DL8000 Preset Instruction Manual
Revised February-2016 Modbus Communications B-19
B.6 Modbus Master Table
The Modbus Master mode allows the DL8000 to simulate a master
device that can poll other devices for data and to store the data for
parameter updates, for use in FST program registers. The DL8000 can
also send commands to set outputs and write data to a slave device.
Note: You can configure Modbus master functionality only for the
EIA-232 (RS-232), EIA-485 (RS-485), and modem
communications ports (Comm 2 through Comm 5). The LOI and
Ethernet (Comm 1) ports do not support Modbus master
communications.
You can configure up to 200 different master requests/commands across
communication ports Comm 2 through Comm 5. Each command can
transmit or receive up to 240 bytes of data.
The system supports Modbus Function Codes 1, 2, 3, 4, 5, 6, 15, and 16.
Function Codes 1 to 4 request data from slave devices, while codes 5, 6,
15, and 16 transmit data to a slave device. See Table B-7.
Table B-7. Modbus Function Codes
01 Read Logic Coil Status
Obtain current status (ON/OFF) of a group of logic coils
(outputs).
02 Read Discrete Input Status Obtain current status (ON/OFF) of a group of Discrete Inputs.
03 Read Output Registers (Holding) Obtain current binary value in one or more holding registers.
04 Read Input Registers Obtain current binary value in one or more input registers.
05 Force Single Logic Coil
Force logic coil to a state of ON or OFF. Acknowledge Alarm
or Event request.
06 Preset Single Holding Register Place a specific binary value into a holding register.
15 Force Multiple Logic Coils
Force a series of consecutive logic output coils to defined ON
or OFF states.
16
Preset Multiple Holding
Registers
Place specific binary values into a series of consecutive
holding registers.
Each master request you configure must have a corresponding entry in
the Modbus Registers table. When using Modbus Function Codes 1 to 4,
the DL8000 reads data from a slave device and writes it to the TLP
specified in the Modbus Registers table. When using Modbus Function
Codes 5, 6, 15, and 16, the DL8000 reads data from the TLP specified
in the Modbus Registers table and writes it to the slave device.
As a Modbus master, the DL8000 may have to communicate to multiple
slave devices through modems and phone lines. The Modbus Master
Modem screen provides the necessary parameters to configure the
modems and map RTU Addresses to phone numbers. One
communication port has the ability to dial-up six different Modbus
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