Parker EME
RS232 & RS485 – interface record
I11 T11 192-120101 N6 - March 2004 79
5.2 Binary record
The binary record with block securing is based on 5 different telegrams:
! 2 request telegrams which the control sends to Compax3 and
! 3 response telegrams which Compax3 returns to the control.
Telegram layout
Basic structure:
Start code Address Number of data bytes - 1 Data block securing
SZ O L D0 D1 ... Dn Crc(Hi) Crc(Lo)
The start code defines the frame type and is composed as follows:
Bit 7 6 5 4 3 2 1 0
Frame type Frame identification PLC Gateway Address
RdObj Read object 1 0 1 0 x 1 x x
WrObj Write object 1 1 0 0 x 1 x x
RspAnswer 0000010 1
Ack Positive command acknowledgement 0 0 0 0 0 1 1 0
Nak Negative command acknowledgement 0 0 0 0 0 1 1 1
Bits 7, 6, 5 and 4 of the start code form the telegram identification; Bit 2 is always
“1“.
Bits 3, 1 and 0 have different meanings for the request and response telegrams.
The address is only necessary for RS484.
-> Compax3
! the address bit (Bit 0 = 1 ) shows if the start code is followed by an address (only
for RS485; for RS232 Bit 0 = 0)
! the gateway bit (Bit 1 = 1) shows if the message is to be passed on.
(Please set Bit 1 = 0, as this function is not yet available)
! the PLC bit (Bit 3 = 0 ) allows access to objects in the PLC format (U16, U32,
IEEE Floating Point). For information into which PLC format the objects are
converted, please refer to the object description.
Compax3 ->
! Bits 0 and 1 are used to identify the response
! Bit 3 is always 0
The maximum number of data bytes in the request telegram is 256, in the response
telegram 253.
The block securing (CRC16) is made via the CCITT table algorith for all characters.
After receiving the start code, the timeout monitoring is activated in order to avoid
that Compax3 waits in vain for further codes (e.g. connection interrupted) The
timeout period between 2 codes received is fixed to 5ms (5 times the code time at
9600Baud)
Request telegrams
Response telegram
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