M&M
R
EFRIGERATION
I
NC
. C-7
Appendix C: Software Interface Description
Software Interface Description
Protocol Overview
All communications with the M&M screw controller is on a request-response basis. The
main computer is the “master” and the M&M controller is the “slave”. All messages will
originate on the master with the slave responding as required.
Status Only or Status and Control Options
The screw compressor microprocessor communications supports two options. When con-
figured for the Status Only option, the CCS will only respond to the status message but
will not respond to any control or setpoint messages. When configured for the Status and
Control option, the CCS will respond to all message types.
The Status and Control option is selected using dip switch SW2 Switch 1 on the main
microprocessor board (Network Control Option). When the Network Control Option dip
switch is OFF, Status Only is selected and an error response will be returned whenever a
control message is attempted. When the Network Control Option dip switch is ON, Status
and Control is selected and control messages may be used to control the compressor.
The Remote and Auto-Remote modes are the primary means of control when the Network
Control Option is enabled. The Remote option is selected using dip switch SW2 Switch 4
and the Auto-Remote Option is selected using dip switch SW2 Switch 5.
Message Categories
No matter which protocol is selected, several message categories are supported and
described below:
• Status Message
• Compressor Control Message
• Suction Pressure Setpoint Message
• Process Temperature Setpoint Message (Optional)
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