GC1100 SEDEMAC
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Communications Protocol
Introduction to Communication Protocol
GC1100 genset controller support two communication protocol: a custom protocol based on MODBUS
over a RS485 layer and a custom protocol over a CAN layer.
RS485 MODBUS Based Protocol
GC1100 genset controller implement a custom protocol based on standard MODBUS protocol. It
operates in a slave mode and responds to commands received from an external MODBUS master. The
details of the protocol are as shown below.
12.1 Connection Details
The RS485 port on GC1100 controller supports the MODBUS RTU protocol.
The format for communication of each byte is as follow:
1 start bit, 8 data bits, least significant bit sent first, 1 parity bit for even/odd parity; no parity bit for no
parity, 1 stop bit, Cyclical Redundancy Check (CRC).
Figure 20: RS485 MODBUS connection with the help of two core shielded twisted pair cable
The transmission mode used by GC1100 controller is MODBUS RTU (not
MODBUS ASCII). The byte format for communication is 1 start bit, 8 data bits,
with/without parity bit and 1 stop bit. The baud rate is selectable between 1200
kbps to 115200 kbps through the configuration options. Similarly, the slave ID can
be selected through the configuration options.
RS485 MODBUS communication configuration setting is as shown in Table 30
Table 30: RS485 MODBUS communication configuration setting
1200/2400/4800/9600/19200/38400/57600/115200
SEDEMAC GC1100 genset controller operates as a MODBUS slave that responds to certain
commands received from the MODBUS master.
RS485 MODBUS communication is initiated by a Master with a query to a Slave. The Slave which is
constantly looking for Queries from master will recognise only the Queries addressed to it and will
respond either by performing an action or by returning a response. Only the Master can initiate a query.
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