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12.4 Communication procedures
Communication starts with command transmission from the host computer (hereafter Master) and ends
with the response of the KT4H/B (hereafter Slave).
• Response with data
When the master sends the reading command, the slave
responds with the corresponding set 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 a 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 in the following cases.
• Global address “FF” (MEWTOCOL) is set.
• Broadcast address (Modbus protocol) is set.
• Communication error (framing error, parity error)
• LRC discrepancy (Modbus ASCII mode)
(Fig. 12.4-1)
• CRC-16 discrepancy (Modbus RTU mode)
Communication timing of the RS-485
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.
Slave side
When the slave starts transmission through the communication line, the slave is arranged so as to
provide an idle status (mark status) transmission period of 5ms or more (communication response time
from 5 to 99ms settable) before sending the response to ensure 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.
Command
Data
Command
Acknowledgement
Command
Negative
acknowledgement
Command
No response
Master
Slave
