Instruction manual

4
4. Communication procedure
Communication starts with command transmission from the host computer (hereafter Master) and
ends with the response of the PCD-33A (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 the 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 the negative
acknowledgement.
• No response
The slave will not respond to the master when global address
is set, or when there is a framing error or checksum error (for
Shinko protocol), or when LRC discrepancy (for Modbus protocol
ASCII mode) or CRC discrepancy (for Modbus protocol RTU
mode) is detected.
(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 interpreting the protocol.
5. Shinko protocol
5.1 Transmission mode
Shinko protocol is composed of ASCII codes.
Hexadecimal (0 to 9, A to F), which is divided into high order (4-bit) and low order (4-bit) out of
8-bit binary data in command is transmitted as ASCII characters.
Data format Start bit : 1 bit
Data bit : 7 bits
Parity : Even
Stop bit : 1 bit
Error detection : Checksum
5.2 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.
(1) Setting command
(Fig. 5.2-1)
Command
Data
Command
Acknowledgement
Command
Negative
acknowledgement
Command
No response
Master Slave
11 14 1241
Address
Command
type
(50H)
Data
item
Checksum
Delimiter
(03H)
Header
(02H)
Sub
address
(20H)
Data
Number of
characters