Obviously, In-System Programming for flashing

JTAG interface for step-by-step debugging - very powerful tool. One can freeze the processor and read the real inputs from the processor's pins

RS232-1 and RS232-2 - these two are present, They do not have a standard connector due to lack of space, but the circuitry is there and the USART can be used. The junction to a standard connector is an option.

Two-wire Serial Interface to connect to expansion processor boards, ADCs, DACs, etc

Pins for external control (motor, rele, etc), ADC, expansion of IR emitters and receivers, external interrupts