Baumer N153 - Protocol; Checksum (Cyclic Redundancy Check); Data Transmission Properties; Broadcast Commands

N 153
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3.2. Protocol
The spindle position display operates with ASCII protocol (clear text protocol). Depending on the command, the
protocol data package varies between 5 and 17 bytes.
Byte Hex code Significance Values
1 01H SOH = start of heading permanent 01h
2 XXh Adr = identifier 00...31dez + 20h offset (identifier 00 = 20h)
3 XXh Cmd = command code specific commands
4-n [XXh..XXh] [Data] = data 20h-7Fh
n+1 04h EOT = end of transmission permanent 04h
n+2 XXh CRC = checksum 00h...FFh
3.3. Checksum (Cyclic Redundancy Check)
For optimized error-free data transmission the CRC byte is added after the footer token (EOT, end of transmis-
sion) to the string to be transmitted. Upon receiving a command the CRC byte transmitted is crosschecked with
the auto-calculated CRC byte.
Algorithm:
1) Reset CRC byte.
2) Rotate CRC byte by 1 bit to the left.
3) Link result to first data byte XOR.
4) Rotate result by 1 bit to the left.
5) Link result to the second data byte XOR.
:
x) Rotate result by 1 bit to the left.
y) Link result to the last data byte (ever 04H) XOR.
z) Add result as CRC after the footer token (04H) to the string transmitted.
Note:
1101 0000 RL 1010 0001 Important: Bit 7 is shifted in bit 0 during rotation
Example:
Transmitted string less CRC = 01h 20h 43h 04h
CRC-Byte = 0Ah
0000 0000 RL 0000 0000 XOR 0000 0001 (01h) = 0000 0001
0000 0001 RL 0000 0010 XOR 0010 0000 (20h) = 0010 0010
0010 0010 RL 0100 0100 XOR 0100 0011 (43h) = 0000 0111
0000 0111 RL 0000 1110 XOR 0000 0100 (04h) =
0000 1010
= CRC
Legend: RL = rotate left; XOR = antivalence link
3.4. Data transmission properties
For reasons of compatibility, within the complete multicon system the amount of data is always the same (see
table in chapter 6), no matter how many digits are in the display. For example, command “R” (read actual value)
comprises a transmitted data amount of 6 bytes, but only 5 digits are indicated in the display. If it is a negative
value, digit 6 respectively digit 5 is always 0 (30h).
3.5. Broadcast commands
Some specific commands are designated so-called broadcast commands. As soon as the master broadcasts a
command to identifier 99, the command is addressed to every multicon device in the network. Each individual
SPA will accomplish the respective command but will not respond any confirmation to master.