Transmission Control Steps - Fuji Electric PXG-9 Communication Instruction Manual

Transmission Control Steps

Master Communication Method
Start communication from the master while following the rules below.
1. The command message, must be sent after an empty space of at least 48 bit time.
2. The interval between each byte in a command message should be less than 24 bit time.
3. After sending a command message, for less than 24 bit time the master will enter receiving standby.
4. After receiving the response message, the next command message must be sent after at least 48 bit time. (Similar to #1.)
5. For safety reasons, create a framework where the master checks the response message, and if there is no response or an
error occurs, retry at least three times.
The definitions written above are for the minimum required value. For safety reasons, we recommend creating a
Caution
master side program that keeps margins two to three times as large. For a concrete example, with 9600 bps, we
recommend programming a blank state (#1 above) of at least 10ms, and the interval between bytes (#2 above) and
switching time from sending to receiving (#3 above) within 1 ms.
Explanation
■ Frame Detection
This communication system uses a two-wire RS-485 interface, and the circuit can therefore enter one of the following two states.
Empty state (no data on the circuit)
•
Communication state (data running on the circuit)
•
The units connected on the circuit start in receiving state and monitor the circuit. When a blank state appears on the circuit for at least
24 bit time, the unit detects the end of the previous frame, and within the next 24 bit time, enters receiving standby. When data
appears on the circuit, the unit begins receiving data, and once another blank state of at least 24 bit time is detected, that frame is
ended. In other words, the data on the circuit from the first time that a 24 bit time blank state appears to the second time one appears
is loaded as one frame (a bundle of data). Therefore, one frame (command message) must be sent while following the rules below.
Before sending the command message, leave an empty space of at least 48 bit time.
•
The interval between each byte in a command message should be less than 24 bit time.
•
■ Micro controller Response
After the micro controller detects the frame (detects blank states at least 24 bit time long), that frame is used to send a command
message. When a command message is sent locally, the response message is returned, but the processing time is about 1 to 30
ms. (The time may change depending on the contents of the command message. ) Therefore, one frame (command message)
must be sent while following the rules below.
After sending a command message, for less than 24 seconds the master will enter receiving standby.
•
Interval of at least 5ms required
(at least 10ms recommended)
Master Slave
POL1
POL1 response data
POL2
POL2 response data
– 25 –
1 to 30ms
1 to 30ms
Chapter
5