Assignment of peripherals and pins
==================================

TIM1	timing of IR remote control
TIM2	MODBUS timing
TIM3	DS18B20 one-wire bus timing: CH1 drives DMA1, CH2 drives the line
TIM4	PWM: CH1 for fan control, CH2 for IR RC carrier

USART1	debugging
USART3	MODBUS

DMA1	DS18B20 one-wire bus sampling


			   Blue Pill pinout
			+--------------------+
			| VBATT		3.3V |
BluePill LED		| PC13		 GND |
			| PC14		  5V |
bypass opto-coupler	| PC15		 PB9 |
			| PA0		 PB8 |
			| PA1		 PB7 |	TIM4 CH2 - IR LED*
			| PA2		 PB6 |  TIM4 CH1 - fan control opto-coupler
			| PA3		 PB5 |
			| PA4		 PB4 |
			| PA5		 PB3 |
RS485 TX enable		| PA6		PA15 |
TIM3_CH2 - DS18B20 bus	| PA7		PA12 |
bypass LED* (green)	| PB0		PA11 |
MODBUS frame LED* (red)	| PB1		PA10 |  RXD1 - debugging console
TXD3 - RS485		| PB10		 PA9 |  TXD1 - debugging console
RXD3 - RS485		| PB11		 PA8 |
			| RESET		PB15 |
			| 3.3 V		PB14 |
			| GND		PB13 |
			| GND		PB12 |
			+--------------------+

Interface connector
===================

	(this side to PCB edge)

	heat exchanger +24V
	heat exchanger GND
	heat exchanger bypass servo
	heat exchanger fan control (IN1)
	-
	temperature sensors VCC
	temperature sensors GND
	temperature sensors data bus

	(this side to BluePill)