4 DATA COMMUNICATION USING BIDIRECTIONAL PROTOCOL
4.1 Receiving Data from Target Device
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■Sum check code
The sum check code expresses the numeric value for the lower two bytes (16 bits) of the results (sum) from the addition of the
data length and the data portion in the message as binary code data.
When sum check code is enabled in the transmission setting of Engineering tool, it is necessary to add a sum check code at
the end of the message.
• Target device C24
C24 checks and processes the sum check code received. It cannot be read from the program.
When "None" is specified for "Sum check code", once data portion of message corresponding to the data length is
received, the succeeding data received will be ignored up to the control code that follows.
• C24 target device
C24 calculates and adds the sum check code to be transmitted.
When "None" is specified, no sum check code is transmitted.
Sum check code when "ABCDEFGHIJ " and the numeric value 100 are sent as data (when the unit is in bytes.)
■Error code
The error code indicates the definition of the error during NAK response.
For details on the error codes, refer to the following section.
Page 473 Error Code List
• Target device C24
For error codes from the target device, transmit the codes specified by the user.
The error codes (0022H to 005FH) that are not used by C24 can be used.
C24 stores the received error codes as a completion status in the control code for the BIDOUT instruction. They are also
stored in the 'data transmission result' (Un\G599).
• C24 target device
C24 adds an error code.
When an error code is transmitted, C24 writes the same error code in the 'data reception result' (Un\G600).
ABCDE FGH I J
LH L HL H
00 000000 11111100
03H 27H
b15 b8 b7 b1 b0
0CH 00H 41H 47H42H 43H 44H 45H 46H 48H 49H 4AH 64H 00H 27H 03H05H
C24
(L)(H)
(H)(L)
E
N
Q
0CH+00H+41H+42H+43H+44H+45H+46H+
47
H+48H+49H+4AH+64H+00H
100
(0064H)
Arbitrary data
Data
Data
length
(000CH)
Sum
check
code
Target device
Added value = 0327H
Contents of 0327H memory
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