DS1963S

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command, the master must provide the 2-byte target address. After these 2 bytes, the master reads data

beginning from the target address and may continue until the end of the PRNG counter and beyond. The

12 bytes following the PRNG counter are undefined. If the master continues reading the result will be

logic 1’s. It is important to realize that the target address registers will point to the last byte read. The

ending offset/data status byte is unaffected.

The hardware of the DS1963S provides a means to accomplish error-free writing to the memory section.

To safeguard reading data in the 1-Wire environment and to simultaneously speed up data transfers, it is

recommended to packetize data into data packets of the size of one memory page each. Such a packet

would typically store a master-calculated 16-bit CRC 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 Application Note 114 for the recommended file structure, which is also referred to as

TMEX Format.)

Erase Scratchpad [C3h]

The purpose of this command is to clear the HIDE flag and to wipe out data that might have been left in

the scratchpad from a previous operation. After having issued the command code the bus master transmits

a target address, as with the write scratchpad command, but no data. Next the whole scratchpad will be

automatically filled with FFh bytes, regardless of the target address. This process takes approximately 32

µs during which the master reads 1’s. After this the master reads a pattern of alternating 0’s and 1’s

indicating that the command has completed. The master must read at least 8 bits of this alternating

pattern. Otherwise the device might not properly respond to a subsequent Reset Pulse.

Match Scratchpad [3Ch]

SHA-1 MACs calculated by the DS1963S are written into the scratchpad. Some calculations such as

those done by the Authenticate Host or Validate Data Page function cause the HIDE flag to be set as well.

The Match Scratchpad command allows this data to be checked without making it publicly readable. The

command compares the 160-bit Message Authentication Code which is found in scratchpad locations

8 through 27 after a SHA computation, as described in the sections “SHA-1 Computation Algorithm” and

“SHA-1 Output Message Formats”, to the result that the master has computed by its own means. After the

master has issued the Match Scratchpad command code it transmits 1 byte after another starting with byte

8 and ending with byte 27. If all bytes match, the master will read a pattern of alternating 0’s and 1’s. If in

addition the AUTH-flag was set, the MATCH-flag will be set. If the comparison was not successful the

master will read all 1’s. The master must read at least 8 bits after having received the inverted CRC16.

Otherwise the device might not properly respond to a subsequent Reset Pulse.