Manual – Starflow QSD Model 6527B and 6537A
Unidata Manual - 6527B and 6537A Starflow QSD User Manual 17 01 2020.docx
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4.2 Modbus RS485 Operation
The Starflow QSD can be operated as a Modbus RTU Slave sensor. The Baud rate and parity
selected must be configured prior to using the instrument. The instrument supports configurable Baud
rates for the RS-485 Communication Port (the SDI-12 Port is fixed to 1200/9600 as per the SDI-12
standard). There are two configuration parameters (baud rate & parity) and these may be changed via
the Sonic configuration utility (via Modbus).
When changing these, the new settings come into effect AFTER the response has been sent to the
SONIC/Modbus PC utility. To continue communicating via RS-485, the PC utility’s baud rate settings
MUST then be changed to match that of the Starflow QSD.
Use the “SETTINGS/Configure SONIC” menu to change baud rate settings, and then click
"CONNECT" to re-connect.
Note 1: SONIC ALWAYS starts in 9600,8,N,1 when launched in Windows.
Note 2: If a HARD FIRMWARE UPDATE (QSD Serial# set to zero) is performed over RS-485 at a
baud rate other than 9600, the update will succeed, but indicate failure because the existing RS-485
baud rate settings are not preserved across a hard update and have been reset to the default 9600.
RS485 Baud rate and Parity setting options can be configured using PC SONIC utility via Unidata
6603W FTDI programming cable OR using a USB to RS485 Converter Cable.
RS-485 Baud Rate Settings
(0..4)
0 = 9600
Default
1 = 19200
2 = 38400
3 = 57600
4 = 115200
RS-485 Parity Settings
(0..5)
0 = 8,N,1
Default
1 = 8,0,1
2 = 8,E,1
3 = 8,N,2
4 = 8,0,2
5 = 8,E,2
4.2.1 Reading the measured parameters via Modbus
Physical links requirement: RS485 - low power, 2V, three wire (A/B signals & ground), differential, half
duplex; at 9600bps (support up to 1000m cable, at 19200bps up to 500m cable, at 115Kkps up to
100m cable) and it supports PP, MD & MP protocols.
Protocol requirement:
MODBUS (Modicon) - variable speed (9600 & 19200), MD over RS485. For PC
configuration, an USB to RS485 converter is required. The instrument has to be powered via 12V and
ground; A- and B+ signals will need to be connected as per wiring table in specifications section 2.0.
The instrument supports the
Modbus RTU communication protocol
; this is the format of choice for
serial communications such as RS485/RS232 as it is the most efficient.
The general message structure will consist of device address, function code, data payload and the
checksum.
