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2.6. CRC are the last 2 bytes of a control block or a response block. They are
transmitted the lower byte ahead. All the block's bytes are convolved (except the
CRC bytes) for the calculation of the CRC. The block is supposed to be received error
free when the convolution of the received block's bytes together with the received
CRC bytes results in the value 0000h.
The initial convolution value is set to be equal FFFFh.
The polynomial for the CRC Calculation and the examples of the convolution have
been described in “Application Note 27. Understanding and Using Cyclic Redundancy
Checks with Dallas Semiconductor iButtonTM Products (www.dalsemi.com)”, in the
chapter “CRC-16 computation for ram records in iButtons” (see Mandatory Annex 3
for the current Protocol).
2.7. The location of all the bytes in the block is given in the Table 1: TypeR – the type
of the addressed (target) Device;
AddrR – the address of the target device;
TypeT – the type of the Device sending the current block; AddrT – the address of the
Device sending the current block; Ident – the 1st byte of the ID subblock;
IdentExt – the 2nd byte of the ID subblock;
Len – the length subblock (length of the following payload subblock measured with
bytes); Data 0 .. Data M – payload subblock, it has (M + 1) bytes in this example;
CRCL, CRCH – the lowest and the highest bytes of the CRC subblock.
Table 1. The sequence of the subblocks in a block
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 Byte 8 Byte 9 Byte 10
0E2h 0E4h TypeR AddrR TypeT AddrT Ident IdentExt Len Data 0
Byte N-2 Byte N-1 Byte N
Data M CRCL CRCH
3. DEVICE STATUS
The Device Status is transmitted in response to instructions of the Master and it has
the following format:
- Byte 1 — status of the process which is now active inside the device:
- bit 0 is set to "1" — the device is executing a process, the instruction of the pressed
button code cannot be executed at the moment;