Baumer N 141 - Manual (Page 5)

N 141
www.baumer.com 5
3. Interface
3.1. Interface data
Type: RS485
Baudrate: 19200
Parity: No
Data bits:
8
Stop bits: 1
Handshake: No
Redundancy check:
Yes (CRC)
* To avoid bus collisions a minimum timeout reply of 1 ms (default parameter)
is to kept, i.e. the time elapsed between transmitting the last bit of the
query until start transmitting the 1st bit of the SPA response.
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.
The default parameter of 1 ms can optionally be altered by serial interface
in steps of 0,1 ms within the range of 0,1 ... 60 ms.
Refer to command „x“ (78h).
Timeout reply*: 0,1...60 ms
BUS switching time**: <0,1 ms
** The BUS switching time is the time the SPA requires to be ready again for
reception after having replied to the host
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 Parameters
1 01H SOH = start of heading permanent 01h
2 XXh Adr = address/identifier 00 ... 31dez + 20h Offset (identifier 00 = 20h)
3 XXh Cmd = command code Defined commands
4-n [XXh..XXh] [Data] = data 20h-7Fh
n+1 04h EOT = end of transmission Permanent 04h
n+2 XXh CRC = redundancy check 00h ... FFh
3.3. Redundancy check (CRC byte)
For optimized error-free data transmission the CRC byte is added after the footer token (EOT, end of
transmission) to the string to be transferred. 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 transmitted string.
Note:
1101 0000 RL 1010 0001 Important: Bit 7 is shifted in bit 0 during rotation
Example:
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