Dallas DS2506 64-kbit add-only memory Datasheet

DS2506
64-kbit Add-Only Memory
www.dalsemi.com
PR-35
DALLAS
DS2506
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1
8
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2
7
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DATA
3
6
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GND
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5
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8-PIN SOIC
(208 mil)
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65536 bits Electrically Programmable Read
Only Memory (EPROM) communicates with
the economy of one signal plus ground
Unique, factory-lasered and tested 64-bit
registration number (8-bit family code +
48-bit serial number + 8-bit CRC tester)
assures absolute traceability because no two
parts are alike
Built-in multidrop controller ensures
compatibility with other MicroLAN products
EPROM partitioned into two hundred fifty six
256-bit pages for randomly accessing
packetized data records
Each memory page can be permanently writeprotected to prevent tampering
Device is an “add only” memory where
additional data can be programmed into
EPROM without disturbing existing data
Architecture allows software to patch data by
superseding an old page in favor of a newly
programmed page
Reduces control, address, data, power, and
programming signals to a single data pin
Directly connects to a single port pin of a
microprocessor and communicates at up to
16.3 kbits per second
Overdrive mode boosts communication speed
to 142 kbits per second
8-bit family code specifies DS2506
communications requirements to reader
Presence detector acknowledges when the
reader first applies voltage
Low cost PR35 or 8-pin SOIC surface mount
package
Reads over a wide voltage range of 2.8V to
6.0V from -40°C to +85°C; programs at
11.5V to 12.0V from -40°C to +50°C
GND
PIN ASSIGNMENT
DATA
FEATURES
1 2 3
Bottom View
See Mech.
Drawings Section
ORDERING INFORMATION
DS2506
DS2506S
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PR35 Package
8-Pin SOIC Package
062100
DS2506
SILICON LABEL DESCRIPTION
The DS2506 64 kbits Add-Only Memory identifies and stores relevant information about the product to
which it is associated. This lot or product specific information can be accessed with minimal interface, for
example a single port pin of a microcontroller. The DS2506 consists of a factory-lasered registration
number that includes a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (0FH) plus
64 kbits of user-programmable EPROM. The power to program and read the DS2506 is derived entirely
from the 1-Wire communication line. Data is transferred serially via the 1-Wire protocol which requires
only a single data lead and a ground return. The entire device can be programmed and then writeprotected if desired. Alternatively, the part may be programmed multiple times with new data being
appended to, but not overwriting, existing data with each subsequent programming of the device. Note:
Individual bits can be changed only from a logical 1 to a logical 0, never from a logical 0 to a logical 1. A
provision is also included for indicating that a certain page or pages of data are no longer valid and have
been replaced with new or updated data that is now residing at an alternate page address. This page
address redirection allows software to patch data and enhance the flexibility of the device as a stand-alone
database. The 48-bit serial number that is factory-lasered into each DS2506 provides a guaranteed unique
identity which allows for absolute traceability. The PR35 and SOIC packages provide a compact
enclosure that allows standard assembly equipment to handle the device easily for attachment to printed
circuit boards or wiring. Typical applications include storage of calibration constants, maintenance
records, asset tracking, product revision status and access codes.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS2506. The DS2506 has three main data components: 1) 64-bit lasered ROM, 2) 65536-bits
EPROM Data Memory, and 3) 2816-bits EPROM Status Memory. The device derives its power for read
operations entirely from the 1-Wire communication line by storing energy on an internal capacitor during
periods of time when the signal line is high and continues to operate off of this “parasite” power source
during the low times of the 1-Wire line until it returns high to replenish the parasite (capacitor) supply.
During programming, 1-Wire communication occurs at normal voltage levels and then is pulsed
momentarily to the programming voltage to cause the selected EPROM bits to be programmed. The
1-Wire line must be able to provide 12 volts and 10 milliamperes to adequately program the EPROM
portions of the part. Whenever programming voltages are present on the 1-Wire line a special high
voltage detect circuit within the DS2506 generates an internal logic signal to indicate this condition. The
hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one
of the six ROM Function Commands, 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM, 5)
Overdrive-Skip ROM or 6) Overdrive-Match ROM. Upon completion of an Overdrive ROM command
byte executed at regular speed, the device will enter the Overdrive mode where all subsequent
communication occurs at a higher speed. These commands operate on the 64-bit lasered ROM portion of
each device and can singulate a specific device if many are present on the 1-Wire line as well as indicate
to the bus master how many and what types of devices are present. The protocol required for these ROM
Function Commands is described in Figure 8. After a ROM Function Command is successfully executed,
the memory functions that operate on the EPROM portions of the DS2506 become accessible and the bus
master may issue any one of the five Memory Function Commands specific to the DS2506 to read or
program the various data fields. The protocol for these Memory Function Commands is described in
Figure 5. All data is read and written least significant bit first.
64-BIT LASERED ROM
Each DS2506 contains a unique ROM code 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 CRC of the first 56 bits. (See Figure 3).
The 64-bit ROM and ROM Function Control section allow the DS2506 to operate as a 1-Wire device and
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DS2506
follow the 1-Wire protocol detailed in the section “1-Wire Bus System.” The memory functions required
to read and program the EPROM sections of the DS2506 are not accessible until the ROM function
protocol has been satisfied. This protocol is described in the ROM functions flow chart (Figure 8). The
1-Wire bus master must first provide one of six ROM function commands: 1) Read ROM, 2) Match
ROM, 3) Search ROM, 4) Skip ROM, 5) Overdrive-Skip ROM or 6) Overdrive-Match ROM. After a
ROM function sequence has been successfully executed, the bus master may then provide any one of the
memory function commands specific to the DS2506 (Figure 5).
The 1-Wire CRC of the lasered ROM is generated using the polynomial X8 + X5 + X4 + 1. Additional
information about the Dallas Semiconductor 1-Wire Cyclic Redundancy Check is available in the Book
of DS19xx iButton Standards. The shift register acting as the CRC accumulator is initialized to zero.
Then starting with the least significant bit of the family code, 1 bit at a time is shifted in. After the 8th bit
of the family code has been entered, then the serial number is entered. After the 48th bit of the serial
number has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC should
return the shift register to all zeroes.
DS2506 BLOCK DIAGRAM Figure 1
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DS2506
HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2
64-BIT LASERED ROM Figure 3
8-Bit CRC Code
MSB
48-Bit Serial Number
LSB MSB
8-Bit Family Code (0FH)
LSB MSB
LSB
65536-BITS EPROM
The memory map in Figure 4 shows the 65536-bit EPROM section of the DS2506 which is configured as
256 pages of 32 bytes each. The 8-bit scratchpad is an additional register that acts as a buffer when
programming the memory. Data is first written to the scratchpad and then verified by reading an 16-bit
CRC from the DS2506 that confirms proper receipt of the data and address. If the buffer contents are
correct, a programming voltage should be applied and the byte of data will be written into the selected
address in memory. This process insures data integrity when programming the memory. The details for
reading and programming the 65536-bit EPROM portion of the DS2506 are given in the Memory
Function Commands section.
EPROM STATUS BYTES
In addition to the 65536 bits of data memory the DS2506 provides 2816 bits of Status Memory accessible
with separate commands.
The EPROM Status Bytes can be read or programmed to indicate various conditions to the software
interrogating the DS2506. The first 32 bytes of the EPROM Status Memory (addresses 000 to 01FH)
contain the Write Protect Page bits which inhibit programming of the corresponding page in the 65536-bit
main memory area if the appropriate write protection bit is programmed. Once a bit has been
programmed in the Write Protect Page section of the Status Memory, the entire 32 byte page that
corresponds to that bit can no longer be altered but may still be read.
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DS2506
The next 32 bytes of the EPROM Status Memory (addresses 020 to 03FH) contain the Write Protect bits
which inhibit altering the Page Address Redirection Byte corresponding to each page in the 65536-bit
main memory area.
The following 32 bytes within the EPROM Status Memory (addresses 040 to 05FH) are reserved for use
by the iButton operating software TMEX. Their purpose is to indicate which memory pages are already in
use. Originally, all of these bits are unprogrammed, indicating that the device does not store any data. As
soon as data is written to any page of the device under control of TMEX, the bit inside this bitmap
corresponding to that page will be programmed to 0, marking this page as used. These bits are application
flags only and have no impact on the internal logic of the DS2506.
The next 256 bytes of the EPROM Status Memory (addresses 100H to 1FFH) contain the Page Address
Redirection Bytes which indicate if one or more of the pages of data in the 65536-bit EPROM section
have been invalidated by software and redirected to the page address contained in the appropriate
redirection byte. The hardware of the DS2506 makes no decisions based on the contents of the Page
Address Redirection Bytes. Since with EPROM technology bits can only be changed from a logical 1 to
a logical 0 by programming, it is not possible to simply rewrite a page if the data requires changing or
updating. But with space permitting, an entire page of data can be redirected to another page within the
DS2506. Under TMEX a page is redirected by writing the one’s complement of the new page address
into the Page Address Redirection Byte that corresponds to the original (replaced) page. This architecture
allows the user’s software to make a “data patch” to the EPROM by indicating that a particular page or
pages should be replaced with those indicated in the Page Address Redirection Bytes. To leave an
authentic audit trail of data patches, it is recommended to also program the write protect bit of the Page
Address Redirection Byte, after the page redirection is programmed. Without this protection, it is still
possible to modify the Page Address Redirection Byte, making it point to a different memory page than
the true one.
If a Page Address Redirection Byte has a FFH value, the data in the main memory that corresponds to
that page is valid. If a Page Address Redirection Byte has some other hex value than FFH, the data in the
page corresponding to that redirection byte is invalid. According to the TMEX definitions the valid data
can now be found at the one’s complement of the page address indicated by the hex value stored in the
associated Page Address Redirection Byte. A value of FDH in the redirection byte for page 1, for
example, would indicate that the updated data is now in page 2. The status memory is programmed
similarly to the data memory. Details for reading and programming the EPROM status memory portion of
the DS2506 are given in the Memory Function Commands section.
The Status Memory address range of the DS2506 extends from 000 to 1FFH. The memory locations 60H
to 0FFH and 200H and higher are physically not implemented. Reading these locations will usually
result in FFH bytes. Attempts to write to these locations will be ignored.
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DS2506
DS2506 MEMORY MAP Figure 4
STATUS MEMORY MAP
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DS2506
MEMORY FUNCTION COMMANDS
The “Memory Function Flow Chart” (Figure 5) describes the protocols necessary for accessing the
various data fields within the DS2506. The Memory Function Control section, 8-bit scratchpad, and the
Program Voltage Detect circuit combine to interpret the commands issued by the bus master and create
the correct control signals within the device. A three byte protocol is issued by the bus master. It is
comprised of a command byte to determine the type of operation and two address bytes to determine the
specific starting byte location within a data field. The command byte indicates if the device is to be read
or written. Writing data involves not only issuing the correct command sequence but also providing a
12-volt programming voltage at the appropriate times. To execute a write sequence, a byte of data is first
loaded into the scratchpad and then programmed into the selected address. Write sequences always occur
a byte at a time. To execute a read sequence, the starting address is issued by the bus master and data is
read from the part beginning at that initial location and continuing to the end of the selected data field or
until a reset sequence is issued. All bits transferred to the DS2506 and received back by the bus master
are sent least significant bit first.
READ MEMORY [F0H]
The Read Memory command is used to read data from the 65536 bits EPROM data field. The bus master
follows the command byte with a two byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a
starting byte location within the data field. With every subsequent read data time slot the bus master
receives data from the DS2506 starting at the initial address and continuing until the end of the 65536 bits
data field is reached or until a Reset Pulse is issued. If reading occurs through the end of memory space,
the bus master may issue sixteen additional read time slots and the DS2506 will respond with a 16-bit
CRC of the command, address bytes and all data bytes read from the initial starting byte through the last
byte of memory. This CRC is the result of clearing the CRC generator and then shifting in the command
byte followed by the two address bytes and the data bytes beginning at the first addressed memory
location and continuing through to the last byte of the EPROM data memory. After the CRC is received
by the bus master, any subsequent read time slots will appear as logical 1s until a Reset Pulse is issued.
Any reads ended by a Reset Pulse prior to reaching the end of memory will not have the 16-bit CRC
available.
Typically a 16-bit CRC would be stored with each page of data to insure rapid, error-free data transfers
that eliminate having to read a page multiple times to determine if the received data is correct or not. (See
Book of DS19xx iButton Standards, Chapter 7 for the recommended file structure to be used with the 1Wire environment). If CRC values are imbedded within the data, a Reset Pulse may be issued at the end
of memory space during a Read Memory command.
READ STATUS [AAH]
The Read Status command is used to read data from the EPROM Status data field. The bus master
follows the command byte with a two byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a
starting byte location within the data field. With every subsequent read data time slot the bus master
receives data from the DS2506 starting at the supplied address and continuing until the end of an eight
byte page of the EPROM Status data field is reached. At that point the bus master will receive a 16-bit
CRC of the command byte, address bytes and status data bytes. This CRC is computed by the DS2506
and read back by the bus master to check if the command word, starting address and data were received
correctly. If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and the entire
sequence must be repeated.
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DS2506
Note that the initial pass through the Read Status flow chart will generate a 16-bit CRC value that is the
result of clearing the CRC generator and then shifting in the command byte followed by the two address
bytes, and finally the data bytes beginning at the first addressed memory location and continuing through
to the last byte of the addressed EPROM Status data page. The last byte of a Status data page always has
an ending address of xx7 or xxFH. Subsequent passes through the Read Status flow chart will generate a
16-bit CRC that is the result of clearing the CRC generator and then shifting in the new data bytes starting
at the first byte of the next page of the EPROM Status data field.
This feature is provided since the EPROM Status information may change over time making it impossible
to program the data once and include an accompanying CRC that will always be valid. Therefore, the
Read Status command supplies a 16-bit CRC that is based on and always is consistent with the current
data stored in the EPROM Status data field.
MEMORY FUNCTION FLOW CHART Figure 5
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DS2506
MEMORY FUNCTION FLOW CHART Figure 5 (cont’d)
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DS2506
MEMORY FUNCTION FLOW CHART Figure 5 (cont’d)
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DS2506
After the 16-bit CRC of the last EPROM Status data page is read, the bus master will receive logical 1s
from the DS2506 until a Reset Pulse is issued. The Read Status command sequence can be ended at any
point by issuing a Reset Pulse.
EXTENDED READ MEMORY [A5H]
The Extended Read Memory command supports page redirection when reading data from the 65536-bit
EPROM data field. One major difference between the Extended Read Memory and the basic Read
Memory command is that the bus master receives the Redirection Byte first before investing time in
reading data from the addressed memory location. This allows the bus master to quickly decide whether
to continue and access the data at the selected starting page or to terminate and restart the reading process
at the redirected page address. A non-redirected page is identified by a Redirection Byte with a value of
FFH (see description of EPROM Status Bytes). If the Redirection Byte is different than this, the master
has to complement it to obtain the new page number. Multiplying the page number by 32 (20H) results in
the new address the master has to send to the DS2506 to read the updated data replacing the old data.
There is no logical limitation in the number of redirections of any page. The only limit is the number of
available memory pages within the DS2506.
In addition to page redirection, the Extended Read Memory command also supports “bit-oriented”
applications where the user cannot store a 16-bit CRC with the data itself. With bit-oriented applications
the EPROM information may change over time within a page boundary making it impossible to include
an accompanying CRC that will always be valid. Therefore, the Extended Read Memory command
concludes each page with the DS2506 generating and supplying a 16-bit CRC that is based on and
therefore always consistent with the current data stored in each page of the 65536-bit EPROM data field.
After having sent the command code of the Extended Read Memory command, the bus master follows
the command byte with a two byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a starting byte
location within the data field. By sending eight read data time slots, the master receives the Redirection
Byte associated with the page given by the starting address. With the next sixteen read data time slots,
the bus master receives a 16-bit CRC of the command byte, address bytes and the Redirection Byte. This
CRC is computed by the DS2506 and read back by the bus master to check if the command word, starting
address and Redirection Byte were received correctly.
If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and the entire sequence must
be repeated. If the CRC received by the bus master is correct, the bus master issues read time slots and
receives data from the DS2506 starting at the initial address and continuing until the end of a 32 byte
page is reached. At that point the bus master will send sixteen additional read time slots and receive a
16-bit CRC that is the result of shifting into the CRC generator all of the data bytes from the initial
starting byte to the last byte of the current page.
With the next 24 read data time slots the master will receive the Redirection Byte of the next page
followed by a 16-bit CRC of the Redirection Byte. After this, data is again read from the 65536-bit
EPROM data field starting at the beginning of the new page. This sequence will continue until the final
page and its accompanying CRC are read by the bus master. The Extended Read Memory command
provides a 16-bit CRC at two locations within the transaction flow chart: 1) after the Redirection Byte
and 2) at the end of each memory page. The CRC at the end of the memory page is always the result of
clearing the CRC generator and shifting in the data bytes beginning at the first addressed memory
location of the EPROM data page until the last byte of this page. With the initial pass through the
Extended Read Memory flow chart the 16-bit CRC value is the result of shifting the command byte into
the cleared CRC generator, followed by the two address bytes and the Redirection Byte. Subsequent
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DS2506
passes through the Extended Read Memory flow chart will generate a 16-bit CRC that is the result of
clearing the CRC generator and then shifting in the Redirection Byte only.
After the 16-bit CRC of the last page is read, the bus master will receive logical 1s from the DS2506 until
a Reset Pulse is issued. The Extended Read Memory command sequence can be exited at any point by
issuing a Reset Pulse.
WRITING EPROM MEMORY
The DS2506 has two independent EPROM memory fields, Data Memory and Status Memory. The
function flow for writing either field is almost identical. After the appropriate write command has been
issued, the bus master will send a two byte starting address (TA1=(T7:T0), TA2=(T15:T8)) and a byte of
data (D7:D0). A 16-bit CRC of the command byte, address bytes, and data byte is computed by the
DS2506 and read back by the bus master to confirm that the correct command word, starting address, and
data byte were received.
If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and the entire sequence must
be repeated. If the CRC received by the bus master is correct, a programming pulse (12 volts on the
1-Wire bus for 480 µs) is issued by the bus master. Prior to programming, the entire EPROM memory
field will appear as logical 1s. For each bit in the data byte provided by the bus master that is set to a
logical 0, the corresponding bit in the selected byte of the EPROM memory is programmed to a logical 0
after the programming pulse has been applied.
After the 480 µs programming pulse is applied and the data line returns to the idle level (5 volts), the bus
master issues eight read time slots to verify that the appropriate bits have been programmed. The DS2506
responds with the data from the selected EPROM address sent least significant bit first. This byte contains
the bit-wise logical AND of all data ever written to this address. If the EPROM byte contains 1s in bit
positions where the byte issued by the master contained 0s, a Reset Pulse should be issued and the current
byte address should be programmed again. If the DS2506 EPROM byte contains 0s in the same bit
positions as the data byte, the programming was successful and the DS2506 will automatically increment
its address counter to select the next byte in the EPROM memory field. The new two byte address will
also be loaded into the 16-bit CRC generator as a starting value. The bus master will issue the next byte
of data using eight write time slots.
As the DS2506 receives this byte of data into the scratchpad, it also shifts the data into the CRC generator
that has been preloaded with the current address and the result is a 16-bit CRC of the new data byte and
the new address. After supplying the data byte, the bus master will read this 16-bit CRC from the DS2506
with sixteen read time slots to confirm that the address incremented properly and the data byte was
received correctly. If the CRC is incorrect, a Reset Pulse must be issued and the write sequence must be
restarted. If the CRC is correct, the bus master will issue a programming pulse and the selected byte in
memory will be programmed.
Note that the initial pass through the write flow chart will generate an 16-bit CRC value that is the result
of shifting the command byte into the CRC generator, followed by the two address bytes, and finally the
data byte. Subsequent passes through the write flow chart due to the DS2506 automatically incrementing
its address counter will generate a 16-bit CRC that is the result of loading (not shifting) the new
(incremented) address into the CRC generator and then shifting in the new data byte.
For both of these cases, the decision to continue (to apply a program pulse to the DS2506) is made
entirely by the bus master, since the DS2506 will not be able to determine if the 16-bit CRC calculated by
the bus master agrees with the 16-bit CRC calculated by the DS2506. If an incorrect CRC is ignored and
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DS2506
a program pulse is applied by the bus master, incorrect programming could occur within the DS2506.
Also note that the DS2506 will always increment its internal address counter after the receipt of the eight
read time slots used to confirm the programming of the selected EPROM byte. The decision to continue
is again made entirely by the bus master. Therefore if the EPROM data byte does not match the supplied
data byte but the master continues with the write command, incorrect programming could occur within
the DS2506. The write command sequence can be ended at any point by issuing a Reset Pulse.
WRITE MEMORY [0FH]/SPEED WRITE MEMORY [F3H]
The Write Memory command is used to program the 65536-bit EPROM data field. The details of the
functional flow chart are described in the section “WRITING EPROM MEMORY.”
The data memory address range is 0000H to 1FFFH. If the bus master sends a starting address higher than
this, the three most significant address bits are set to zeros by the internal circuitry of the chip. This will
result in a mismatch between the CRC calculated by the DS2506 and the CRC calculated by the bus
master, indicating an error condition.
To save time when writing more than one consecutive byte of the DS2506’s data memory it is possible to
omit reading the 16-bit CRC which allows verification of data and address before the data is copied to the
EPROM memory. At regular speed this saves 16 time slots or 976 µs for every byte to be programmed.
This speed-programming mode is accessed with the command code F3H instead of 0FH. It follows
basically the same flow chart as the Write Memory command, but skips sending the CRC immediately
preceding the program pulse. This command should only be used if the electrical contact between bus
master and the DS2506 is firm since a poor contact may result in corrupted data inside the EPROM
memory.
WRITE STATUS [55H]/SPEED WRITE STATUS [F5H]
The Write Status command is used to program the 2816-bit EPROM Status Memory field. The details of
the functional flow chart are described in the section “WRITING EPROM MEMORY.”
The Status Memory address range is 0000H to 01FFH. Attempts to write to the not implemented status
memory locations will be ignored. If the bus master sends a starting address higher than 1FFFH, the three
most significant address bits are set to zeros by the internal circuitry of the chip. This will result in a
mismatch between the CRC calculated by the DS2506 and the CRC calculated by the bus master,
indicating an error condition. To save time when writing more than one consecutive byte of the
DS2506’s status memory it is possible to omit reading the 16-bit CRC which allows verification of data
and address before the data is copied to the EPROM memory. At regular speed this saves 16 time slots or
976 µs for every byte to be programmed. This speed-programming mode is accessed with the command
code F5H instead of 55H. It follows basically the same flow chart as the Write Status command, but skips
sending the CRC immediately preceding the program pulse. This command should only be used if the
electrical contact between bus master and the DS2506 is firm since a poor contact may result in corrupted
data inside the EPROM status memory.
1-WIRE BUS SYSTEM
The 1-Wire bus is a system which has a single bus master and one or more slaves. In all instances, the
DS2506 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
signalling (signal type and timing). A 1-Wire protocol defines bus transactions in terms of the bus state
during specified time slots that are initiated on the falling edge of sync pulses from the bus master. For a
more detailed protocol description, refer to Chapter 4 of the Book of DS19xx iButton Standards.
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DS2506
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 an
open drain connection or 3-state outputs. The DS2506 is an open drain part with an internal circuit
equivalent to that shown in Figure 6. The bus master can be the same equivalent circuit. If a bi-directional
pin is not available, separate output and input pins can be tied together.
The bus master requires a pullup resistor at the master end of the bus, with the bus master circuit
equivalent to the one shown in Figures 7a and 7b. The value of the pullup resistor should be
approximately 5 kΩ for short line lengths.
A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At regular speed the 1-Wire bus
has a maximum data rate of 16.3 kbits per second. The speed can be boosted to 142 kbits per second by
activating the Overdrive mode. If the bus master is also required to perform programming of the EPROM
portions of the DS2506, a programming supply capable of delivering up to 10 milliamps at 12 volts for
480 µs is required. The idle state for the 1-Wire bus is high. If, for any reason, a transaction needs to 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 16 µs (overdrive speed) or more than 120 µs (regular speed), one or more
of the devices on the bus may be reset.
Transaction Sequence
The sequence for accessing the DS2506 via the 1-Wire port is as follows:
Initialization
ROM Function Command
Memory Function Command
Read/Write Memory/Status
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 a presence pulse(s) transmitted by the
slave(s).
The presence pulse lets the bus master know that the DS2506 is on the bus and is ready to operate. For
more details, see the “1-Wire Signalling” section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the six ROM function commands. All
ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure
8):
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DS2506
Read ROM [33H]
This command allows the bus master to read the DS2506’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command can be used only if there is a single DS2506 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open drain will produce a wired-AND result). The resultant family code and 48-bit serial number
will usually result 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 DS2506 on a multidrop bus. Only the DS2506 that exactly matches the 64-bit ROM sequence
will respond to the subsequent memory function command. All slaves that do not match the 64-bit ROM
sequence will wait for a reset pulse. This command can be used with a single or multiple devices on the
bus.
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 a read command is issued following the Skip ROM command, data collision will occur on the bus as
multiple slaves transmit simultaneously (open drain pulldowns will produce a wired-AND result).
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 64-bit ROM codes. The search ROM command allows the bus master to use a process
of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The ROM search process
is the repetition of a simple 3-step routine: read a bit, read the complement of the bit, then write the
desired value of that bit. The bus master performs this simple, 3-step routine on each bit of the ROM.
After one complete pass, the bus master knows the contents of the ROM in one device. The remaining
number of devices and their ROM codes may be identified by additional passes. See Chapter 5 of the
Book of DS19xx iButton Standards for a comprehensive discussion of a ROM search, including an actual
example.
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DS2506
DS2506 EQUIVALENT CIRCUIT Figure 6
BUS MASTER CIRCUIT Figure 7
16 of 25
DS2506
ROM FUNCTIONS FLOW CHART Figure 8
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DS2506
ROM FUNCTIONS FLOW CHART Figure 8 (cont’d)
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DS2506
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 sets the DS2506 in the Overdrive Mode (OD=1). All communication following this command
has to occur at Overdrive Speed until a reset pulse of minimum 480 µs duration resets all devices on the
bus to regular speed (OD=0).
When issued on a multidrop bus this command will set all Overdrive-capable devices into Overdrive
mode. To subsequently address a specific Overdrive-capable device, a reset pulse at Overdrive speed has
to be issued followed by a Match ROM or Search ROM command sequence. This will shorten 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 will occur on the bus as
multiple slaves transmit simultaneously (open drain pulldowns will produce a wire-AND result).
Overdrive Match ROM [69H}
The Overdrive Match ROM command, followed by a 64-bit ROM sequence transmitted at Overdrive
Speed, allows the bus master to address a specific DS2506 on a multidrop bus and to simultaneously set it
in Overdrive Mode. Only the DS2506 that exactly matches the 64-bit ROM sequence will respond to the
subsequent memory function command. Slaves already in Overdrive mode from a previous Overdrive
Skip or Match command will remain in Overdrive mode. All other slaves that do not match the 64-bit
ROM sequence or do not support Overdrive will return to or remain at regular speed and wait for a reset
pulse of minimum 480 µs duration. The Overdrive Match ROM command can be used with a single or
multiple devices on the bus.
1-Wire Signalling
The DS2506 requires strict protocols to insure data integrity. The protocol consists of five types of
signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, Read Data
and Program Pulse. All these signals except presence pulse are initiated by the bus master. The DS2506
can communicate at two different speeds, regular speed and Overdrive Speed. If not explicitly set into the
Overdrive Mode, the DS2506 will communicate at regular speed. While in Overdrive Mode the fast
timing applies to all communication-related wave forms.
The initialization sequence required to begin any communication with the DS2506 is shown in Figure 9.
A Reset Pulse followed by a Presence Pulse indicates the DS2506 is ready to accept a ROM command.
The bus master transmits (TX) a reset pulse (tRSTL, minimum 480 µs at regular speed, 48 µs at Overdrive
Speed). The bus master then releases the line and goes into receive mode (RX). The 1-Wire bus is pulled
to a high state via the pullup resistor. After detecting the rising edge on the data pin, the DS2506 waits
(tPDH, 15-60 µs at regular speed, 2-6 µs at overdrive speed) and then transmits the presence pulse (tPDL,
60-240 µs at regular speed, 8-24 µs at Overdrive Speed).
A Reset Pulse of 480 µs or longer will exit the Overdrive Mode returning the device to regular speed. If
the DS2506 is in Overdrive Mode and the Reset Pulse is no longer than 80 µs the device will remain in
Overdrive Mode.
Read/Write Time Slots
The definitions of write and read time slots are illustrated in Figure 10. All time slots are initiated by the
master driving the data line low. The falling edge of the data line synchronizes the DS2506 to the master
by triggering a delay circuit in the DS2506. During write time slots, the delay circuit determines when the
DS2506 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay circuit
19 of 25
DS2506
determines how long the DS2506 will hold the data line low overriding the 1 generated by the master. If
the data bit is a “1”, the device will leave the read data time slot unchanged.
PROGRAM PULSE
To copy data from the 8-bit scratchpad to the EPROM Data or Status Memory, a program pulse of
12 volts is applied to the data line after the bus master has confirmed that the CRC for the current byte is
correct. During programming, the bus master controls the transition from a state where the data line is
idling high via the pullup resistor to a state where the data line is actively driven to a programming
voltage of 12 volts providing a minimum of 10 mA of current to the DS2506. This programming voltage
(Figure 11) should be applied for 480 µs, after which the bus master returns the data line to an idle high
state controlled by the pullup resistor. Note that due to the high voltage programming requirements for
any 1-Wire EPROM device, it is not possible to multi-drop non-EPROM based 1-Wire devices with the
DS2506 during programming. An internal diode within the non-EPROM based 1-Wire devices will
attempt to clamp the data line at approximately 8 volts and could potentially damage these devices.
INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 9
* In order not to mask interrupt signalling by other devices on the 1-Wire bus, tRSTL + tR should always be
less than 960 µs.
READ/WRITE TIMING DIAGRAM Figure 10
Write-one Time Slot
20 of 25
DS2506
READ/WRITE TIMING DIAGRAM Figure 10 (cont’d)
Write-zero Time Slot
Read-data Time Slot
NOTE:
For read-data time slots the optimal sampling point for the master is as close as possible to the end time
of the tRDV period without exceeding 15 µs for regular speed or 2 µs for overdrive speed. For the case of
a read-one time slot, this maximizes the amount of time for the pull-up resistor to recover the line to a
high level. For a read-zero time slot it ensures that a read will occur before the fastest 1-Wire device
releases the line (tRELEASE = 0).
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DS2506
PROGRAM PULSE TIMING DIAGRAM Figure 11
CRC GENERATION
With the DS2506 there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is a 8-bit
type and is stored in the most significant byte of the 64-bit ROM. The bus master can compute a CRC
value from the first 56 bits of the 64-bit ROM and compare it to the value stored within the DS2506 to
determine if the ROM data has been received error-free by the bus master. The equivalent polynomial
function of this CRC is: X8 + X5 + X4 + 1. This 8-bit CRC is received in the true (non-inverted) form
when reading the ROM of the DS2506. It is computed once at the factory and lasered into the ROM.
The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function X16
+ X15 + X2 + 1. This CRC is used to safeguard user-defined EPROM data when reading data memory or
status memory. It is the same type of CRC as is used with NV RAM based iButtons to safeguard data
packets of the iButton File Structure. In contrast to the 8-bit CRC, the 16-bit CRC is always returned in
the complemented (inverted) form. A CRC-generator inside the DS2506 chip (Figure 12) will calculate a
new 16-bit CRC at every situation shown in the command flow chart of Figure 5.
The DS2506 provides this CRC-value to the bus master to validate the transfer of command, address, and
data to and from the bus master. When reading the data memory of the DS2506 with the Read Memory
command, the 16-bit CRC is only transmitted as the end of the memory is reached. This CRC is
generated by clearing the CRC generator, shifting in the command, low address, high address and every
data byte starting at the first addressed memory location and continuing until the end of the implemented
data memory is reached.
When reading the status memory with the Read Status command, the 16-bit CRC is transmitted when the
end of each 8 byte page of the status memory is reached. At the initial pass through the Read Status flow
chart the 16-bit CRC will be generated by clearing the CRC generator, shifting in the command byte, low
address, high address and the data bytes beginning at the first addressed memory location and continuing
until the last byte of the addressed EPROM Status data page is reached. Subsequent passes through the
Read Status flow chart will generate a 16-bit CRC that is the result of clearing the CRC generator and
then shifting in the new data bytes starting at the first byte of the next page of the EPROM Status data
field and continuing until the last byte of the page is reached.
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DS2506
When reading the data memory of the DS2506 with the Extended Read Memory command, there are two
situations where a 16-bit CRC is transmitted. One 16-bit CRC follows each Redirection Byte, another
16-bit CRC is received after the last byte of a memory data page is read. The CRC at the end of the
memory page is always the result of clearing the CRC generator and shifting in the data bytes beginning
at the first addressed memory location of the EPROM data page until the last byte of this page. With the
initial pass through the Extended Read Memory flow chart the 16-bit CRC value is the result of shifting
the command byte into the cleared CRC generator, followed by the two address bytes and the Redirection
Byte. Subsequent passes through the Extended Read Memory flow chart will generate a 16-bit CRC that
is the result of clearing the CRC generator and then shifting in the Redirection Byte only.
When writing to the DS2506 (either data memory or status memory), the bus master receives a 16-bit
CRC to verify the correctness of the data transfer before applying the programming pulse. With the initial
pass through the Write Memory/Status flow chart the 16-bit CRC will be generated by clearing the CRC
generator, shifting in the command, address low, address high and the data byte. Subsequent passes
through the Write Memory/Status flow chart due to the DS2506 automatically incrementing its address
counter will generate an 16-bit CRC that is the result of loading (not shifting) the new (incremented)
address into the CRC generator and then shifting in the new data byte.
The comparison of CRC values and decision to continue with an operation are determined entirely by the
bus master. There is no circuitry on the DS2506 that prevents a command sequence from proceeding if
the CRC stored in or calculated by the DS2506 does not match the value generated by the bus master. For
more details on generating CRC values including example implementations in both hardware and
software, see the Book of DS19xx iButton Standards.
CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL Figure 12
23 of 25
DS2506
ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
*
-0.5V to +12.0V
-40°C to +85°C
-55°C to +125°C
See J-STD-020A specification
This is a stress rating only and functional operation of the device at these or any other conditions
outside those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Logic 1
Logic 0
Output Logic Low @ 4 mA
Output Logic High
Input Load Current
Operating Charge
Programming Voltage @ 10 mA
SYMBOL
VIH
VIL
VOL
VOH
IL
QOP
VPP
(VPUP=2.8V to 6.0V; -40°C to +85°C)
MIN
2.2
-0.3
TYP
VPUP
5
MAX
+0.8
0.4
6.0
30
12.0
11.5
CAPACITANCE
PARAMETER
Data (1-Wire)
NOTES
1, 6
1, 10
1
1, 2
3
7, 8
11
(TA = 25°C)
SYMBOL
CIN/OUT
MIN
AC ELECTRICAL CHARACTERISTICS
PARAMETER
Time Slot
Write 1 Low Time
Write 0 Low Time
Read Data Valid
Release Time
Read Data Setup
Recovery Time
Reset Time High
Reset Time Low
Presence Detect High
Presence Detect Low
Delay to Program
Delay to Verify
Program Pulse Width
Program Voltage Rise Time
Program Voltage Fall Time
UNITS
V
V
V
V
µA
nC
V
SYMBOL
tSLOT
tLOW1
tLOW0
tRDV
tRELEASE
tSU
tREC
tRSTH
tRSTL
tPDHIGH
tPDLOW
tDP
tDV
tPP
tRP
tFP
TYP
MAX
800
UNITS
pF
NOTES
9
(VPUP=2.8V to 6.0V; -40°C to +85°C)
MIN
60
1
60
0
1
480
480
15
60
5
5
480
0.5
0.5
24 of 25
TYP
15
15
MAX
120
15
120
45
1
60
240
5.0
5.0
UNITS
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
NOTES
12
5
4
11
11
11
DS2506
AC ELECTRICAL CHARACTERISTICS OVERDRIVE SPEED
(VPUP=2.8V to 6.0V; -40°C to 70°C)
PARAMETER
Time Slot
Write 1 Low Time
Write 0 Low Time
Read Data Valid
Release Time
Read Data Setup
Recovery Time
Reset Time High
Reset Time Low
Presence Detect High
Presence Detect Low
SYMBOL
tSLOT
tLOW1
tLOW0
tRDV
tRELEASE
tSU
tREC
tRSTH
tRSTL
tPDHIGH
tPDLOW
MIN
6
1
6
0
1
48
48
2
8
TYP
2
1.5
MAX
16
2
16
4
1
80
6
24
UNITS
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
NOTES
12
5
4
NOTES:
1. All voltages are referenced to ground.
2. VPUP= external pullup voltage.
3. Input load is to ground.
4. An additional reset or communication sequence cannot begin until the reset high time has expired.
5. Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data is
guaranteed to be valid within 1 µs of this falling edge.
6. VIH is a function of the external pullup resistor and VPUP.
7. 30 nanocoulombs per 72 time slots @ 5.0V.
8. At VCC=5.0V with a 5 kΩ pullup to VCC and a maximum time slot of 120 µs.
9. Capacitance on the data pin could be 800 pF when power is first applied. If a 5 kΩ resistor is used to
pullup the data line to VCC, 5 µs after power has been applied the parasite capacitance will not affect
normal communications.
10. Under certain low voltage conditions VILMAX may have to be reduced to as much as 0.5V to always
guarantee a presence pulse.
11. Operational temperature range for memory programming is -40°C to +50°C.
12. For read-data time slots the optimal sampling point for the master is as close as possible to the end
time of the tRDV period without exceeding 15 µs for regular speed or 2 µs for overdrive speed. For the
case of a read-one time slot, this maximizes the amount of time for the pull-up resistor to recover the
line to a high level. For a read-zero time slot it ensures that a read will occur before the fastest 1-Wire
device releases the line (tRELEASE = 0).
25 of 25