1 of 2 – Micromod Micro-DCI: 53MC5000 PLC AND PRINTER INTERFACES User Manual
Page 75
Table 6-5. Write Control Bytes for PCS Modbus Master
Title
Definition
DDI-A DDI-B
Set
By
De-
fault
PLC Address
It is the address of the PLC to be accessed. B674
B650
User
0
Starting PLC Memory
Address Low (or
Diagnostic Code Low)
The two byte PLC memory address that
states where to start writing data into the
PLC memory. Each byte is a decimal
number; however, both bytes together
function as a 16 bit unsigned binary integer
(see Table 6-4, Read Control Bytes for PCS
Modbus Master). For Diagnostic Command
information, see Section 6.4.13.
B675
B651
User
0
Starting PLC Memory
Address High (or
Diagnostic Code
High)
B676
B652
User
0
Number of L-Words
to Write (Diagnostic
Reply Data Low)
The number of L-words that are to be
written to the PLC. For Diagnostic
Command information, see Section 6.4.13.
B677
B653
User
0
Number of C-Words
to Write (Diagnostic
Reply Data High)
The number of C-words that are to be
written to the PLC. For Diagnostic
Command information, see Section 6.4.13.
B678
B654
User
0
Function Code
It is the write command function code as
follows:
6 = Preset Single Holding Register (C)
8 = Loopback Diagnostic (see Section
6.4.13)
15 = Force Multiple Coils (L)
16 = Preset Multiple Holding Registers
(PLC registers may contain L-values.)
B679
B655
User
0
PLC Error Code*
(Exception Response
Code)
Exception Response Codes 1-7 can be sent
from the PLC to the PCS master (see the
Modbus documentation for complete
definitions.)
01 - Illegal Function: Does not exist as a
valid function code.
02 - Illegal Data Address: Not an allowable
address.
03 - Illegal Data Value: The fetch quantity
requested is not allowed.
04 - Failure In Associated Device: The
slave failed to respond to the message.
05 - Acknowledge: The slave has accepted
and is processing a long duration
command.
06 - Busy, Rejected Message: The slave is
busy processing a long duration com-
mand.
07 - NAK, Negative Acknowledgement: The
program function just requested can not
be performed.
B681
B657
Soft-
ware
0
1 of 2
Section 6. MODBUS RTU Mode
MODBUS2
6-11