Abstract: The 'family-code' embedded in the lasered ROM number of each 1-Wire device signifies a specific device type. Since each device type has different features and commands, it is imperative the 1-Wire master knows how to translate this 'family-code' into the correct commands. This document presents a method to dynamically configure the 1-Wire master to correctly communicate with a previously unknown 1-Wire device type by providing the 1-Wire master with an XML configuration file. This document was originally created to support the IEEE® 1451.4 A Smart Transducer Interface for Sensors and Actuators—Mixed-Mode Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats standards committee.
Introduction
The 'family-code' embedded in the lasered ROM number of each 1-Wire device signifies a specific device type. Since each device type has different features and commands, it is imperative the 1-Wire master knows how to translate this 'family-code' into the correct commands. Unfortunately, since the 'family-code' is only an 8-bit value it is impossible to encode all of the features and commands in it. Instead the 1-Wire master must make this association by different means. One method is to hardcode this association in the source code of the 1-Wire master. It can then be updated by rewriting the source code to accommodate new devices. This method is expensive and in some cases impossible thus relegating some 1-Wire masters to only deal with legacy devices.
This document presents a method to dynamically configure the 1-Wire master to correctly communicate with a previously unknown 1-Wire device type by providing the 1-Wire master with a configuration file. The 1-Wire master could be updated with the latest 1-Wire devices by providing a new configuration file. This document describes the format of one such configuration file utilizing XML. This document was originally created to support the IEEE 1451.4 A Smart Transducer Interface for Sensors and Actuators—Mixed-Mode Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats standards committee.
The appendix proposes a method where a generic family code (for example FD hex) could be differentiated by means of a read-only configuration memory page on the device. No devices currently implement this method.
Command Notation
It is assumed that each 1-Wire master must come with the ability to search for 1-Wire devices and read the unique ROM number associated with each device. From the ROM number the 8-bit 'family-code' can be extracted. The 1-Wire master will then perform 1-Wire operations as defined by this configuration file based on the 'family-code'. By examining all 1-Wire device operations, a minimum set of commands was derived. The commands are described in Table 1 along with a suggested notation. Table 2 describes additional commands that add verification to the
command sequences.
Table 1. Core 1-Wire Commands
Notation
Command Description
XX
Send the following hex byte value to the 1-Wire bus. If this hex byte is within a CRC block then calculate the CRC on the result of the 1-Wire operation (see verification commands).
{L, delay}
Delay for 'L' milliseconds
{M}
Select the device with a 1-Wire reset, Match ROM command, and device ROM
{P}
Prime 1-Wire power delievery (strong pull-up) or to occur after the next 1-Wire byte
{N}
Restore normal pull-up
{U}
Issued a 12-volt pulse (used in EPROM programming)
{Ax}
Supply a memory address where 'x' is a number 0,1,...representing the LSB to MSB. For example '{A0}{A1}' would specify a 16-bit address with the least significant byte first followed by the most significant byte.
{Dx}
Data to write to a memory device where the 'x' is a number 0,1,...representing the LSB to MSB of the data. For example '{D0} {D1} {D2}' is three bytes of data to write. Note the master processing these commands would place the actual data into the command flow.
{R}
Read memory bytes to end of memory. All values read are valid data however now verification is performed.
Table 2. Verification Commands
Notation
Command Description
{dx}
Data to read. This data can be for verification of data written to a memory 1-Wire device or result data such as a temperature conversion. Note it is in same format as the {Dx} command where 'x' is a number indicating the byte number with {d0} being the LSB.
{T}
Success is reading toggling bits such as 0xAA or 0x55.
{00}
Success is reading all 0's such as 0x00
{FF}
Success is reading all 1's such as 0xFF
{CRC16,start,seed}
Start CRC16 calculation by first setting the CRC16 to the provided 'seed' represented in hex notation. All following command bytes will be included in the calculation until the 'check' command is found.
{CRC16,check,value}
Check the CRC16 calculated value to make sure it equals the provided hex 'value'. If it is not then this is a failure. The CRC16 calculation can be stopped after the check.
{CRC8,start,seed}
Start CRC8 calculation by first setting the CRC8 to the provided 'seed' represented in hex notation. All following command bytes will be included in the calculation until the 'check' command is found.
{CRC16,check,value}
Check the CRC8 calculated value to make sure it equals the provided hex 'value'. If it is not then this is a failure. The CRC8 calculation can be stopped after the check.
See Figure 1 to see an example command sequence to read the scratchpad of the DS18B20.
Figure 1. DS18B20 read temperature command sequence and 1-Wire master translation.
Device Types
The general types of 1-Wire devices covered by this document are Memory, Switch, and Temperature.
The Memory device has some kind of data storage memory area. It may be write-once but must support multiple reads. It is often arranged in pages and is usually written a page at a time. A Memory device may have multiple banks of memory with different attributes.
The Switch device can control a latch. The latch may connect the output to ground (lowside) or to the communication channel (highside). Some Switch devices can also sense voltage. A Switch device can have multiple channels.
The Temperature device returns a temperature value in Celsius. The result is a signed value representing temperature units. The unit conversion to Celsius is provided.
Each device type contains one or more standard operations. For example each Temperature device has a 'read' operation. Table 3 shows the standard operations and attributes of each device type.
Table 3. Device Operations and Attributes by Type
Device Type
Operations
Attributes
Memory
Read
Write
Read/Write/ReadOnly/WriteOnce
Starting physical address
Number of pages
Page length in bytes
Min Temperature
Max Temperature
Step (unit of Celsius returned from Read)
The 'Setup' operation is also included in any of the device type descriptions. A 'Setup' is a command sequence that readies the device for operation. For any of the 'Read' operation there are also two attributes 'AndMask' and 'Polarity'. The 'AndMask' is a hex value that is bitwise anded with the result data described in the command sequence with {d0}. The 'Polarity' indicates that the operation is 'TRUE' if it matches the resulting value from the 'AndMask'. For example when reading the latch state (Read Latch) of a DS2406 channel A, the AndMask="0x01" and Polarity="0x00". So the value read from the command sequence is bitwise anded with 0x01 and if the result is 0, the latch is ON.
Configuration Format
The XML syntax was selected for the example configuration file format. Since XML is so 'eXtensible' it was easy to incorporate the device types, operations, attributes and the actual command sequences into a human readable format. The overall 'tag' for grouping these descriptions was <DeviceDescriptions>. Within this group are individual device descriptions with a specified family code attribute, for example: <Device FamilyCode="0x23">. Each device group can contain <MemoryBank>, <SwitchChannel>, or <TemperatureChannel> groups that correspond to the device types already described. Note that some devices may have more then one channel and group. For example the DS2406 has both memory and switch groups since it incorporates both of these features. See the Figure 2 in the appendix for an example XML file describing six different 1-Wire devices. Two of these devices are memory, two are switches, and two are temperature devices.
Figure 2. Example XML configuration file for six 1-Wire devices.
XML Device Description Schema
The device description schema provides a template to add support for new devices to their systems. The schema defines devices that support memory, switching, and temperature reading.
The following general memory description describes an idealized memory device with a configuration page that provides all of the necessary information to utilize the remaining memory space. The configuration page could provide the device type differentiation that is currently implemented with the ROM family code but with more information conveyed. A common generic family code (for example FD hex) could be used for all devices with this configuration page.
All 1-Wire memory devices support the Read Memory command (F0 hex), and with the exception of the DS2430A, it requires 2 address bytes. For this example the Read Memory command will be used to retrieve the configuration page information at a fixed address of FF7F hex. The memory location will have a length byte, 26 bytes of data followed by an inverted CRC16 for validation. Table A1 provides the bit-level details of the configuration page format.
Table A1. Configuration Page Format
Byte Offset
Name
Content
0
Length
Length of data in the configuration page (fixed at 26)
1
General_Flags
Bit 0
Memory type (1 EEPROM, 0 EEPROM)
Bit 1
Scratchpad erased on read-memory (1 YES, 0 NO)
Bit 2
Device has read page with CRC16 (1 YES, 0 NO)
Bit 3
Device has write-once mode like pseudo EPROM (1 YES, 0 NO) (EEPROM only)
Bit 4
Device has map of used pages (1 YES, 0 NO)
Bit 5
not used 0
Bit 6
not used 0
Bit 7
not used 0
2
WriteProt_Flags
Bit 0
Individual page write-protect (1 YES, 0 NO)
Bit 1
Global device write-protect (1 YES, 0 NO)
Bit 2
Write protect register is organized with one page per bit (1 YES, 0 NO). If not then one page per byte
Bit 3
not used 0
Bit 4
not used 0
Bit 5
not used 0
Bit 6
not used 0
Bit 7
not used 0
3
CRC_Flags
Bit 0
Write scratchpad has CRC16 (1 YES, 0 NO)
Bit 1
Read scratchpad has CRC16 (1 YES, 0 NO)
Bit 2
Read special memory command has CRC16 (1 YES, 0 NO)
Bit 3
not used 0
Bit 4
not used 0
Bit 5
not used 0
Bit 6
not used 0
Bit 7
not used 0
4
Scratchpad_Length
Length of scratchpad in bytes (EEPROM only)
5
Page_Length
Length of normal memory page in bytes
6
Pages
Number of pages (2 bytes)
8
Special_Pages
Number of special function pages
9
Special_Page_Length
Length of special memory page in bytes
10
ReadScratch_CMD
Read scratchpaf command
11
Write_CMD
Write command (scratchpad for EEPROM)
12
CopyScratch_CMD
Copy scratchpad command
13
ReadPageCRC_CMC
Read page of memory with CRC16 command
14
ReadSpecial_CMD
Read special memory page command
15
Write_Special_CMD
Write special memory command
16
WriteProt_Addr
Address of write-protect registers in special memory. (2 bytes)
18
WriteProtDev_Addr
Address of write-protect entire device register in special memory. (2 bytes)
20
WriteOnce_Addr
Address to write-once mode (pseudo EPROM) flag in special memory. (2 bytes)
22
UsedPgs_Addr
Address in special memory for map of used pages. (2 bytes)
24
UsedPgs_Offset
Bit offset of the map of used pages
25
WriteProt_Value
Value written to special memory register to write-protect a page.
26
WriteOnce_Value
Value written to special memory register to make a page write-once like pseudo EPROM.
27
CRC16
Bitwise inverted CRC16 of bytes 0 to 24, LSB first. (2 bytes)
The following table lists the operations that will be described by the configuration page.
Table A2. Operations
Operation
EEPROM
EPROM
Description
Read Memory
X
X
Read memory with device generated CRC
Read Page with CRC
x
x
Read a page of memory with device generated CRC
Write Scratchpad
X
Write the scratchpad in preparation of writing ot memory
Read Scratchpad
X
Read the scratchpad to verify the write was correct
Copy Scratchpad
X
Copy the scratchpad to the final memory location
Write Memory
X
Write a byte to memory
Read speical page with CRC
x
Read a page of special memory with device generated CRC
Write special byte
x
Write a byte to the special memory
Write protect page
x
x
Write protect a page
Set page for write-once
x
Set an EEPROM page to be write-once like (pseudo EPROM)
Calculate Free Pages
x
Calculate the number of free pages in an EPROM device by looking at the map of used pages.
X supported by all devices of this type
x supported by some devices of this type
<blank> generally not supported by devices of this type
Operations Detail
The operations detail listed in Table A2 can be implemented with the details provided by the configuration page. This section provides the sequence and data fields to use to implement the operations.
Read Memory
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write ReadMemory command (F0 hex)
Write first address byte TA1, LSB
Write second address byte TA2, MSB
Read data
Read Page with CRC
If General_Flags.Bit2 = 1
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write ReadPageCRC_CMD
Write first address byte TA1, LSB
Write second address byte TA2, MSB
Read Page_Length bytes (unless address is not at page beginning)
Read bitwise inverted CRC16
Write Scratchpad
If General_Flags.Bit0 = 1
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write Write_CMD
Write first address byte TA1, LSB
Write second address byte TA2, MSB
Write data bytes
If CRCFlags.Bit0 = 1 AND at end of page
Read bitwise inverted CRC16
Read Scratchpad
If General_Flags.Bit0 = 1
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write ReadScratch_CMD
Read first address byte TA1, LSB
Read second address byte TA2, MSB
Read offest and status flags ES
Read data bytes
If CRCFlags.Bit1 = 1 AND at end of page
Read bitwise inverted CRC16
Copy Scratchpad
If General_Flags.Bit0 = 1
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write CopyScratch_CMD
Write first address byte TA1, LSB
Write second address byte TA2, MSB
Write offset and status flags ES
Strong pullup applied to 1-Wire for a minimum of 10ms
Read confirmation byte (should be AA or 55)
Write Memory
If General_Flags.Bit0 = 0
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write Write_CMD
Write first address byte TA1, LSB
Write second address byte TA2, MSB
Write data byte to write
Read bitwise inverted CRC16 of command, address, and data (first pass) or address and data (second pass)
Apply 480µs 12V programming pulse on the 1-Wire
Read confirmation data byte (should OR of old data and current data bytes)
If next address to write is sequential then can send the next data byte...
Read Special Page with CRC
If General_Flags.Bit2 = 1
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write ReadSpecial_CMD
Read first address byte TA1, LSB
Read second address byte TA2, MSB
Read Special_Page_Length bytes (unless address is not at page beginning)
Read bitwise inverted CRC16
Write Special Byte
If General_Flags.Bit0 = 0
1-Wire reset and presence
ROM level command sequence (read/search/match/overdrive match/overdrive skip)
Write Write_Special_CMD
Write first address byte TA1, LSB
Write second address byte TA2, MSB
Write data byte to write
Read bitwise inverted CRC16 of command, address, and data (first pass) or address and data (second pass).
Apply 480µs 12V programming pulse on the 1-Wire
Read confirmation data byte (should OR of old data and current data bytes)
If next address to write is sequential then can send the next data byte...
Write Protect Page
If WriteProt_Flags.Bit0 = 1
If WriteProt_Flags.Bit2 = 1
Address = WriteProt_Addr + Page/8
Data = WriteProt_Value Rotate left Remainder (Page/8)
Data = BitInverse (1 Rotate left Remainder ((Page + UsedPgs_Offest)/8)
Write special byte at Address and Data
Calculate Free Pages
If General_Flags.Bit4 = 1
Address = UsedPgs_Addr
Read special page with CRC starting at Address until (Special_Pages/8) number of bytes read
Count the number of 1's in the bytes read, this is the number of free pages
Table A3 provides example configuration pages using existing devices as a template. Note however, these devices do not currently contain the configuration page.
Table A3. Example Configuration Pages
#
Name
Content
DS2433
DS2406
DS2505
DS2506
DS2431
DS28E04
0
Length
Length of data in the configuration page
1A
1A
1A
1A
1A
1A
1
General_Flags
Bit 0
Memory type (1 EEPROM, 0 EPROM)
1
0
0
0
1
1
Bit 1
Scratchpad erased on read-memory (1 YES, 0 NO)
1
0
0
0
1
1
Bit 2
Device has read page with CRC16 (1 YES, 0 NO)
0
1
1
1
1
1
Bit 3
Device has write-once mode like pseudo EPROM (1 YES, 0 NO) (EEPROM only)
0
0
0
0
1
1
Bit 4
Device has map of used pages (1 YES, 0 NO)
0
1
1
1
0
0
Bit 5
not used
0
0
0
0
0
0
Bit 6
not used
0
0
0
0
0
0
Bit 7
not used
0
0
0
0
0
0
2
WriteProt_Flags
Bit 0
Individual page write-protect (1 YES, 0 NO)
0
1
1
1
1
1
Bit 1
Global device write-protect (1 YES, 0 NO)
0
0
0
0
0
0
Bit 2
Write protect register is organized with one page per bit (1 YES, 0 NO). If no then is one page per byte.
0
1
1
1
0
0
Bit 3
not used
0
0
0
0
0
0
Bit 4
not used
0
0
0
0
0
0
Bit 5
not used
0
0
0
0
0
0
Bit 6
not used
0
0
0
0
0
0
Bit 7
not used
0
0
0
0
0
0
3
CRC_Flags
Bit 0
Write scratchpad has CRC16 (1 YES, 0 NO)
1
0
0
0
1
1
Bit 1
Read scratchpad has CRC16 (1 YES, 0 NO)
0
0
0
0
1
1
Bit 2
Read special memory command has CRC16 (1 YES, 0 NO)
0
1
1
1
0
0
Bit 3
not used
0
0
0
0
0
0
Bit 4
not used
0
0
0
0
0
0
Bit 5
not used
0
0
0
0
0
0
Bit 6
not used
0
0
0
0
0
0
Bit 7
not used
0
0
0
0
0
0
4
Scratchpad_Length
Length of scratchpad in bytes (EEPROM only)
20
00
00
00
08
20
5
Page_Length
Length of normal memory page in bytes
20
20
20
20
20
20
6
Pages
Number of pages
10 00
04 00
40 00
00 01
04 00
10 00
8
Special_Pages
Number of special function pages
00
01
0B
0B
01
02
9
Special_Page_Length
Length of special memory page in bytes
00
08
08
08
08
20
10
ReadScratch_CMD
Read scratchpad command
AA
00
00
00
AA
AA
11
Write_CMD
Write command (scratchpad for EEPROM)
0F
0F
0F
0F
0F
0F
12
CopyScratch_CMD
Copy scratchpad command
55
00
00
00
55
55
13
ReadPageCRC_CMD
Read page of memory with CRC16 command
00
A5
A5
A5
00
00
14
ReadSpecial_CMD
Read special memory page command
00
AA
AA
AA
F0
F0
15
Write_Special_CMD
Write special memory command
00
55
55
55
0F
0F
16
WriteProt_Addr
Address of write-protect registers in special memory. (2 bytes)
00 00
00 00
00 00
00 00
80 00
00 20
18
WriteProtDev_Addr
Address of write-protect entire device register in special memory. (2 bytes)
00 00
00 00
00 00
00 00
00 00
00 00
20
WriteOnce_Addr
Address to write-once mode (pseudo EPROM) flag in special memory. (2 bytes)
00 00
00 00
00 00
00 00
80 00
00 20
22
UsedPgs_Addr
Address in special memory for map of used pages. (2 bytes)
00 00
00 00
40 00
40 00
00 00
00 00
24
UsedPgs_Offset
Bit offset of the map of used pages
00
04
00
00
00
00
25
WriteProt_Value
Value written to special memory register to write-protect a page.
00
00
00
00
55
55
26
WriteOnce_Value
Value written to special memory register to make a page write-once like pseudo EPROM.
00
00
00
00
AA
AA
27
CRC16
Bitwise inverted CRC16 of bytes 0 to 24, LSB first. (2 bytes)
xx xx
xx xx
xx xx
xx xx
xx xx
xx xx
X single numbers are binary (0 or 1)
XX double numbers are in hex
The DS2506, DS2409, and DS2430A are no longer recommended for new designs.
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
IEEE is a registered service mark of the Institute of Electrical and Electronics Engineers, Inc.
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