A0  <-  pressure sensor  
A2  <-> one wire bus
A11  -> yellow LED (OD)
A12  -> green LED 1 (OD)
A15  -> green LED 2 (OD)

B1   -> PIC RESET
B3   -> red LED (OD)
B6  <-  PIC B6 LED_C (from A0, OT from thermostat)
B7  <-  PIC B7 LED_D (from A1, OT from boiler)
B8   -> PIC A6 GPIO_A (to A3, OT to boiler)
B9   -> PIC A7 GPIO_B (to A4, OT to thermostat)
B10  -> PIC RX
B11 <-  PIX TX

C13  -> onboard LED (OD)

A2   -> MR3020 TX
A3  <-  MR4020 RX 
RST <-  MR3020 GPIO5