M1
M2
M3
M4
M5
M6

S1
S2
S3
S4

CS1
CS2
CS3

VSENS

V_PV
PWM_PV

CAN (over SPI) (3)
RTC (over I2C) (2)

6 DO
4 DI
1 PWM
5 AI
5 COMMS

-> 16 DIO

might be able to use a shift register to reclaim pins?

ATmega328P has 14 DIO and 6 AI

ATmega1284P exists
Atmega2560 is top dollar