AH500 Programming Manual
6-426
16-bit mode: The command which is edited is stored in the initial transmission device, and the
command which will be sent include the head code and the tail code. The 16-bit data is divided
into the high 8-bit data and the low 8-bit data.
Sending the data: (PLC→External equipment)
Receiving the data: (External equipment→PLC)
The data which the PLC receives from the external equipment includes the head and the tail
code. Therefore, users have to be aware of the setting of a length.
Additional remark:
1. There is no limit on the number of times the communication instruction COMRS can be
executed. However, every communication port can only be enabled by one communication
instruction, and the communication instructions which follow will not be executed.
2. The instructions which use communication ports are communication instructions, e.g. RS,
MODRW, FWD, and REV.
3. When COMRS is executed, no checksum is used. If users need a checksum, they can use
COMRS and another instruction available.
4. If the value in D
2
is 2, 3, 5, or 6, it is suggested that users should set a timeout period. After a
timeout period is set, the sending of data will be retried if a stop character is not received.
5. The instruction does not automatically clear the value in D
1
~D
1
+n whenever the instruction is
just executed or the PLC begins to receive new communication data. Only after a completion
flag is switched from OFF to ON can users know whether data is received, and how much data
the PLC receives. If the users want to clear the values in D
1
~D
1
+n, they can use the instruction
ZRST.
6. If the value in S
1
is neither 1 nor 2, the instruction will not be executed, SM0 will be ON, and
the error code in SR0 will be 16#2003.
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