Dallas DS2505T 16-kbit add-only memory Datasheet

DS2505
16-kbit Add-Only Memory
www.dalsemi.com
PIN ASSIGNMENT
TO-92
DALLAS
DS2505
TSOC PACKAGE
GND
DATA
NC
1
2
3
6
5
4
NC
NC
NC
Top View
3.7 X 4.0 X 1.5 mm
Side View
See Mech.
Drawing Section
NC
16384 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 1-Wire
Net
products
EPROM partitioned into sixty-four 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
8-bit family code specifies DS2505
communications requirements to reader
Presence detector acknowledges when the
reader first applies voltage
Low cost TO-92 or 6-pin TSOC 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
DATA
GND
FEATURES
1 2 3
Bottom View
See Mech.
Drawings Section
ORDERING INFORMATION
DS2505
TO-92 Package
DS2505P
6-pin TSOC Package
DS2505/T&R Tape & Reel version of DS2505
DS2505P/T&R Tape & Reel version of DS2505P
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032201
DS2505
SILICON LABEL DESCRIPTION
The DS2505 16-kbit 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 DS2505 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 (0BH) plus
16 kbits of user-programmable EPROM. The power to program and read the DS2505 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 standalone
database. The 48-bit serial number that is factory-lasered into each DS2505 provides a guaranteedunique identity which allows for absolute traceability. The TO-92 and TSOC 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 DS2505. The DS2505 has three main data components: 1) 64-bit lasered ROM, 2) 16384-bits
EPROM Data Memory, and 3) 704 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 DS2505 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 four ROM Function Commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM.
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 DS2505 become accessible and the bus master may issue any one of the
five Memory Function Commands specific to the DS2505 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 DS2505 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 DS2505 to operate as a 1-Wire device and
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 DS2505 are not accessible until the ROM function
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DS2505
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 four ROM function commands: 1) Read ROM, 2) Match
ROM, 3) Search ROM, or 4) Skip 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
DS2505 (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 0. Then
starting with the least significant bit of the family code, one 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.
DS2505 BLOCK DIAGRAM Figure 1
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DS2505
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 (0BH)
LSB MSB
LSB
16384-BITS EPROM
The memory map in Figure 4 shows the 16384-bit EPROM section of the DS2505 which is configured as
64 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 a 16-bit
CRC from the DS2505 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 ensures data integrity when programming the memory. The details for
reading and programming the 16384-bit EPROM portion of the DS2505 are given in the Memory
Function Commands section.
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DS2505
EPROM STATUS BYTES
In addition to the 16384 bits of data memory the DS2505 provides 704 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 DS2505. The first 8 bytes of the EPROM Status Memory (addresses 000 to 007H)
contain the Write Protect Page bits which inhibit programming of the corresponding page in the 16384-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.
The next 8 bytes of the EPROM Status Memory (addresses 020 to 027H) contain the Write Protect bits
which inhibit altering the Page Address Redirection Byte corresponding to each page in the 16384-bit
main memory area.
The following 8 bytes within the EPROM Status Memory (addresses 040 to 047H) 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 DS2505.
The next 64 bytes of the EPROM Status Memory (addresses 100H to 13FH) contain the Page Address
Redirection Bytes which indicate if one or more of the pages of data in the 16384-bit EPROM section
have been invalidated by software and redirected to the page address contained in the appropriate
redirection byte. The hardware of the DS2505 makes no decisions based on the contents of the Page
Address Redirection Bytes. These additional bytes of Status EPROM allow for the redirection of an
entire page to another page address, indicating that the data in the original page is no longer considered
relevant or valid. With EPROM technology, bits within a page can be changed from a logical 1 to a
logical 0 by programming, but cannot be changed back. Therefore, 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 DS2505 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, the data in the page
corresponding to that redirection byte is invalid, and 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 details for reading and programming the EPROM status memory
portion of the DS2505 are given in the Memory Function Commands section.
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DS2505
The Status Memory address range of the DS2505 extends from 000 to 13FH. The memory locations
008H to 01FH, 028H to 03FH, 048H to 0FFH and 140H to 7FFH are physically not implemented.
Reading these locations will usually result in FFH bytes. Attempts to write to these locations will be
ignored. If the bus master sends a starting address higher than 7FFH, the five most significant address
bits are set to 0s by the internal circuitry of the chip. This will result in a mismatch between the CRC
calculated by the DS2505 and the CRC calculated by the bus master, indicating an error condition.
DS2505 MEMORY MAP Figure 4
STATUS MEMORY MAP
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DS2505
MEMORY FUNCTION COMMANDS
The “Memory Function Flow Chart” (Figure 5) describes the protocols necessary for accessing the
various data fields within the DS2505. 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 3-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 DS2505 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 16384-bit EPROM data field. The bus master
follows the command byte with a 2-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 DS2505 starting at the initial address and continuing until the end of the 16384-bit 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 DS2505 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 2 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 ensure 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 1-Wire 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 2-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 DS2505 starting at the supplied address and continuing until the end of an 8-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 DS2505 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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DS2505
MEMORY FUNCTION FLOW CHART Figure 5
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DS2505
MEMORY FUNCTION FLOW CHART Figure 5 (cont’d)
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DS2505
MEMORY FUNCTION FLOW CHART Figure 5 (cont’d)
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DS2505
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 2 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. After the 16-bit CRC of the last EPROM Status
data page is read, the bus master will receive logical 1s from the DS2505 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 16384-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 DS2505 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 DS2505.
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 DS2505 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 16384-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 2-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 16 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 DS2505 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 DS2505 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 16 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.
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DS2505
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 16,384-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.
The CRC received by the bus master directly following the Redirection Byte, is calculated in two
different ways. 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
2 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.
After the 16-bit CRC of the last page is read, the bus master will receive logical 1s from the DS2505 until
a Reset Pulse is issued. The Extended Read Memory command sequence can be exited at any point by
issuing a Reset Pulse.
WRITE MEMORY [0FH]/SPEED WRITE MEMORY [F3]
The Write Memory command is used to program the 16384-bit EPROM data field. The bus master will
follow the command byte with a 2-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
DS2505 and read back by the bus master to confirm that the correct command word, starting address, and
data byte were received.
The highest starting address within the DS2505 is 07FFH. If the bus master sends a starting address
higher than this, the 5 most significant address bits are set to 0 by the internal circuitry of the chip. This
will result in a mismatch between the CRC calculated by the DS2505 and the CRC calculated by the bus
master, indicating an error condition.
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 unprogrammed
16384-bit EPROM data 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 16384-bit EPROM will be
programmed to a logical 0 after the programming pulse has been applied at that byte location.
After the 480 µs programming pulse is applied and the data line returns to the idle level, the bus master
issues eight read time slots to verify that the appropriate bits have been programmed. The DS2505
responds with the data from the selected EPROM address sent least significant bit first. This byte
contains the logical AND of all bytes written to this EPROM data address. If the EPROM data 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 DS2505 EPROM data byte
contains 0s in the same bit positions as the data byte, the programming was successful and the DS2505
will automatically increment its address counter to select the next byte in the 16384-bit EPROM data
field. The new 2-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.
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DS2505
As the DS2505 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
DS2505 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 Memory
command 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 Memory flow chart will generate a 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 Memory flow chart due to the DS2505
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 DS2505) is made
entirely by the bus master, since the DS2505 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 DS2505. If an incorrect CRC is ignored and
a program pulse is applied by the bus master, incorrect programming could occur within the DS2505.
Also note that the DS2505 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 Memory command, incorrect programming could occur
within the DS2505. The Write Memory command sequence can be ended at any point by issuing a reset
pulse.
To save time when writing more than 1 consecutive byte of the DS2505’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. This saves 16 time slots or 976 µs for every byte to be programmed. This speedprogramming 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
DS2505 is firm, since a poor contact may result in corrupted data inside the EPROM memory.
WRITE STATUS [55H]/SPEED WRITE STATUS [F5]
The Write Status command is used to program the EPROM Status data field. The bus master will follow
the command byte with a 2-byte starting address (TA1=(T7:T0), TA2=(T15:T8)) and a byte of status data
(D7:D0). A 16-bit CRC of the command byte, address bytes, and data byte is computed by the DS2505
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 EPROM Status data 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 Status data field will be programmed to a logical
0 after the programming pulse has been applied at that byte location.
After the 480 µs programming pulse is applied and the data line returns to the idle level, the bus master
issues eight read time slots to verify that the appropriate bits have been programmed. The DS2505
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DS2505
responds with the data from the selected EPROM Status address sent least significant bit first. This byte
contains the logical AND of all bytes written to this EPROM Status Byte address. If the EPROM Status
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 DS2505 EPROM Status byte
contains 0s in the same bit positions as the data byte, the programming was successful and the DS2505
will automatically increment its address counter to select the next byte in the EPROM Status data field.
The new 2-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 DS2505 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
DS2505 with 16 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 Status command
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 Status flow chart will generate a 16-bit CRC value that is the
result of shifting the command byte into the CRC generator, followed by the 2 address bytes, and finally
the data byte. Subsequent passes through the Write Status flow chart due to the DS2505 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 DS2505) is made
entirely by the bus master, since the DS2505 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 DS2505. If an incorrect CRC is ignored and
a program pulse is applied by the bus master, incorrect programming could occur within the DS2505.
Also note that the DS2505 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 Status command, incorrect programming could occur
within the DS2505. The Write Status command sequence can be ended at any point by issuing a Reset
Pulse.
To save time when writing more than 1 consecutive byte of the DS2505’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. This saves 16 time slots or 976 µs for every byte to be programmed. This speedprogramming 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
DS2505 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
DS2505 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 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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DS2505
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 DS2505 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 bidirectional 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. The 1-Wire bus has a maximum
data rate of 16.3 kbits per second. If the bus master is also required to perform programming of the
EPROM portions of the DS2505, 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 120 µs, one or more of the devices on the bus may be
reset.
Transaction Sequence
The sequence for accessing the DS2505 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 DS2505 is on the bus and is ready to operate. For
more details, see the “1-Wire Signaling” section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the four ROM function commands. All
ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in
Figure 8):
Read ROM [33H]
This command allows the bus master to read the DS2505’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 DS2505 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).
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DS2505
DS2505 EQUIVALENT CIRCUIT Figure 6
BUS MASTER CIRCUIT Figure 7
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DS2505
ROM FUNCTIONS FLOW CHART Figure 8
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DS2505
Match ROM [55H]
The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a
specific DS2505 on a multidrop bus. Only the DS2505 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, three-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, three-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.
1-Wire Signaling
The DS2505 requires strict protocols to ensure 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
initialization sequence required to begin any communication with the DS2505 is shown in Figure 9. A
reset pulse followed by a presence pulse indicates the DS2505 is ready to accept a ROM command. The
bus master transmits (TX) a reset pulse (tRSTL, minimum 480 µs). 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 DS2505 waits (tPDH, 15-60 µs) and then transmits the
presence pulse (tPDL, 60-240 µs).
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 DS2505 to the master
by triggering a delay circuit in the DS2505. During write time slots, the delay circuit determines when
the DS2505 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay
circuit determines how long the DS2505 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 DS2505. This programming voltage
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DS2505
(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 multidrop non-EPROM based 1-Wire devices with the
DS2505 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 signaling by other devices on the 1-Wire bus, tRSTL + tR should always be
less than 960 µs.
READ/WRITE TIMING DIAGRAM Figure 10
RESISTOR
MASTER
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DS2505
READ/WRITE TIMING DIAGRAM Figure 10 (cont’d)
NOTE:
For read-data time slots the optimal sampling point for the master is as close as possible to the end of the
tRDV period without exceeding the 15 µs window. 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 land. 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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DS2505
PROGRAM PULSE TIMING DIAGRAM Figure 11
CRC GENERATION
With the DS2505 there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is an
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 DS2505
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 DS2505. 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 DS2505 chip (Figure 12) will calculate a
new 16-bit CRC at every situation shown in the command flow chart of Figure 5.
The DS2505 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 DS2505 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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DS2505
When reading the data memory of the DS2505 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 2 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 DS2505 (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 DS2505 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 DS2505 that prevents a command sequence from proceeding if
the CRC stored in or calculated by the DS2505 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
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DS2505
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
tPDH
tPDL
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
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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
DS2505
NOTES:
1. All voltages are referenced to ground.
2. VPUP = external pullup voltage. If VPUP is lower than 3.0V the first byte read (any read command)
may not reproduce the correct memory contents. Therefore, under low voltage conditions, it is
recommended to set either the most significant bit or all five most significant bits of TA2 to 1.
Internal circuitry of the chip will force these 5 bits back to 0 before they are shifted in the address
counter and CRC generator.
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 and will remain valid for 14 µs minimum.
(15 µs total from falling edge on 1-Wire bus.)
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
pull up 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 of
the tRDV period without exceeding the 15 µs window. 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 land. For a readzero time slot it ensures that a read will occur before the fastest 1-Wire device releases the line
(tRELEASE = 0)
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