17: USER COMMUNICATION INSTRUCTIONS
17-20 OPENNET CONTROLLER USER’S MANUAL
Comparing BCC Codes
The OpenNet Controller compares the BCC calculation result with the BCC code in the received incoming data to check
for any error in the incoming communication due to external noises or other causes. If a disparity is found in the compari-
son, an error code is stored in the data register designated as receive status in the RXD instruction. For user communica-
tion error code, see page 17-25.
Example 1: BCC is calculated for the first byte through the sixth byte using the XOR format, converted in binary to
ASCII, and compared with the BCC code appended to the seventh and eighth bytes of the incoming data.
Example 2: BCC is calculated for the first byte through the sixth byte using the ADD format, converted in binary to
ASCII, and compared with the BCC code appended to the seventh and eighth bytes of the incoming data.
Receive Completion Output
Designate an output, Q0 through Q597, or internal relay, M0 through M2557, as an operand for the receive completion
output.
When the start input for a RXD instruction is turned on, preparation for receiving data is initiated, followed by data con-
version and storage. When a sequence of all data receive operation is complete, the designated output or internal relay is
turned on.
Conditions for Completion of Receiving Data
After starting to receive data, the RXD instruction can be completed in three ways:
• When an end delimiter is received (except when a BCC exists immediately after the end delimiter).
• When receive timeout occurs.
• When a specified byte count of data has been received.
Data receiving is completed when one of the above three conditions is met. To abort a RXD instruction, use the user com-
munication receive instruction cancel flag M8022 or M8023. See page 17-21.
“1”
(31h)
“2”
(32h)
BCC Calculation Range
“3”
(33h)
“4”
(34h)
Incoming Data
“5”
(35h)
“6”
(36h)
“0”
(30h)
“7”
(37h)
BCC
31h ⊕ 32h ⊕ 33h ⊕ 34h ⊕ 35h ⊕ 36h = 07h
“0”
(30h)
“7”
(37h)
BCC Calculation Result
Binary to ASCII Conversion
Comparison result is true to indicate
that data is received correctly.
“1”
(31h)
“2”
(32h)
BCC Calculation Range
“3”
(33h)
“4”
(34h)
Incoming Data
“5”
(35h)
“6”
(36h)
“0”
(30h)
“7”
(37h)
BCC
31h + 32h + 33h + 34h + 35h + 36h = 135h
“3”
(33h)
“5”
(35h)
BCC Calculation Result
Binary to ASCII Conversion
Comparison result is false.
Error code 9 is stored in the receive
status data register.
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