Azbil C1M - Fixed-Length Continuous Data Read Command (RD Command)

7-9
Chapter 7. CPL Communication Function

Fixed-length continuous data read command (RD command)
This command reads continuous data in two-byte units. This command is suitable
for handling data in ladder programs sent by PLC communications as the data is of
a fixed length.
The starting word address is expressed as four hexadecimal digits. The data count
is expressed as four digits, and data is expressed as four × n (n is a positive integer)
hexadecimal digits.
z
Instruction message
The read starting word address (four hexadecimal digits) and the read data count
(four hexadecimal digits) are sent.
R D
(1) (2) (3)
(1) Fixed-length continuous data read
command
(2) Starting word address
(3) Read data count
z
Response message
If the command is processed successfully, a termination code indicating success
(two decimal digits) is returned with the specified number of read data records
(four hexadecimal digits × read data count). If there was an error, a termination
code indicating error (two decimal digits) is returned without appending the data
that was read.
• Normal termination (reading of single data record)
0 0
(1) (2)
• Normal termination (reading of multiple data records)
0 0
(1) (2) (3) (4)
• Abnormal termination
X X
A termination code indicating an error is entered in place of XX.
7 - 6 List of Termination Codes (p.7-15) (for details about termination
codes)
(1)
(1) Termination code
(2) Read data 1
(3) Read data 2 to (n−1)
(4) Read data n
z
Maximum read data count per message
64 words