Delta RMC151 - Manual (Page 433)

6 Communication
• Most-Significant Byte (MSB) First (01). For
example, the value 0x1122 will be encoded as 11
22.
8-9 nn nn Starting Address (File). Gives the file number (f)
for the address (%MDf.e) to start the read at. The
order of the bytes in this 16-bit value is determined
by the Byte Order field.
10-11 nn nn Starting Address (Element). Gives the element
number (e) for the address (%MDf.e) to start the
read at. The order of the bytes in this 16-bit value is
determined by the Byte Order field.
12-13 nn nn Read Count. The number of 32-bit registers to read.
This value must be between 0 and 1024. The order of
the bytes in this 16-bit value is determined by the
Byte Order field.
The RMC will respond to this request with the following packet:
Offset Data
(hex)
Description
0-1 nn nn Packet Length. Indicates the total length in bytes of
this packet, excluding this 2-byte field. This 16-bit
value is encoded with the least significant byte first.
2-3 00 02 Static Values. These bytes will always have these
values in the response.
4-5 nn nn Transaction ID. This value will echo the Transaction
ID in the request. It can be used to match this
response to the corresponding request.
6 94 -or- 54 Function Code (Response). If the read was
processed successfully, this byte will be 94, otherwise
it will hold 54.
7 nn Response Code. Indicates whether the read was
successful or not. See the DMCP Response Codes
section below.
8-… … Data. The values of each register that was read will
follow the above header. Each 32-bit value is encoded
in either LSB- or MSB-first byte order, as determined
by the Byte Order field. For LSB-first byte order, the
value 16#11223344 will be encoded as 44 33 22 11.
For MSB-first byte order, this will be encoded as 11
22 33 44.
Register Addresses
This protocol uses the RMC’s two-level file/element addressing format. The IEC Addressing
topic describes how this addressing format works.
DMCP Response Codes
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.
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