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Example 2: Memory access with handshaking
Use a serial data unit to perform a self-looping communication via the RS232C interface "CH1".
The unit performs handshaking using the input "X" contacts and output "Y" contacts for data
communication.
1) Sending the data stored in DT100 to DT114 (15 words) of the CPU via CH1 of the serial data unit
installed on slave station.
2) Data sent from CH1 will be received at the same CH1 of serial data unit.
3) Read teh ata received at the CH1, and the data will be stored in the DT200 to DT214 of the CPU.
Program the above operaiton.
When programming, note the following.
1. Be sure to examine the program for memory access instructions so that the control transfers to the
next access only while R9035 is ON.
2. When you use a serial data unit on the [MEWNET-F], be sure to create the program taking the
ON/OFF timing of the control relays (X or Y) into considerations.
(Example) Program for performing handshaking smoothly
There are some differences in the operations between the normal memory access instruction F150/F151
and the memory access instruction F152/F153 for the advanced unit on a slave station.When executing
the memory access instructions F152 or F153, not the following:
Operation of F150/F151
When an F150 or F151 instruction is executed, the CPU access to the advanced unit is performed at the
moment that the instruction is executed. With this operation, the serial data unit's handshaking control
can be performed with programming the control relays (X or Y) at the higher step address.
Operation of F152/F153
When an F152 or F153 instruction is executed, the CPU access to the master unit is performed at teh
moement. However, the data transfer between the master unit and the advanced unit are performed
after the End instruction.While this operation, the serial data unit's handshaking control should be
performed after the special relay R9035turns ON.
3. Since two or more F152/F153 instructions can not be performed at one time, the program should be
created not to execute two or more F152/F153 instructions at a time with using the special relay R9035
and step laddar instructions.
8-11
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Troubleshooting
