Delta RMC151 - Manual (Page 438)

RMC70/150 and RMCTools User Manual
The response packet holds a single-byte Response Code field, indicating to the client
whether the transaction was successful or not. Notice that the Response Function Code
byte will also indicate whether the Response Code is 00 (success) or not. If the Response
Code is 00, then the Response Function Code will match the request’s Function Code plus
0x80. Otherwise, the Response Function Code will match the request’s Function Code plus
0x40.
Response
Code
Description
00 Success.
01 Malformed.
02 Too Long.
03 Invalid Address.
Notice that in certain other error cases, the RMC will not generate a response to the
DMCP request. Such cases include the following:
• UDP datagram is less than 7 bytes in length.
• UDP datagram size does not match the Packet Length field. The UDP datagram length
must always be 2 bytes longer than the Packet Length field.
• The Static Values (bytes 2-3) are not 00 and 02 respectively.
• Unsupported Function Code.
Example 1: Writing a Single Register
In this example, the client will write the value 0x11223344 to variable 0 (%MD56.0),
using the LSB-first byte order (00). The client chooses a Transaction ID of 00 00 for this
packet, either because he is not using this field, or because this is the first transaction.
Plugging in the above values in the proper byte order gives us the following packet that
should be sent to UDP port 1324 on the RMC:
12 00 00 02 00 00 15 00
38 00 00 00 01 00 00 00
44 33 22 11
After the RMC has successfully received and processed this write request, it will respond
with the following packet:
06 00 00 02 00 00 95 00
Notice that the last byte is the Response Code, with 00 meaning success.
Example 2: Reading a Single Register
In this example, the client will read a value from variable 0 (%MD56.0). The client
chooses a Transaction ID of 0x0001, perhaps because this is the second transaction.
Plugging in the above values in the proper byte order gives us the following packet that
should be sent to UDP port 1324 on the RMC:
0C 00 00 02 01 00 14 00
38 00 00 00 01 00
After the RMC has successfully received and processed this write request, it will respond
with the following packet if variable 0 held the value 0x11223344:
0A 00 00 02 01 00 94 00
44 33 22 11
Notice that byte 7 holds the Response Code, and bytes 8-11 hold the data that was read.
418 Delta Computer Systems, Inc.