19-5759; Rev 1; 5/11 1-Wire 4Kb EEPROM The DS24B33 is a 4096-bit, 1-Wire® EEPROM organized as 16 memory pages of 256 bits each. Data is written to a 32-byte scratchpad, verified, and then copied to the EEPROM memory. The DS24B33 communicates over a single-conductor 1-Wire bus. The communication follows the standard 1-Wire protocol. Each device has its own unalterable and unique 64-bit registration number that is factory programmed into the chip. The registration number is used to address the device in a multidrop 1-Wire net environment. The DS24B33 is software compatible to the DS2433. Applications Storage of Calibration Constants Features ♦ 4096 Bits of Nonvolatile EEPROM Partitioned Into Sixteen 256-Bit Pages ♦ Read and Write Access is Highly BackwardCompatible to the DS2433 ♦ 256-Bit Scratchpad with Strict Read/Write Protocols Ensures Integrity of Data Transfer ♦ Unique, Factory-Programmed, 64-Bit Registration Number Ensures Error-Free Device Selection and Absolute Part Identity ♦ Switchpoint Hysteresis to Optimize Performance in the Presence of Noise Board Identification ♦ Communicates to Host at 15.4kbps or 125kbps Using 1-Wire Protocol Storage of Product Revision Status ♦ Low-Cost Through-Hole and SMD Packages Typical Operating Circuit ♦ Operating Range: +2.8V to +5.25V, -40°C to +85°C ♦ IEC 1000-4-2 Level 4 ESD Protection (±8kV Contact, ±15kV Air, Typical) for IO Pin VCC Ordering Information RPUP PART IO μC DS24B33 GND TEMP RANGE PIN-PACKAGE -40°C to +85°C TO-92 DS24B33+T&R -40°C to +85°C TO-92 DS24B33S+ -40°C to +85°C 8 SO (208 mils) DS24B33S+T&R -40°C to +85°C 8 SO (208 mils) DS24B33+ +Denotes a lead(Pb)-free/RoHS-compliant package. T&R = Tape and reel. 1-Wire is a registered trademark of Maxim Integrated Products, Inc. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 DS24B33 General Description DS24B33 1-Wire 4Kb EEPROM ABSOLUTE MAXIMUM RATINGS IO Voltage Range to GND ........................................-0.5V to +6V IO Sink Current....................................................................20mA Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-55°C to +125°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) TO-92 ...........................................................................+250°C SO ................................................................................+260°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (TA = -40°C to +85°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 5.25 V 2.2 k IO PIN: GENERAL DATA 1-Wire Pullup Voltage VPUP 1-Wire Pullup Resistance (Notes 2, 3) 2.8 0.3 RPUP (Notes 2, 4) Input Capacitance CIO (Notes 5, 6) Input Load Current IL IO at VPUPMAX 0.05 5 μA High-to-Low Switching Threshold VTL (Notes 6, 7, 8) 0.5 VPUP 1.8 V Input Low Voltage VIL (Notes 2, 9) 0.5 V Low-to-High Switching Threshold VTH (Notes 6, 7, 10) 1.0 VPUP 1.0 V Switching Hysteresis VHY (Notes 6, 7, 11) 0.2 1.7 V Output Low Voltage VOL At 4mA (Note 12) 0.4 V Recovery Time (Notes 2, 13) Time-Slot Duration (Notes 2, 14) tREC t SLOT Standard speed 5 Overdrive speed 2 VPUP +4.5V 1 Directly prior to reset pulse 640μs 5 Directly prior to reset pulse > 640μs 10 Standard speed 65 Standard speed, VPUP +4.5V 61 Overdrive speed 8 Overdrive speed, VPUP +4.5V IO PIN: 1-Wire RESET, PRESENCE-DETECT CYCLE Reset Low Time (Note 2) tRSTL Presence-Detect High Time t PDH Presence-Detect Low Time t PDL Presence-Detect Sample Time (Notes 2, 15) tMSP 2 2000 pF μs μs 7 Standard speed, tREC before reset = 10μs 480 960 Standard speed, tREC before reset = 5μs Overdrive speed 480 640 48 80 Standard speed 15 60 Overdrive speed 2 6 Standard speed 60 240 Overdrive speed 8 24 Standard speed 60 75 Overdrive speed 6 10 _______________________________________________________________________________________ μs μs μs μs 1-Wire 4Kb EEPROM (TA = -40°C to +85°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS IO PIN: 1-Wire WRITE Write-Zero Low Time (Notes 2, 16) tW0L Write-One Low Time (Notes 2, 16) tW1L Standard speed 60 120 Overdrive speed 6 16 Standard speed 5 15 Overdrive speed 1 2 Standard speed 5 15 - Overdrive speed 1 2- Standard speed tRL + 15 Overdrive speed tRL + 2 μs μs IO PIN: 1-Wire READ Read Low Time (Notes 2, 17) tRL Read Sample Time (Notes 2, 17) tMSR μs μs EEPROM Programming Current I PROG (Note 18) Programming Time t PROG (Note 19) Write/Erase Cycles (Endurance) (Notes 20, 21) NCY Data Retention (Notes 22, 23, 24) tDR Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: Note 16: Note 17: Note 18: Note 19: At +25°C 200,000 At +85°C (worst case) 50,000 At +85°C (worst case) 40 2 mA 5 ms — Years Not all parameters are tested at all temperatures. System requirement. When operating near the minimum operating voltage (2.8V), a falling edge slew rate of 15V/µs or faster is recommended. Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system, 1-Wire recovery times, and current requirements during EEPROM programming. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For more heavily loaded systems, an active pullup such as that found in the DS2482-x00 or DS2480B may be required. Capacitance on the data pin could be 2500pF when VPUP is first applied. If a 2.2kΩ resistor is used to pull up the data line, then 15µs after VPUP has been applied, the parasite capacitance does not affect normal communications. Guaranteed by design, characterization, and/or simulation only. Not production tested. VTL, VTH, and VHY are a function of the internal supply voltage, which is a function of VPUP, RPUP, 1-Wire timing, and capacitive loading on IO. Lower VPUP, higher RPUP, shorter tREC, and heavier capacitive loading all lead to lower values of VTL, VTH, and VHY. Voltage below which, during a falling edge on IO, a logic 0 is detected. The voltage on IO must be less than or equal to VILMAX at all times while the master is driving IO to a logic 0 level. Voltage above which, during a rising edge on IO, a logic 1 is detected. After VTH is crossed during a rising edge on IO, the voltage on IO must drop by at least VHY to be detected as logic 0. The I-V characteristic is linear for voltages less than +1V. Applies to a single DS24B33 attached to a 1-Wire line. Defines maximum possible bit rate. Equal to 1/(tW0LMIN + tRECMIN). Interval after tRSTL during which a bus master is guaranteed to sample a logic 0 on IO if there is a DS24B33 present. Minimum limit is tPDHMAX; maximum limit is tPDHMIN + tPDLMIN. ε in Figure 11 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH. The actual maximum duration for the master to pull the line low is tW1LMAX + tF - ε and tW0LMAX + tF - ε, respectively. δ in Figure 11 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input high threshold of the bus master. The actual maximum duration for the master to pull the line low is tRLMAX + tF. Current drawn from IO during the EEPROM programming interval. The pullup circuit on IO should be such that during the programming interval, the voltage at IO is greater than or equal to VPUPMIN. If VPUP in the system is close to VPUPMIN, then a low-impedance bypass of RPUP, which can be activated during programming, may need to be added. The tPROG interval begins after the trailing rising edge on IO for the last time slot of the E/S byte for a valid copy scratchpad sequence. The interval ends once the device’s self-timed EEPROM programming cycle is complete and the current drawn by the device has returned from IPROG to IL. _______________________________________________________________________________________ 3 DS24B33 ELECTRICAL CHARACTERISTICS (continued) DS24B33 1-Wire 4Kb EEPROM ELECTRICAL CHARACTERISTICS (continued) (TA = -40°C to +85°C.) (Note 1) Write-cycle endurance is degraded as TA increases. Not 100% production tested; guaranteed by reliability monitor sampling. Data retention is degraded as TA increases. Guaranteed by 100% production test at elevated temperature for a shorter time; equivalence of this production test to data sheet limit at operating temperature range is established by reliability testing. Note 24: EEPROM writes can become nonfunctional after the data-retention time is exceeded. Long-time storage at elevated temperatures is not recommended; the device can lose its write capability after 10 years at +125°C or 40 years at +85°C. Note 20: Note 21: Note 22: Note 23: Pin Configurations TOP VIEW + N.C. 1 8 N.C. N.C. 2 7 N.C. IO 3 6 N.C. GND 4 5 N.C. DS24B33 SO (208 mils) SIDE VIEW FRONT VIEW GND 1 1 IO 2 2 N.C. 3 3 TO-92 FRONT VIEW (T&R VERSION) 1 2 3 4 _______________________________________________________________________________________ 1-Wire 4Kb EEPROM TO-92 SO NAME 1 4 GND 2 3 IO 3 1, 2, 5–8 N.C. FUNCTION Ground Reference 1-Wire Bus Interface. Open-drain pin that requires external pullup resistor. Not Connected Detailed Description The DS24B33 combines 4Kb of data EEPROM with a fully featured 1-Wire interface in a single chip. The memory is organized as 16 pages of 256 bits each. A volatile 256-bit memory page called the scratchpad acts as a buffer when writing data to the EEPROM to ensure data integrity. Data is first written to the scratchpad, from which it can be read back for verification before transferring it to the EEPROM. The operation of the DS24B33 is controlled over the single-conductor 1-Wire bus. Device communication follows the standard 1-Wire protocol. The energy required to read and write the DS24B33 is derived entirely from the 1-Wire communication line. Each DS24B33 has its own unalterable and unique 64-bit registration number. The registration number guarantees unique identification and is used to address the device in a multidrop 1-Wire net environment. Multiple DS24B33 devices can reside on a common 1-Wire bus and be operated independently of each other. Applications of the DS24B33 include calibration data storage, PCB identification, and storage of product revision status. The DS24B33 provides a high degree of backward compatibility with the DS2433, including having the same family code. Overview Figure 1 shows the relationships between the major control and memory sections of the DS24B33. The DS24B33 has four main data components: 64-bit PARASITE POWER 1-Wire NET 1-Wire FUNCTION CONTROL 64-BIT REGISTRATION NUMBER MEMORY FUNCTION CONTROL UNIT DS24B33 CRC-16 GENERATOR 32-BYTE SCRATCHPAD DATA MEMORY 16 PAGES OF 32 BYTES EACH Figure 1. Block Diagram _______________________________________________________________________________________ 5 DS24B33 Pin Description DS24B33 1-Wire 4Kb EEPROM registration number, 32-byte scratchpad, sixteen 32-byte pages of EEPROM, and a CRC-16 generator. Figure 2 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of the seven ROM (network) function commands: Read ROM, Match ROM, Search ROM, Skip ROM, Resume, Overdrive-Skip ROM, or Overdrive-Match ROM. Upon completion of an overdrive ROM command byte executed at standard speed, the device enters overdrive mode where all subsequent communication occurs at a higher speed. Figure 9 describes the protocol required for these ROM function commands. After a ROM function command is successfully executed, the memory functions become accessible and the master can provide any one of the four memory function commands. Figure 7 describes the protocol for these commands. All data is read and written least significant bit (LSB) first. Parasite Power Figure 1 shows the parasite power supply. This circuitry “steals” power whenever the IO input is high. IO provides sufficient power as long as the specified timing and voltage requirements are met. 64-Bit Registration Number Each DS24B33 contains a unique registration number that is 64 bits long. The first 8 bits are a 1-Wire family code. The next 48 bits are a unique serial number. The last 8 bits are a cyclic redundancy check (CRC) of the first 56 bits. See Figure 3 for details. The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 4. The polynomial is X8 + X5 + X4 + 1. Additional information about the 1-Wire CRC is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton® Products. DS24B33 COMMAND LEVEL: 1-Wire ROM FUNCTION COMMANDS DS24B33-SPECIFIC MEMORY FUNCTION COMMANDS AVAILABLE COMMANDS: DATA FIELD AFFECTED: READ ROM MATCH ROM SEARCH ROM SKIP ROM RESUME OVERDRIVE-SKIP ROM OVERDRIVE-MATCH ROM 64-BIT REG. #, RC-FLAG 64-BIT REG. #, RC-FLAG 64-BIT REG. #, RC-FLAG RC-FLAG RC-FLAG RC-FLAG, OD-FLAG 64-BIT REG. #, RC-FLAG, OD-FLAG WRITE SCRATCHPAD READ SCRATCHPAD COPY SCRATCHPAD READ MEMORY 32-BYTE SCRATCHPAD, FLAGS 32-BYTE SCRATCHPAD DATA MEMORY DATA MEMORY Figure 2. Hierarchical Structure for 1-Wire Protocol MSB LSB 8-BIT CRC CODE MSB 8-BIT FAMILY CODE (23h) 48-BIT SERIAL NUMBER LSB MSB LSB MSB Figure 3. 64-Bit Registration Number iButton is a registered trademark of Maxim Integrated Products, Inc. 6 _______________________________________________________________________________________ LSB 1-Wire 4Kb EEPROM The DS24B33 EEPROM array (Figure 5) consists of 16 pages of 32 bytes each, starting at address 0000h and ending at address 01FFh. In addition to the EEPROM, the device has a 32-byte volatile scratchpad. Writes to the EEPROM array are a two-step process. First, data is written to the scratchpad and then copied into the main array. The user can verify the data in the scratchpad prior to copying. POLYNOMIAL = X8 + X5 + X4 + 1 1ST STAGE X0 2ND STAGE X1 3RD STAGE X2 4TH STAGE X3 5TH STAGE X4 6TH STAGE X5 7TH STAGE X6 8TH STAGE X7 X8 INPUT DATA Figure 4. 1-Wire CRC Generator 32-BYTE INTERMEDIATE STORAGE SCRATCHPAD ADDRESS 0000h to 001Fh 32-BYTE FINAL STORAGE EEPROM PAGE 0 0020h to 003Fh 32-BYTE FINAL STORAGE EEPROM PAGE 1 0040h to 01DFh FINAL STORAGE EEPROM PAGES 2 to 14 01E0h to 01FFh 32-BYTE FINAL STORAGE EPPROM PAGE 15 Figure 5. Memory Map _______________________________________________________________________________________ 7 DS24B33 Memory The shift register bits are initialized to 0. Then, starting with the LSB of the family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, the serial number is entered. After the last bit of the serial number has been entered, the shift register contains the CRC value. Shifting in the 8 bits of the CRC returns the shift register to all 0s. DS24B33 1-Wire 4Kb EEPROM Memory Access Address Registers and Transfer Status The DS24B33 employs three address registers: TA1, TA2, and E/S (Figure 6). Registers TA1 and TA2 must be loaded with the target address to which the data is written or from which data is read. Register E/S is a read-only transfer status register used to verify data integrity with write commands. ES bits E[4:0] are loaded with the incoming T[4:0] on a Write Scratchpad command and increment on each subsequent data byte. This is, in effect, a byte-ending offset counter within the 32-byte scratchpad. Bit 5 of the E/S register, called the partial byte flag (PF), is set if the number of data bits sent by the master is not an integer multiple of 8 or if the data in the scratchpad is not valid due to a loss of power. A valid write to the scratchpad clears the PF bit. Bit 6 has no function; it always reads 0. The highest valued bit of the E/S register, called authorization accepted (AA), is valid only if the PF flag reads 0. If PF is 0 and AA is 1, the data stored in the scratchpad has already been copied to the target memory address. Writing data to the scratchpad clears this flag. Writing with Verification To write data to the DS24B33, the scratchpad must be used as intermediate storage. First, the master issues the Write Scratchpad command to specify the desired target address, followed by the data to be written to the scratchpad. Under certain conditions (see the Write Scratchpad [0Fh] section) the master receives an inverted CRC-16 of the command, address, and data at the end of the Write Scratchpad command sequence. Knowing this CRC value, the master can compare it to the value it has calculated itself to decide if the communication was successful and proceed to the Copy Scratchpad command. If the master could not receive the CRC-16, it should send the Read Scratchpad command to verify data integrity. As a preamble to the scratchpad data, the DS24B33 repeats the target address TA1 and TA2 and sends the contents of the E/S register. If the PF flag is set, data did not arrive correctly in the scratchpad or there was a loss of power since data was last written to the scratchpad. The master does not need to continue reading; it can start a new trial to write data to the scratchpad. Similarly, a set AA flag together with a cleared PF flag indicates that the device did not recognize the write command. If everything went correctly, both flags are cleared and the ending offset indicates the address of the last byte written to the scratchpad. Now the master can continue reading and verifying every data byte. After the master has verified the data, it can send the Copy Scratchpad command, for example. This command must be followed exactly by the data of the three address registers TA1, TA2, and E/S. The master should obtain the contents of these registers by reading the scratchpad. As soon as the DS24B33 has received these bytes correctly, it starts copying the scratchpad data to the requested location. BIT NUMBER 7 6 5 4 3 2 1 0 TARGET ADDRESS (TA1) T7 T6 T5 T4 T3 T2 T1 T0 TARGET ADDRESS (TA2) T15 T14 T13 T12 T11 T10 T9 T8 ENDING ADDRESS WITH DATA STATUS (E/S) (READ ONLY) AA 0 PF E4 E3 E2 E1 E0 Figure 6. Address Registers 8 _______________________________________________________________________________________ 1-Wire 4Kb EEPROM The Memory Function Flowchart (Figure 7) describes the protocols necessary for accessing the memory of the DS24B33. The target address registers TA1 and TA2 are used for both read and write. The communication between the master and the DS24B33 takes place either at standard speed (default, OD = 0) or at overdrive speed (OD = 1). If not explicitly set into the overdrive mode, the DS24B33 assumes standard speed. Write Scratchpad [0Fh] The Write Scratchpad command applies to the data memory. After issuing the Write Scratchpad command, the master must first provide the 2-byte target address, followed by the data to be written to the scratchpad. The data is written to the scratchpad starting at the byte offset of T[4:0]. The ES bits E[4:0] are loaded with the starting byte offset and increment with each subsequent byte. Effectively, E[4:0] is the byte offset of the last full byte written to the scratchpad. Only full bytes are accepted. If the last byte is incomplete, its content is ignored and PF is set. When executing the Write Scratchpad command, the CRC generator inside the DS24B33 (Figure 13) calculates a 16-bit CRC of the entire data stream, starting at the command code and ending at the last data byte as sent by the master. This CRC is generated using the CRC-16 polynomial (X16 + X15 + X2 + 1) by first clearing the CRC generator and then shifting in the command code (0Fh) of the Write Scratchpad command, the target addresses TA1 and TA2 as supplied by the master, and all the data bytes. The master can end the Write Scratchpad command at any time. However, if the end of the scratchpad is reached (E[4:0] = 11111b), the master can send 16 read time slots to receive the CRC generated by the DS24B33. The DS24B33’s memory address range is 0000h to 01FFh. If the bus master sends a target address higher than this, the DS24B33’s internal circuitry sets the 7 most significant address bits to zero as they are shifted into the internal address register. The Read Scratchpad command reveals the modified target address. The master identifies such address modifications by comparing the target address read back to the target address transmitted. If the master does not read the scratchpad, a subsequent Copy Scratchpad command does not work because the most significant bits of the target address the master sends do not match the value that the DS24B33 expects. Read Scratchpad [AAh] The Read Scratchpad command allows for verifying the target address and the integrity of the scratchpad data. After issuing the command code, the master begins reading. The first 2 bytes are the target address. The next byte is the ending offset/data status byte (E/S) followed by the scratchpad data beginning at the byte offset (T[4:0]). The master should read through the end of the scratchpad. If the master continues reading beyond the end of the scratchpad, all data are logic 1s. Copy Scratchpad [55h] The Copy Scratchpad command is used to copy data from the scratchpad to the data memory. After issuing the Copy Scratchpad command, the master must provide a 3-byte authorization pattern, which should have been obtained by an immediately preceding Read Scratchpad command. This 3-byte pattern must exactly match the data contained in the three address registers (TA1, TA2, E/S, in that order). If the pattern matches and the target address is valid, the AA flag is set and the copy begins. The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset through the ending offset is copied to memory, starting at the target address. Anywhere from 1 to 32 bytes can be copied with this command. The duration of the device’s internal data transfer is t PROG , during which the voltage on the 1-Wire bus must not fall below VPUPMIN. A pattern of alternating 0s and 1s are transmitted after the data has been copied until the master issues a reset pulse. Note: Because of the memory architecture of the DS24B33, if a Copy Scratchpad command is interrupted during the write cycle, two consecutive Copy Scratchpad commands of the same data to the same location may be necessary to recover. To verify the success of the Copy Scratchpad command, always look for the alternating 0-to-1 pattern at the end of the Copy Scratchpad command flow and also read back the EEPROM page that was to be updated. If the alternating pattern appeared and the EEPROM page data shows the intended new data, the write access was successful. No further action is required. In all other cases (alternating 0-to-1 pattern is not seen or nonmatching EEPROM page data), repeat the Write Scratchpad, Copy Scratchpad sequence until successful. _______________________________________________________________________________________ 9 DS24B33 Memory Function Commands DS24B33 1-Wire 4Kb EEPROM FROM ROM FUNCTIONS FLOWCHART (FIGURE 9) BUS MASTER Tx MEMORY FUNCTION COMMAND 0Fh WRITE SCRATCHPAD? AAh READ SCRATCHPAD? N Y BUS MASTER Rx TA1 (T[7:0]), TA2 (T[15:8]), AND E/S BYTE BUS MASTER Tx EEPROM ARRAY TARGET ADDRESS TA1 (T[7:0]), TA2 (T[15:8]) DS24B33 SETS SCRATCHPAD OFFSET = (T[4:0]) DS24B33 SETS SCRATCHPAD OFFSET = (T[4:0]) BUS MASTER Rx DATA BYTE TO SCRATCHPAD OFFSET MASTER Tx DATA BYTE TO SCRATCHPAD OFFSET DS24B33 INCREMENTS SCRATCHPAD OFFSET MASTER Tx RESET? DS24B33 SETS (E[4:0]) = SCRATCHPAD OFFSET Y N N MASTER Tx RESET? TO FIGURE 7b Y DS24B33 CLEARS PF, AA DS24B33 INCREMENTS SCRATCHPAD OFFSET N Y SCRATCHPAD OFFSET = 11111b? Y N PARTIAL BYTE? N SCRATCHPAD OFFSET = 11111b? Y N Y PF = 1 DS24B33 Tx CRC-16 OF COMMAND, ADDRESS, AND DATA BYTES AS THEY WERE SENT BY THE BUS MASTER BUS MASTER Rx "1"s N MASTER Tx RESET? Y BUS MASTER Rx "1"s N MASTER Tx RESET? Y FROM FIGURE 7b TO ROM FUNCTIONS FLOWCHART (FIGURE 9) Figure 7a. Memory Function Flowchart 10 ______________________________________________________________________________________ 1-Wire 4Kb EEPROM 55h COPY SCRATCHPAD? F0h READ MEMORY? N Y N Y BUS MASTER Tx TA1 (T[7:0]), TA2 (T[15:8]) BUS MASTER Rx TA1 (T[7:0]), TA2 (T[15:8]), AND E/S BYTE AUTHORIZATION CODE MATCH? DS24B33 FROM FIGURE 7a BUS MASTER Rx "1"s Y N N MASTER Tx RESET? Y N AA = 1 DS24B33 COPIES SCRATCHPAD DATA TO ADDRESS DS24B33 SETS MEMORY ADDRESS = (T[15:0]) * BUS MASTER Rx DATA BYTE FROM MEMORY ADDRESS DS24B33 INCREMENTS ADDRESS COUNTER DS24B33 Tx "0" Y MASTER Tx RESET? MASTER Tx RESET? N N BUS MASTER Rx "1"s Y Y ADDRESS < 1FFh? DS24B33 Tx "1" N MASTER Tx RESET? TO FIGURE 7a N MASTER Tx RESET? Y Y N BUS MASTER Rx "1"s N MASTER Tx RESET? Y *1-Wire IDLE HIGH FOR tPROG FOR POWER. Figure 7b. Memory Function Flowchart (continued) ______________________________________________________________________________________ 11 DS24B33 1-Wire 4Kb EEPROM 1-Wire Bus System Read Memory [F0h] The Read Memory command is the general function to read from the DS24B33. After issuing the command, the master must provide a 2-byte target address, which should be in the range of 0000h to 01FFh. If the target address is higher than 01FFh, the DS24B33 changes the upper 7 address bits to 0. After the address is transmitted, the master reads data starting at the (modified) target address and can continue until address 01FFh. If the master continues reading, the result is FFh. The Read Memory command can be ended at any point by issuing a reset pulse. Note that the (modified) target address provided with the Read Memory command overwrites the target address that was specified with a previously issued Write Scratchpad command. The Read Memory command overwrites the scratchpad with data from the target memory page. When reading the last byte of a memory page, the scratchpad is loaded with data from the next memory page. This could cause unexpected data to be loaded into the scratchpad. The 1-Wire bus is a system that has a single bus master and one or more slaves. In all instances the DS24B33 is a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The 1-Wire protocol defines bus transactions in terms of the bus state during specific time slots, which are initiated on the falling edge of sync pulses from the bus master. Hardware Configuration The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open-drain or three-state outputs. The 1-Wire port of the DS24B33 is open drain with an internal circuit equivalent to that shown in Figure 8. VPUP BUS MASTER DS24B33 1-Wire PORT RPUP DATA Rx Tx Rx = RECEIVE Tx = TRANSMIT OPEN-DRAIN PORT PIN Rx IL Tx 100Ω MOSFET Figure 8. Hardware Configuration 12 ______________________________________________________________________________________ 1-Wire 4Kb EEPROM Transaction Sequence The protocol for accessing the DS24B33 through the 1-Wire port is as follows: • Initialization • ROM Function Commands • Memory Function Commands • Transaction/Data Initialization All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS24B33 is on the bus and is ready to operate. For more details, see the 1-Wire Signaling section. 1-Wire ROM Function Commands Once the bus master has detected a presence, it can issue one of the seven ROM function commands that the DS24B33 supports. All ROM function commands are 8 bits long. See Figure 9 for a list of these commands. Read ROM [33h] This command allows the bus master to read the DS24B33’s 8-bit family code, unique 48-bit serial number, and 8-bit CRC. This command can only be used if there is a single slave on the bus. If more than one slave is present on the bus, a data collision occurs when all slaves try to transmit at the same time (open drain produces a wired-AND result). The resultant family code and 48-bit serial number results in a mismatch of the CRC. Match ROM [55h] The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a specific DS24B33 on a multidrop bus. Only the DS24B33 that exactly matches the 64-bit ROM sequence responds to the memory function command that follows. All other slaves wait for a reset pulse. This command can be used with a single device or multiple devices on the bus. Search ROM [F0h] When a system is initially brought up, the bus master might not know the number of devices on the 1-Wire bus or their registration numbers. By taking advantage of the bus’s wired-AND property, the master can use a process of elimination to identify the registration numbers of all slave devices. For each bit of the registration number, starting with the LSB, the bus master issues a triplet of time slots. On the first slot, each slave device participating in the search outputs the true value of its registration number bit. On the second slot, each slave device participating in the search outputs the complemented value of its registration number bit. On the third slot, the master writes the true value of the bit to be selected. All slave devices that do not match the bit written by the master stop participating in the search. If both of the read bits are zero, the master knows that slave devices exist with both states of the bit. By choosing which state to write, the bus master branches in the ROM code tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes identify the registration numbers of the remaining devices. Refer to Application Note 187: 1-Wire Search Algorithm for a detailed discussion and an example. ______________________________________________________________________________________ 13 DS24B33 A multidrop bus consists of a 1-Wire bus with multiple slaves attached. The DS24B33 supports both a standard and overdrive communication speed of 15.4kbps (maximum) and 125kbps (maximum), respectively, over the full pullup voltage range. For pullup voltages of +4.75V and higher, the DS24B33 also supports the legacy communication speed of 16.3kbps and overdrive speed of 142kbps. The slightly reduced rates for the DS24B33 are a result of additional recovery times, which in turn were driven by a 1-Wire physical interface enhancement to improve noise immunity. The value of the pullup resistor primarily depends on the network size and load conditions. The DS24B33 requires a pullup resistor of 2.2kΩ (maximum) at any speed. The idle state for the 1-Wire bus is high. If for any reason a transaction must be suspended, the bus must be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low for more than 16µs (overdrive speed) or more than 120µs (standard speed), one or more devices on the bus may be reset. DS24B33 1-Wire 4Kb EEPROM Skip ROM [CCh] This command can save time in a single-drop bus system by allowing the bus master to access the memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, a read command is issued following the Skip ROM command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns produce a wired-AND result). Resume [A5h] To maximize the data throughput in a multidrop environment, the Resume command is available. This command checks the status of the RC bit and, if it is set, directly transfers control to the memory functions, similar to a Skip ROM command. The only way to set the RC bit is by successfully executing the Match ROM, Search ROM, or Overdrive-Match ROM command. Once the RC bit is set, the device can repeatedly be accessed through the Resume command. Accessing another device on the bus clears the RC bit, preventing two or more devices from simultaneously responding to the Resume command. Overdrive-Skip ROM [3Ch] On a single-drop bus, this command can save time by allowing the bus master to access the memory functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive-Skip ROM command sets the DS24B33 in the overdrive mode (OD = 1). All communication following this command must occur at overdrive speed until a reset pulse of minimum 480µs duration resets all devices on the bus to standard speed (OD = 0). 14 When issued on a multidrop bus, this command sets all overdrive-supporting devices into overdrive mode. To subsequently address a specific overdrive-supporting device, a reset pulse at overdrive speed must be issued followed by a Match ROM or Search ROM command sequence. This speeds up the time for the search process. If more than one slave supporting overdrive is present on the bus and the Overdrive-Skip ROM command is followed by a Read command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns produce a wiredAND result). Overdrive-Match ROM [69h] The Overdrive-Match ROM command followed by a 64bit ROM sequence transmitted at overdrive speed allows the bus master to address a specific DS24B33 on a multidrop bus and to simultaneously set it in overdrive mode. Only the DS24B33 that exactly matches the 64-bit ROM sequence responds to the subsequent memory function command. Slaves already in overdrive mode from a previous Overdrive-Skip ROM or successful Overdrive-Match ROM command remain in overdrive mode. All overdrive-capable slaves return to standard speed at the next reset pulse of minimum 480µs duration. The Overdrive-Match ROM command can be used with a single device or multiple devices on the bus. ______________________________________________________________________________________ 1-Wire 4Kb EEPROM DS24B33 BUS MASTER Tx RESET PULSE FROM FIGURE 9b FROM MEMORY FUNCTIONS FLOWCHART (FIGURE 7) OD RESET PULSE? N OD = 0 Y BUS MASTER Tx ROM FUNCTION COMMAND 33h READ ROM COMMAND? DS24B33 Tx PRESENCE PULSE N 55h MATCH ROM COMMAND? F0h SEARCH ROM COMMAND? N N CCh SKIP ROM COMMAND? Y Y Y Y RC = 0 RC = 0 RC = 0 RC = 0 DS24B33Tx FAMILY CODE (1 BYTE) MASTER Tx BIT 0 TO FIGURE 9b DS24B33 Tx BIT 0 DS24B33 Tx BIT 0 MASTER Tx BIT 0 BIT 0 MATCH? N N BIT 0 MATCH? Y Y DS24B33 Tx SERIAL NUMBER (6 BYTES) N DS24B33 Tx BIT 1 MASTER Tx BIT 1 DS24B33 Tx BIT 1 MASTER Tx BIT 1 BIT 1 MATCH? N N BIT 1 MATCH? Y Y DS24B33 Tx BIT 63 DS24B33 Tx CRC BYTE MASTER Tx BIT 63 DS24B33 Tx BIT 63 MASTER Tx BIT 63 BIT 63 MATCH? N N BIT 63 MATCH? Y Y RC = 1 RC = 1 TO FIGURE 9b FROM FIGURE 9b TO MEMORY FUNCTIONS FLOWCHART (FIGURE 7) Figure 9a. ROM Functions Flowchart ______________________________________________________________________________________ 15 DS24B33 1-Wire 4Kb EEPROM TO FIGURE 9a FROM FIGURE 9a A5h RESUME COMMAND? 3Ch OVERDRIVESKIP ROM? N Y N Y N Y RC = 0; OD = 1 RC = 1? 69h OVERDRIVEMATCH ROM? RC = 0; OD = 1 N Y MASTER Tx RESET? Y MASTER Tx BIT 0 N (SEE NOTE) MASTER Tx RESET? N Y BIT 0 MATCH? N OD = 0 Y MASTER Tx BIT 1 (SEE NOTE) BIT 1 MATCH? N OD = 0 Y MASTER Tx BIT 63 (SEE NOTE) BIT 63 MATCH? N OD = 0 Y FROM FIGURE 9a RC = 1 TO FIGURE 9a NOTE: THE OD FLAG REMAINS AT 1 IF THE DEVICE WAS ALREADY AT OVERDRIVE SPEED BEFORE THE OVERDRIVE-MATCH ROM COMMAND WAS ISSUED. Figure 9b. ROM Functions Flowchart (continued) 16 ______________________________________________________________________________________ 1-Wire 4Kb EEPROM After the bus master has released the line it goes into receive mode. Now the 1-Wire bus is pulled to VPUP through the pullup resistor, or in case of a DS2482-x00 or DS2480B driver, by active circuitry. When the threshold VTH is crossed, the DS24B33 waits for tPDH and then transmits a presence pulse by pulling the line low for tPDL. To detect a presence pulse, the master must test the logical state of the 1-Wire line at tMSP. The tRSTH window must be at least the sum of tPDHMAX, t PDLMAX , and t RECMIN . Immediately after t RSTH is expired, the DS24B33 is ready for data communication. In a mixed population network, tRSTH should be extended to minimum 480µs at standard speed and 48µs at overdrive speed to accommodate other 1-Wire devices. The DS24B33 requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: reset sequence with reset pulse and presence pulse, write-zero, write-one, and read-data. Except for the presence pulse, the bus master initiates all falling edges. The DS24B33 can communicate at two different speeds: standard speed and overdrive speed. If not explicitly set into the overdrive mode, the DS24B33 communicates at standard speed. While in overdrive mode the fast timing applies to all waveforms. To get from idle to active, the voltage on the 1-Wire line needs to fall from VPUP below the threshold VTL. To get from active to idle, the voltage needs to rise from VILMAX past the threshold VTH. The time it takes for the voltage to make this rise is seen in Figure 10 as ε, and its duration depends on the pullup resistor (RPUP) used and the capacitance of the 1-Wire network attached. The voltage VILMAX is relevant for the DS24B33 when determining a logical level, not triggering any events. Figure 10 shows the initialization sequence required to begin any communication with the DS24B33. A reset pulse followed by a presence pulse indicates that the DS24B33 is ready to receive data, given the correct ROM and memory function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line for tRSTL + tF to compensate for the edge. A tRSTL duration of 480µs or longer exits the overdrive mode, returning the device to standard speed. If the DS24B33 is in overdrive mode and tRSTL is no longer than 80µs, the device remains in overdrive mode. If the device is in overdrive mode and tRSTL is between 80µs and 480µs, the device resets, but the communication speed is undetermined. Read/Write Time Slots Data communication with the DS24B33 takes place in time slots, which carry a single bit each. Write time slots transport data from bus master to slave. Read time slots transfer data from slave to master. Figure 11 illustrates the definitions of the write and read time slots. All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the threshold VTL, the DS24B33 starts its internal timing generator that determines when the data line is sampled during a write time slot and how long data is valid during a read time slot. Master-to-Slave For a write-one time slot, the voltage on the data line must have crossed the VTH threshold before the writeone low time tW1LMAX is expired. For a write-zero time slot, the voltage on the data line must stay below the VTH threshold until the write-zero low time tW0LMIN is expired. For the most reliable communication, the MASTER Tx "RESET PULSE" MASTER Rx "PRESENCE PULSE" ε tMSP VPUP VIHMASTER VTH VTL VILMAX 0V tRSTL tPDH tF tPDL tREC tRSTH RESISTOR MASTER DS24B33 Figure 10. Initialization Procedure: Reset and Presence Pulse ______________________________________________________________________________________ 17 DS24B33 1-Wire Signaling DS24B33 1-Wire 4Kb EEPROM voltage on the data line should not exceed VILMAX during the entire tW0L or tW1L window. After the VTH thresh- old has been crossed, the DS24B33 needs a recovery time tREC before it is ready for the next time slot. WRITE-ONE TIME SLOT tW1L VPUP VIHMASTER VTH VTL VILMAX 0V ε tF tSLOT RESISTOR MASTER WRITE-ZERO TIME SLOT tW0L VPUP VIHMASTER VTH VTL VILMAX 0V ε tF tREC tSLOT RESISTOR MASTER READ-DATA TIME SLOT tMSR tRL VPUP VIHMASTER VTH MASTER SAMPLING WINDOW VTL VILMAX 0V δ tF tREC tSLOT RESISTOR MASTER DS24B33 Figure 11. Read/Write Timing Diagrams 18 ______________________________________________________________________________________ 1-Wire 4Kb EEPROM Improved Network Behavior (Switchpoint Hysteresis) In a 1-Wire environment, line termination is possible only during transients controlled by the bus master (1-Wire driver). 1-Wire networks, therefore, are susceptible to noise of various origins. Depending on the physical size and topology of the network, reflections from end points and branch points can add up or cancel each other to some extent. Such reflections are visible as glitches or ringing on the 1-Wire communication line. VPUP VTH VHY 0V Figure 12. Hysteresis at the Low-to-High Switching Threshold Noise coupled onto the 1-Wire line from external sources can also result in signal glitching. A glitch during the rising edge of a time slot can cause a slave device to lose synchronization with the master and, consequently, result in a Search ROM command coming to a dead end or cause a device-specific function command to abort. For better performance in network applications, the DS24B33 uses an improved 1-Wire front-end, which makes it less sensitive to noise. The 1-Wire front-end of the DS24B33 differs from traditional slave devices in one characteristic: There is a hysteresis at the low-to-high switching threshold VTH. If a negative glitch crosses V TH but does not go below VTH - VHY, it is not recognized (Figure 12). The hysteresis is effective at any 1-Wire speed. CRC Generation The DS24B33 uses two different types of CRCs. One CRC is an 8-bit type and is stored in the most significant byte of the 64-bit registration number. The bus master can compute a CRC value from the first 56 bits of the 64-bit registration number and compare it to the value stored within the DS24B33 to determine if the registration number has been received error-free. The equivalent polynomial function of this CRC is X8 + X5 + X4 + 1. This 8-bit CRC is received in the true (noninverted) form. It is computed and programmed into the chip at the factory. The other CRC is a 16-bit type, generated according to the standardized CRC-16 polynomial function X16 + X15 + X2 + 1. This CRC is used for fast verification of a data transfer when writing to the scratchpad. In contrast to the 8-bit CRC, the 16-bit CRC is always communicated in the inverted form. A CRC generator inside the DS24B33 (Figure 13) calculates a new 16-bit CRC, as shown in the command flowchart (Figure 7). The bus master compares the CRC value read from the device to the one it calculates from the data, and decides whether to continue with an operation. With the Write Scratchpad command, the CRC is generated by first clearing the CRC generator and then shifting in the command code, the target addresses TA1 and TA2, and all the data bytes as they were sent by the bus master. The DS24B33 transmits this CRC only if the data bytes written to the scratchpad include scratchpad ending offset 11111b. The data can start at any location within the scratchpad. For more information on generating CRC values refer to Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products. ______________________________________________________________________________________ 19 DS24B33 Slave-to-Master A read-data time slot begins like a write-one time slot. The voltage on the data line must remain below VTL until the read low time tRL is expired. During the tRL window, when responding with a 0, the DS24B33 starts pulling the data line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again. When responding with a 1, the DS24B33 does not hold the data line low at all, and the voltage starts rising as soon as tRL is over. The sum of tRL + δ (rise time) on one side and the internal timing generator of the DS24B33 on the other side define the master sampling window (t MSRMIN to tMSRMAX) in which the master must perform a read from the data line. For the most reliable communication, tRL should be as short as permissible, and the master should read close to but no later than tMSRMAX. After reading from the data line, the master must wait until tSLOT is expired. This guarantees sufficient recovery time tREC for the DS24B33 to get ready for the next time slot. Note that tREC specified herein applies only to a single DS24B33 attached to a 1-Wire line. For multidevice configurations, t REC needs to be extended to accommodate the additional 1-Wire device input capacitance. Alternatively, an interface that performs active pullup during the 1-Wire recovery time such as the DS2482-x00 or DS2480B 1-Wire line drivers can be used. DS24B33 1-Wire 4Kb EEPROM POLYNOMIAL = X16 + X15 + X2 + 1 1ST STAGE 3RD STAGE 2ND STAGE X0 X2 X1 9TH STAGE X8 10TH STAGE X9 11TH STAGE X10 4TH STAGE X3 12TH STAGE X11 5TH STAGE 6TH STAGE X4 13TH STAGE X12 X5 14TH STAGE X13 7TH STAGE X6 8TH STAGE X7 15TH STAGE X14 16TH STAGE X15 X16 CRC OUTPUT INPUT DATA Figure 13. CRC-16 Hardware Description and Polynomial Command-Specific 1-Wire Communication Protocol—Legend SYMBOL RST 1-Wire reset pulse generated by master PD 1-Wire presence pulse generated by slave Select Command and data to satisfy the ROM function protocol WS Command: “Write Scratchpad” RS Command: “Read Scratchpad” CPS Command: “Copy Scratchpad” RM Command: “Read Memory” TA Target Address TA1, TA2 TA-E/S <data to EOS> <data to EOM> Target Address TA1, TA2 with E/S byte Transfer of as many bytes as needed to reach the end of the scratchpad for a given target address Transfer of as many bytes as are needed to reach the end of the memory CRC-16 Transfer of an inverted CRC-16 FF loop Indefinite loop where the master reads FF bytes AA loop Indefinite loop where the master reads AA bytes Programming 20 DESCRIPTION Data transfer to EEPROM; no activity on the 1-Wire bus permitted during this time ______________________________________________________________________________________ 1-Wire 4Kb EEPROM Master-to-Slave Slave-to-Master Programming 1-Wire Communication Examples Write Scratchpad, Reaching the End of the Scratchpad RST PD Select WS TA <data to EOS> CRC-16 FF loop Read Scratchpad RST PD Select RS TA-E/S <data to EOS> FF loop Copy Scratchpad (Success) RST PD Select CPS TA-E/S Programming AA loop Copy Scratchpad (Fail TA-E/S) RST PD Select CPS TA-E/S FF loop Read Memory RST PD Select RM TA <data to EOM> FF loop Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 SO W8+2 21-0262 90-0258 3 TO-92 (Bulk) Q3+1 21-0248 — 3 TO-92 (T&R) Q3+1 21-0250 — ______________________________________________________________________________________ 21 DS24B33 Command-Specific 1-Wire Communication Protocol—Color Codes DS24B33 1-Wire 4Kb EEPROM Revision History REVISION NUMBER REVISION DATE 0 2/11 Initial release — 1 5/11 Implemented text changes to better market the document 1 DESCRIPTION PAGES CHANGED Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.