as shown in Figure 4.
The baud rate generator mode is similar to the auto-reload
mode, in that a rollover in TH2 causes the Timer 2 registers
to be reloaded with the 16 bit value in registers RCAP2H
and RCAP2L, which are preset by software.
The baud rates in Modes 1 and 3 are determined by Timer
2’s overflow rate according to the following equation.
Timer 2 Overflow Rate
Modes 1 and 3 Baud Rates = -----------------------------------------------------------16
The Timer can be configured for either timer or counter
operation. In most applications, it is configured for timer
operation (CP/T2 = 0). The timer operation is different for
Timer 2 when it is used as a baud rate generator. Normally,
as a timer, it increments every machine cycle (at 1/12 the
oscillator frequency). As a baud rate generator, however, it
increments every state time (at 1/2 the oscillator frequency). The baud rate formula is given below.
Figure 5. Timer 2 in Clock-Out Mode
4-178
AT89C55
Modes 1 and 3
Oscillator Frequency
--------------------------------------- = -------------------------------------------------------------------------------------------------Baud Rate
32 × [ 655536 – ( RCAP2H,RCAP2L ) ]
where (RCAP2H, RCAP2L) is the content of RCAP2H and
RCAP2L taken as a 16 bit unsigned integer.
Timer 2 as a baud rate generator is shown in Figure 4. This
figure is valid only if RCLK or TCLK = 1 in T2CON. Note
that a rollover in TH2 does not set TF2 and will not generate an interrupt. Note too, that if EXEN2 is set, a 1-to-0
transition in T2EX will set EXF2 but will not cause a reload
from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer
2 is in use as a baud rate generator, T2EX can be used as
an extra external interrupt.
Note that when Timer 2 is running (TR2 = 1) as a timer in
the baud rate generator mode, TH2 or TL2 should not be
read from or written to. Under these conditions, the Timer is
incremented every state time, and the results of a read or
write may not be accurate. The RCAP2 registers may be
read but should not be written to, because a write might
overlap a reload and cause write and/or reload errors. The
timer should be turned off (clear TR2) before accessing the
Timer 2 or RCAP2 registers.
AT89C55
Programmable Clock Out
A 50% duty cycle clock can be programmed to come out on
P1.0, as shown in Figure 5. This pin, besides being a regular I/O pin, has two alternate functions. It can be programmed to input the external clock for Timer/Counter 2 or
to output a 50% duty cycle clock ranging from 61 Hz to 4
MHz at a 16 MHz operating frequency.
To configure the Timer/Counter 2 as a clock generator, bit
C/T2 (T2CON.1) must be cleared and bit T2OE (T2MOD.1)
must be set. Bit TR2 (T2CON.2) starts and stops the timer.
The clock-out frequency depends on the oscillator frequency and the reload value of Timer 2 capture registers
(RCAP2H, TCAP2L), as shown in the following equation:
Oscillator Frequency
Clock-Out Frequency = ---------------------------------------------------------------------------------------------4 × [ 655536 – ( RCAP2H,RCAP2L) ]
In the clock-out mode, Timer 2 roll-overs will not generate
an interrupt. This behavior is similar to when Timer 2 is
used as a baud-rate generator. It is possible to use Timer 2
as a baud-rate generator and a clock generator simultaneously. Note, however, that the baud-rate and clock-out
frequencies cannot be determined independently from one
another since they both use RCAP2H and RCAP2L.
UART
The UART in the AT89C55 operates the same way as the
UART in the AT89C51 and AT89C52. For further information, see the Microcontroller Data Book, section titled,
“Serial Interface.”
Table 5. Interrupt Enable (IE) Register
(MSB)
EA
(LSB)
—
ET2
ES
ET1
EX1
ET0
EX0
Enable Bit = 1 enables the interrupt.
Enable Bit = 0 disables the interrupt.
Symbol
Position
Function
EA
IE.7
Disables all interrupts. If EA = 0, no
interrupt is acknowledged. If EA =
1, each interrupt source is
individually enabled or disabled by
setting or clearing its enable bit.
—
IE.6
Reserved.
ET2
IE.5
Timer 2 interrupt enable bit.
ES
IE.4
Serial Port interrupt enable bit.
ET1
IE.3
Timer 1 interrupt enable bit.
EX1
IE.2
External interrupt 1 enable bit.
ET0
IE.1
Timer 0 interrupt enable bit.
EX0
IE.0
External interrupt 0 enable bit.
User software should never write 1s to unimplemented bits,
because they may be used in future AT89 products.
Figure 6. Interrupt Sources
Interrupts
The AT89C55 has a total of six interrupt vectors: two external interrupts (INT0 and INT1), three timer interrupts (Timers 0, 1, and 2), and the serial port interrupt. These interrupts are all shown in Figure 6.
Each of these interrupt sources can be individually enabled
or disabled by setting or clearing a bit in Special Function
Register IE. IE also contains a global disable bit, EA, which
disables all interrupts at once.
Note that Table 5 shows that bit position IE.6 is unimplemented. In the AT89C51 and AT89LV51, bit position IE.5 is
also unimplemented. User software should not write 1s to
these bit positions, since they may be used in future AT89
products.
Timer 2 interrupt is generated by the logical OR of bits TF2
and EXF2 in register T2CON. Neither of these flags is
cleared by hardware when the service routine is vectored
to. In fact, the service routine may have to determine
whether it was TF2 or EXF2 that generated the interrupt,
and that bit will have to be cleared in software.
The Timer 0 and Timer 1 flags, TF0 and TF1, are set at
S5P2 of the cycle in which the timers overflow. The values
are then polled by the circuitry in the next cycle. However,
4-179
the Timer 2 flag, TF2, is set at S2P2 and is polled in the
same cycle in which the timer overflows. For further information, see the Microcontroller Data Book, section titled
“Interrupts.”
Figure 7. Oscillator Connections
Oscillator Characteristics
XTAL1 and XTAL2 are the input and output, respectively,
of an inverting amplifier that can be configured for use as
an on-chip oscillator, as shown in Figure 7. Either a quartz
crystal or ceramic resonator may be used. To drive the
device from an external clock source, XTAL2 should be left
unconnected while XTAL1 is driven, as shown in Figure 8.
There are no requirements on the duty cycle of the external
clock signal, since the input to the internal clocking circuitry
is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be
observed.
Note:
C1,C2
= ± 30 pF for Crystals
= ± 40 pF for Ceramic Resonators
Figure 8. External Clock Drive Configuration
Idle Mode
In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The mode is invoked by
software. The content of the on-chip RAM and all the special functions registers remain unchanged during this
mode. The idle mode can be terminated by any enabled
interrupt or by a hardware reset.
Note that when idle mode is terminated by a hardware
reset, the device normally resumes program execution
from where it left off, up to two machine cycles before the
internal reset algorithm takes control. On-chip hardware
inhibits access to internal RAM in this event, but access to
the port pins is not inhibited. To eliminate the possibility of
an unexpected write to a port pin when idle mode is terminated by a reset, the instruction following the one that
invokes idle mode should not write to a port pin or to external memory.
Status of External Pins During Idle and Power Down Modes
Mode
Program Memory
ALE
PSEN
PORT0
PORT1
PORT2
PORT3
Idle
Internal
1
1
Data
Data
Data
Data
Idle
External
1
1
Float
Data
Address
Data
Power Down
Internal
0
0
Data
Data
Data
Data
Power Down
External
0
0
Float
Data
Data
Data
4-180
AT89C55
AT89C55
Power Down Mode
Program Memory Lock Bits
In the power down mode, the oscillator is stopped, and the
instruction that invokes power down is the last instruction
executed. The on-chip RAM and Special Function Registers retain their values until the power down mode is terminated. The only exit from power down is a hardware reset.
Reset redefines the SFRs but does not change the on-chip
RAM. The reset should not be activated before V CC is
restored to its normal operating level and must be held
active long enough to allow the oscillator to restart and stabilize.
The AT89C55 has three lock bits that can be left unprogrammed (U) or can be programmed (P) to obtain the additional features listed in the following table.
When lock bit 1 is programmed, the logic level at the EA pin
is sampled and latched during reset. If the device is powered up without a reset, the latch initializes to a random
value and holds that value until reset is activated. The
latched value of EA must agree with the current logic level
at that pin in order for the device to function properly.
Lock Bit Protection Modes
Program Lock Bits
LB1
LB2
LB3
Protection Type
1
U
U
U
No program lock features.
2
P
U
U
MOVC instructions executed from external program memory are disabled from fetching code bytes
from internal memory, EA is sampled and latched on reset, and further programming of the Flash
memory is disabled.
3
P
P
U
Same as mode 2, but verify is also disabled.
4
P
P
P
Same as mode 3, but external execution is also disabled.
Programming the Flash
The AT89C55 is normally shipped with the on-chip Flash
memory array in the erased state (that is, contents = FFH)
and ready to be programmed. The programming interface
accepts either a high-voltage (12-volt) or a low-voltage
(VCC) program enable signal. The low voltage programming
mode provides a convenient way to program the AT89C55
inside the user’s system, while the high-voltage programming mode is compatible with conventional third party
Flash or EPROM programmers.
The AT89C55 is shipped with either the high-voltage or
low-voltage programming mode enabled. The respective
top-side marking and device signature codes are listed in
following table.
Top-Side Mark
Signature
VPP = 12V
VPP = 5V
AT89C55
AT89C55
xxxx
xxxx-5
yyww
yyww
(030H) = 1EH
(030H) = 1EH
(031H) = 55H
(031H) = 55H
(032H) = FFH
(032H) = 05H
The AT89C55 code memory array is programmed byte-bybyte in either programming mode. To program any nonblank byte in the on-chip Flash Memory, the entire memory
must be erased using the Chip Erase Mode.
Programming Algorithm: Before programming the
AT89C55, the address, data and control signals should be
set up according to the Flash programming mode table and
Figures 9 and 10. To program the AT89C55, take the following steps:
1. Input the desired memory location on the address lines.
2. Input the appropriate data byte on the data lines.
3. Activate the correct combination of control signals.
4. Raise EA/VPP to 12V for the high-voltage programming
mode.
5. Pulse ALE/PROG once to program a byte in the Flash
array or the lock bits. The byte-write cycle is self-timed
and typically takes no more than 1.5 ms. Repeat steps
1 through 5, changing the address and data for the
entire array or until the end of the object file is reached.
4-181
Data Polling: The AT89C55 features Data Polling to indicate the end of a write cycle. During a write cycle, an
attempted read of the last byte written will result in the complement of the written data on PO.7. Once the write cycle
has been completed, true data is valid on all outputs, and
the next cycle may begin. Data Polling may begin any time
after a write cycle has been initiated.
Ready/Busy: The progress of byte programming can also
be monitored by the RDY/BSY output signal. P3.4 is pulled
low after ALE goes high during programming to indicate
BUSY. P3.4 is pulled high again when programming is
done to indicate READY.
Program Verify: If lock bits LB1 and LB2 have not been
programmed, the programmed code data can be read back
via the address and data lines for verification. The lock bits
cannot be verified directly. Verification of the lock bits is
achieved by observing that their features are enabled.
Chip Erase: The entire Flash array is erased electrically
by using the proper combination of control signals and by
holding ALE/PROG low for 10 ms. The code array is written
with all 1s. The chip erase operation must be executed
before the code memory can be reprogrammed.
Reading the Signature Bytes: The signature bytes are
read by the same procedure as a normal verification of
locations 030H, 031H, and 032H, except that P3.6 and
P3.7 must be pulled to a logic low. The values returned are
as follows.
(030H) = 1EH indicates manufactured by Atmel
(031H) = 55H indicates 89C55
(032H) = FFH indicates 12V programming
(032H) = 05H indicates 5V programming
Figure 9. Programming the Flash Memory
Figure 10. Verifying the Flash Memory
Programming Interface
Every code byte in the Flash array can be written, and the
entire array can be erased, by using the appropriate combination of control signals. The write operation cycle is selftimed and once initiated, will automatically time itself to
completion.
All major programming vendors offer worldwide support for
the Atmel microcontroller series. Please contact your local
programming vendor for the appropriate software revision.
+5V
+5V
AT89C55
A0 - A7
ADDR.
0000H/4FFFH
P1
P2.0 - P2.5
A8 - A13
A14*
P3.0
P2.6
SEE FLASH
PROGRAMMING
MODES TABLE
P2.7
AT89C55
VCC
P0
ALE
PGM
DATA
ADDR.
0000H/4FFFH
PROG
SEE FLASH
PROGRAMMING
MODES TABLE
P3.6
P3.7
XTAL2
EA
VI H/VPP
3-33 MHz
P1
P2.0 - P2.5
A8 - A13
A14*
P3.0
P2.6
P2.7
VCC
P0
PGM DATA
(USE 10K
PULLUPS)
ALE
P3.6
VI H
P3.7
XTAL 2
EA
XTAL 1
RST
3-33 MHz
XTAL 1
GND
RST
VI H
PSEN
*Programming address line A14 (P3.0) is not the same as the external
memory address line A14 (P2.6)
4-182
A0 - A7
AT89C55
GND
PSEN
VI H
AT89C55
Flash Programming Modes
Mode
RST
PSEN
Write Code Data
H
L
Read Code Data
H
L
H
Write Lock
Bit-1
Bit-2
Bit-3
Chip Erase
Read Signature Byte
Note:
ALE/PROG
EA/VPP
P2.6
P2.7
P3.6
P3.7
H/12V
L
H
H
H
H
L
L
H
H
L
H/12V
H
H
H
H
H
L
H/12V
H
H
L
L
H
L
H/12V
H
L
H
L
H
L
H/12V
H
L
L
L
H
L
H
L
L
L
L
H
(1)
H
1. Chip Erase requires a 10-ms PROG pulse.
4-183
Flash Programming and Verification Characteristics
TA = 0°C to 70°C, VCC = 5.0V ± 10%
Symbol
Parameter
Min
Max
Units
VPP(1)
Programming Enable Voltage
11.5
12.5
V
1.0
mA
33
MHz
IPP
(1)
Programming Enable Current
1/tCLCL
Oscillator Frequency
tAVGL
Address Setup to PROG Low
48tCLCL
tGHAX
Address Hold After PROG
48tCLCL
tDVGL
Data Setup to PROG Low
48tCLCL
tGHDX
Data Hold After PROG
48tCLCL
tEHSH
P2.7 (ENABLE) High to VPP
48tCLCL
tSHGL
VPP Setup to PROG Low
10
µs
VPP Hold After PROG
10
µs
tGLGH
PROG Width
1
tAVQV
Address to Data Valid
48tCLCL
tELQV
ENABLE Low to Data Valid
48tCLCL
tEHQZ
Data Float After ENABLE
tGHBL
PROG High to BUSY Low
1.0
µs
tWC
Byte Write Cycle Time
2.0
ms
tGHSL
Note:
4-184
(1)
1. Only used in 12-volt programming mode.
AT89C55
3
0
110
µs
48tCLCL
AT89C55
Flash Programming and Verification Waveforms - High Voltage Mode (VPP = 12V)
Flash Programming and Verification Waveforms - Low Voltage Mode (VPP = 5V)
4-185
Absolute Maximum Ratings*
Operating Temperature ................................. -55°C to +125°C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on Any Pin
with Respect to Ground .....................................-1.0V to +7.0V
Maximum Operating Voltage............................................. 6.6V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or any
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect device
reliability.
DC Output Current...................................................... 15.0 mA
DC Characteristics
The values shown in this table are valid for TA = -40°C to 85°C and VCC = 5.0V ± 20%, unless otherwise noted.
Symbol
Parameter
Condition
Min
Max
Units
VIL
Input Low Voltage
(Except EA)
-0.5
0.2 VCC - 0.1
V
VIL1
Input Low Voltage (EA)
-0.5
0.2 VCC - 0.3
V
VIH
Input High Voltage
(Except XTAL1, RST)
0.2 VCC + 0.9
VCC + 0.5
V
VIH1
Input High Voltage
(XTAL1, RST)
0.7 VCC
VCC + 0.5
V
IOL = 1.6 mA
0.45
V
IOL = 3.2 mA
0.45
V
Output Low
VOL
Voltage(1)
(Ports 1, 2, 3)
Output Low Voltage(1)
VOL1
(Port 0, ALE, PSEN)
IOH = -60 µA, VCC = 5V ± 10%
Output High Voltage
(Ports 1, 2, 3, ALE, PSEN)
VOH
2.4
V
IOH = -25 µA
0.75 VCC
V
IOH = -10 µA
0.9 VCC
V
2.4
V
IOH = -300 µA
0.75 VCC
V
IOH = -80 µA
0.9 VCC
V
IOH = -800 µA, VCC = 5V ± 10%
Output High Voltage
(Port 0 in External Bus Mode)
VOH1
IIL
Logical 0 Input Current
(Ports 1, 2, 3)
VIN = 0.45V
-50
µA
ITL
Logical 1 to 0 Transition Current (Ports 1, 2, 3)
VIN = 2V, VCC = 5V ± 10%
-650
µA
ILI
Input Leakage Current
(Port 0, EA)
0.45 < VIN < VCC
±10
µA
RRST
Reset Pulldown Resistor
300
kΩ
CIO
Pin Capacitance
Test Freq. = 1 MHz, TA = 25°C
10
pF
Active Mode, 12 MHz
25
mA
Idle Mode, 12 MHz
6.5
mA
VCC = 6V
100
µA
VCC = 3V
40
µA
50
Power Supply Current
ICC
Power Down Mode(2)
Notes:
1. Under steady state (non-transient) conditions, IOL must be externally limited as follows: Maximum IOL per port pin: 10 mA.
Maximum IOL per 8-bit port: Port 0: 26 mA, Ports 1, 2, 3: 15 mA. Maximum total IOL for all output pins: 71 mA. If IOL exceeds
the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater than the listed
test conditions.
2.
4-186
Minimum VCC for Power Down is 2V.
AT89C55
AT89C55
AC Characteristics
Under operating conditions, load capacitance for Port 0, ALE/PROG, and PSEN = 100 pF; load capacitance for all other
outputs = 80 pF.
External Program and Data Memory Characteristics
Symbol
Parameter
Variable Oscillator
Units
Min
Max
0
33
1/tCLCL
Oscillator Frequency
tLHLL
ALE Pulse Width
2tCLCL - 40
ns
tAVLL
Address Valid to ALE Low
tCLCL - 13
ns
tLLAX
Address Hold After ALE Low
tCLCL - 20
ns
tLLIV
ALE Low to Valid Instruction In
tLLPL
ALE Low to PSEN Low
tCLCL - 13
ns
tPLPH
PSEN Pulse Width
3tCLCL - 20
ns
tPLIV
PSEN Low to Valid Instruction In
tPXIX
Input Instruction Hold After PSEN
tPXIZ
Input Instruction Float After PSEN
tPXAV
PSEN to Address Valid
tAVIV
Address to Valid Instruction In
tPLAZ
PSEN Low to Address Float
tRLRH
RD Pulse Width
6tCLCL - 100
ns
tWLWH
WR Pulse Width
6tCLCL - 100
ns
tRLDV
RD Low to Valid Data In
tRHDX
Data Hold After RD
tRHDZ
Data Float After RD
2tCLCL - 28
ns
tLLDV
ALE Low to Valid Data In
8tCLCL - 150
ns
tAVDV
Address to Valid Data In
9tCLCL - 165
ns
tLLWL
ALE Low to RD or WR Low
3tCLCL - 50
3tCLCL + 50
ns
tAVWL
Address to RD or WR Low
4tCLCL - 75
ns
tQVWX
Data Valid to WR Transition
tCLCL - 20
ns
tQVWH
Data Valid to WR High
7tCLCL - 120
ns
tWHQX
Data Hold After WR
tCLCL - 20
ns
tRLAZ
RD Low to Address Float
tWHLH
RD or WR High to ALE High
4tCLCL - 65
3tCLCL - 45
0
ns
ns
ns
tCLCL - 10
tCLCL - 8
ns
ns
5tCLCL - 55
ns
10
ns
5tCLCL - 90
0
tCLCL - 20
MHz
ns
ns
0
ns
tCLCL + 25
ns
4-187
External Program Memory Read Cycle
External Data Memory Read Cycle
4-188
AT89C55
AT89C55
External Data Memory Write Cycle
External Clock Drive Waveforms
External Clock Drive
Symbol
Parameter
Min
Max
Units
1/tCLCL
Oscillator Frequency
0
33
MHz
tCLCL
Clock Period
30
ns
tCHCX
High Time
12
ns
tCLCX
Low Time
12
ns
tCLCH
Rise Time
20
ns
tCHCL
Fall Time
20
ns
4-189
Serial Port Timing: Shift Register Mode Test Conditions
The values in this table are valid for VCC = 5.0V ± 20% and Load Capacitance = 80 pF.
Symbol
Parameter
Min
tXLXL
Serial Port Clock Cycle Time
tQVXH
Max
Units
12tCLCL
ns
Output Data Setup to Clock Rising Edge
10tCLCL - 133
ns
tXHQX
Output Data Hold After Clock Rising Edge
2tCLCL - 117
ns
tXHDX
Input Data Hold After Clock Rising Edge
0
ns
tXHDV
Clock Rising Edge to Input Data Valid
10tCLCL - 133
ns
Shift Register Mode Timing Waveforms
AC Testing Input/Output Waveforms(1)
Float Waveforms(1)
Note:
Note:
4-190
1.
AC Inputs during testing are driven at VCC - 0.5V for a
logic 1 and 0.45V for a logic 0. Timing measurements
are made at VIH min. for a logic 1 and VIL max. for a
logic 0.
AT89C55
1.
For timing purposes, a port pin is no longer
floating when a 100 mV change from load voltage occurs. A port pin begins to float when a
100 mV change from the loaded VOH/VOL level
occurs.
AT89C55
Notes:
1.
XTAL1 tied to GND for ICC (power down)
2.
Lock bits programmed
4-191
Ordering Information
Speed
(MHz)
Power
Supply
Ordering Code
Package
16
5V ± 20%
AT89C55-16AA
AT89C55-16JA
AT89C55-16PA
AT89C55-16QA
44A
44J
40P6
44Q
Automotive
(-40°C to 105°C)
24
5V ± 20%
AT89C55-24AC
AT89C55-24JC
AT89C55-24PC
AT89C55-24QC
44A
44J
40P6
44Q
Commercial
(0°C to 70°C)
AT89C55-24AI
AT89C55-24JI
AT89C55-24PI
AT89C55-24QI
44A
44J
40P6
44Q
Industrial
(-40°C to 85°C)
AT89C55-33AC
AT89C55-33JC
AT89C55-33PC
AT89C55-33QC
44A
44J
40P6
44Q
Commercial
(0°C to 70°C)
33
5V ± 10%
Package Type
44A
44 Lead, Thin Plastic Gull Wing Quad Flatpack (TQFP)
44J
44 Lead, Plastic J-Leaded Chip Carrier (PLCC)
40P6
40 Lead, 0.600" Wide, Plastic Dual Inline Package (PDIP)
44Q
44 Lead, Plastic Gull Wing Quad Flatpack (PQFP)
4-192
AT89C55
Operation Range