Multi-Tech Systems 7500 - Manual (Page 215)

ION 7500 / ION 7600 User’s Guide Expansion Boards for Meters with Modbus Master Capability
Digital and Analog I/O Technical Note Page 215
Power Requirements
The Modbus controller requires 1 Amp at 5Vdc. The I/O modules require between
10-150mA depending on module type.
The 5-Amp power supply can support the Modbus controller (1 Amp) plus two
full racks of digital I/O that fit on a DIN rail rack.
Communications Considerations
The OpenDAC controller provides four wire RS-485 with the Modbus RTU
protocol. To get two additional RS-485, connect a jumper wire between the two
negative and positive terminals.
The Unit ID is set with two dial switches. One switch sets the low word of the ID
(0x0 to 0xF) and the other sets the high word. Protocol and baud rate are set with
the third dial switch, common settings are as follows:
N OTE
Detailed setup information for the Grayhill OpenDAC system is available at www.grayhill.com and in
Bulletin #812, OpenDAC Modbus Configuration, Installation and Troubleshooting manual. Part
numbers are available on the Power Measurement order form.
Description Maximum draw per channel for I/O
Controller 1A
Rack 40mA
Digital Inputs 20mA
Digital Outputs 20mA
Analog Voltage Input 75mA
Analog Current Input 75mA
Analog Voltage/Current Outputs 200mA
Thermocouple Modules 75mA
Switch Setting Parameters
0 9600 baud Modbus RTU
1 19 200 baud Modbus RTU
Remaining settings are for higher baud rates or ASCII protocol