Instruction Manual
N 143
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3. Interface
3.1. Interface data
Type: RS485
Baud rate: 19200
Parity: No
Data bits: 8
Stop bits: 1
Handshake: Nein
Redundancy check Yes (CRC)
Timeout reply*: 0,1...60 ms
* To avoid bus collisions, a minimum timeout reply of 1 ms (default parame-
ter) is to be kept, i.e. the time elapsed between transmission of the last bit
in the request until start of transmission of the first bit in the SPA’s re-
sponse.
The operator should see that due to the minimized timeout reply of 1 ms
the bus switching time after having transmitted the last bit must not exceed
1 ms.
Default parameters enable optional alteration by serial interface in incre-
ments of 0,1 ms within the range of 0,1...60 ms. Refer also to command „x“
(78h).
BUS switching time** <0,1 ms ** The BUS switching time is the time required by the SPA to be ready again
for transmission after having replied to the host.
3.2. Protocol
The spindle position display operates on ASCII protocol (clear text protocol). Depending on the command, the
protocol data package varies between 5 and 17 bytes.
Byte Hex-Code Significance Parameters
1 01H SOH = start of header ever 01h
2 XXh Adr = address 00...31dez + 20h Offset (address 00 = 20h)
3 XXh Cmd = command specific commands
4-n [XXh..XXh] [Data] = data 20h-7Fh
n+1 04h EOT = end of transmission ever 04h
n+2 XXh CRC = cyclic redundancy check 00h...FFh
3.3. Redundancy check (CRC byte)
For optimized error-free data communication the CRC byte is added after the footer (EOT, end of transmission)
to the string to be transmitted. Upon receiving a command the attached CRC byte 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 indicator (04H) to the string to be transmitted.
Note:
1101 0000 RL 1010 0001 Important: Bit 7 is shifted in bit 0 during rotation
Example:
String w/o CRC byte = 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