9-2 Qualitek mR Owner’s Guide
9.1.2 Modbus Communications
The QmR external communications serial port can be configured for use as an RS-
232 transceiver. The table below summarizes the standard configuration and
options.
9.1.3 Supported Modbus Functions
The QmR provides the Modbus master (host system) with access to many
functions that would be available to an operator for selecting, starting, and
controlling a test, as well as obtaining results and status information, along with
history.
The QmR supports the RTU (Remote Terminal Unit) Modbus transmission mode
with the characteristics outlined in the following table.
Standard Configuration Options
RS-232 None
Full-duplex, no hardware handshaking, 9600
baud
1200 to 57600 baud w/ or w/o hardware
handshaking
8 data bits, no parity, 1 stop bit
Modbus functions Type of data
Read
Write
(single)
Write
block
Location
reference
Modbus
description
QmR usage
Field
size
1
1.Number of bytes in RTU (binary) mode.
1 5 15 0xxxx Coils Global commands and
settings
1
2
2
2.Digital inputs and input registers are read-only; there are no Modbus write functions for those registers.
1xxxx Digital inputs Inputs, Events, & Status 1
3 3xxxx Input registers Test results and status 2
4 6 16 4xxxx Holding
registers
Test selection, control 2
Transmission
Mode
Beginning of
message
frame
Data format Error check End of frame
RTU Silence 8 bit binary
CRC
1
1. CRC = Cyclical Redundancy Check
Silence
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