Appendix D. Modbus; Protocol; Supported Modbus Commands; Connections Settings - Geokon 8800-2-1A Instruction Manual

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APPENDIX D. MODBUS

D.1 Protocol
The Supervisor protocol is Modbus RTU. Information about Modbus can be found here:
http://www.modbus.org/specs.php
D.2 Supported Modbus Commands
Modbus was originally developed for communicating with programmable logic controllers.
Many Modbus commands do not make sense with respect to modern embedded devices. GeoNet
Supervisors utilizes four commands:
(0x03) Read Holding Registers
(0x04) Read Input Registers
(0x06) Write Single Register
(0x10) Write Multiple Registers
D.3 Connections Settings
115.2 kbps, eight data bits, one stop bit, no parity, no flow control.
D.4 Special Considerations for GeoNet
GeoNet is an ultra-low-power network. More than 99% of the time, the devices that comprise the
network are in deep sleep. Master devices must recognize busy responses and retry. On first
communication, a busy response is almost a certainty. The Supervisor will stay awake for one
minute after the last communication to be more responsive if subsequent requests are made.
D.5 System Info Table
The system info table provides basic metadata as well as the network time. A newly powered
network will not start acquiring data until the time has been set. This can be accomplished with
Agent software or by writing the time to addresses 0xE20-0xE22. The time does not persist
through battery replacement.