Rev 5.8
SignalFire Telemetry
9
RS-485 Modbus Communication
Communication Settings
The Sentinel Modbus needs to have its serial RS-485 parameters set to match the device
it’s communicating with. Default settings are a baud rate of 9,600bits/s, UART mode 8N1
(8 data bits, No parity bit, 1 stop bit), command
timeout of 1000ms, and command pause of
100ms. This should be sufficient for most devices,
but check your device’s datasheet to confirm.
Note that the Gateway and Sentinel’s RS-485 settings are unrelated and do not need to match.
Modbus Program Steps Configuration
The register set to poll on each check-in must be
defined using program steps. The Sentinel Modbus
can have up to 34 program steps. A program step
consists of a function code, starting address,
number of consecutive registers, and register size.
Possible function codes are:
0x01: Read discrete output (limit: 1 coil)
0x02: Read discrete input (limit: 1 coil)
0x03: Read holding register
0x04: Read input register
0x05: Write discrete output
Click
Read Steps from Sentinel
to view the current
program steps in the table. To add a new program
step, fill in the next empty line. To delete a step,
click on the line number and press the Delete key.
Lines can also be copy/cut and pasted. Once all the
desired program steps have been entered, click
Write Steps to Sentinel
to save the changes.
The Slave ID should match the ID of the connected
Modbus device. Make sure that there are no duplicate Slave IDs in a given network; the gateway will
only cache one set of data for each Slave ID, so the duplicate will be overwritten.
The register address entered is subtracted by the offset in the Register Addressing Mode. The offset
can be 0 or 1. For example, with One Based Addressing, a holding register of address 3990 should be
entered as function code 0x03, address 3991. Keep in mind that one 32-bit floating point register
