The purpose of this document is to define the requirements for a new firmware development of a Control Interface for HVAC units.
This interface acts as a MODBUS slave interface, at fixed speed (115.200bps)
There are 4 modbus registers to identify the model, type, serial number and the modbus address. Modbus address can be modified for the master, but only applies after a Reset. Default address is 1.
There is also a fixed broadcast address 255 for master commands, no answer is required.
There are also 4 registers more: 3 for operation and 1 for status & alarm code:
There are two PCB designs: one for BASIC or WATER HVAC unit and the other for ELECTRIC HVAC unit, so there are 3 different firmware:
1) BASIC HVAC UNIT:
a. Switch ON AC supply when all is ok, switch off in case of alarm
b. Fan speed control: low / fast / stop (2 digital lines). Very important: changes in speed must be synchronized with ZCD input signal
c. ZCD signal control, corresponding to AC line frequency. Alarm if it’s out of normal range (50/60 Hz)
d. 2 input digital signals & 1 output signal for users app.
e. 1 PTC1000 temperature sensor, for user info
f. Led Indicator Status/Alarm: fast blink during communication and slow blink for alarm codes.
2) WATER HVAC UNIT:
The same than 1) but adding EV relay digital output signal
3) ELECTRIC HVAC UNIT:
The same than 1) but adding Heat Control system:
a. 3 output signals for control 3-stage heater. Heater cannot switch on if fan is stopped. Heater stage can be selected as function of fan motor speed and model/type, following the next table:
Speed Max heater
OPT 1000 9kW Max heater
Stopped 0 (no heater) 0 (no heater)
Low 2 3
High 3 3
b. Overheat sensor (NO) digital input. Generate alarm & increase fan speed every 2 minutes. After this, Heater must be stopped. When overheat signal disappears, heater must be restored to the programmed stage.
• PLANNING & MILESTONES
2 hardware units supplied: BASIC/WATER CONTROL INTERFACE and ELECTRIC CONTROL INTERFACE, to be used as for debugging the new firmware design, with a programmer tool for ST8M family microcontrollers
Proposal phases / milestones of firmware project:
1) “Hello World” STM8 and peripherals (UART)
2) SLAVE MODBUS communication protocol
3) Basic/Water control interface firmware design
4) Electric control interface firmware design
• embedded systems
• c programming
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Hello,Myself [login to view URL] Sekhar,[login to view URL],Phd from Cdeec Innovations,[login to view URL] have 15+ years experience in Electronics Product development. we have in house pcb fabrication facility for protoypes.i have worked on many IO Lagi