Nor-Cal SDC15 Controller - Manual (Page 166)

■ 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 start data address is expressed as four hexadecimal digits. The data count is
expressed as four digits, and data is expressed as four X n (n is a positive integer)
hexadecimal digits.
● Send message
The read start data address (four hexadecimal digits) and the read data count (four
hexadecimal digits) are sent.
● Response message
If the message is sent successfully, the termination code is taken to be normal (two
decimal digits) and returned appended with the read data count (four hexadecimal
digits X read data count) specified by the command. If message transmission ends
in error, the termination code is taken to be in error (two decimal digits) and
returned without the read data appended.
● Maximum read data count per message
Up to 28 words for both RAM and EEPROM areas
7-8
Chapter 7. CPL COMMUNICATIONS FUNCTIONS
(1) Fixed length continuous data read command
(2) Start data word address
(3) Data count
R
(1)
D
(2) (3)
0
• Normal termination (reading of single data item)
(1)
0
• Normal termination (reading of multiple data items)
0
(1)
0
(2) (3) (4)
• Abnormal termination
X
(1)
X The abnormal termination code is entered at XX.
For details of codes,
refer to
7-6, List of Termination Codes (on page 7-14).
(2)
(1) Termination code
(2) Data
(3) Data 2 to (n-1)
(4) Data (n)