7
4. Communication procedure
•
RS-232C (option C), RS-485 (option C5)
Communication starts with command transmission from the host computer (hereafter Master) and
ends with the response of the PC-900 (hereafter Slave).
• Response with data
When the master sends the reading command, the slave
responds with the corresponding setting value or current
status.
• Acknowledgement
When the master sends the setting command, the slave
responds by sending an acknowledgement after the
processing is terminated.
• Negative acknowledgement
When the master sends non-existent command or value
out of the setting range, the slave returns a negative
acknowledgement.
• No response
The slave will not respond to the master when there is
a framing error or checksum error.
(Fig.4-1)
Communication timing of the RS-485 (option C5)
Slave side
When the slave
starts transmission to RS-485 communication line, the slave is arranged so as to
provide an idle status (mark status)
transmission period of 1 or more
characters
before sending
the response to ensure the synchronization on the receiving side.
The slave is arranged so as to disconnect the transmitter from the communication line
within a
1 character transmission
period
after sending the response.
Master side (Notice on programming)
Set the program so that the master can disconnect the transmitter from the communication line
within a 1 character transmission
period
after sending the command in preparation for reception
of the response from the slave.
To avoid the collision of transmissions between the master and the slave, send the next command
after carefully checking that the master received the response.
Note:
When the master communicates with the slave through the line converter (IF-300-C5), it is
not required to manage the transmission timing described above, because the converter
automatically sets the transmission timing while interpreting the protocol.
(See pages 5 and 6 for RS-485 connection.)
5. Command configuration
5.1 Command configuration
All commands are composed of ASCII. The data (setting value, decimal number) is represented by
hexadecimal figures, and ASCII code is used.
The negative numbers are represented by 2's complement.
(Example)
Decimal number
Hexadecimal figure
9999
270FH
1000
03E8H
100
0064H
1
0001H
0
0000H
-1
FFFFH
-100
FF9CH
-1000
FC18H
-1999
F831H
Command
Data
Command
Acknowledgement
Command
Negative
acknowledgement
Command
No response
Master
Slave
