Chintan, are you talking about 8 bit parallel data bus? or your data is coming in 1 byte (8 bit) packets?, not clear.
if you don't want to use microcontrollers, then, in plc you have to make ladders with timers, the timers need to be programed carefully to generate PWM pulses & accordingly, on every PWM o/p of timers turn on & off the o/p elements (servo i/p's, which will need a motor driver to take TTL level pwm o/p from plc & translate the logic levels matching to servo motor you are using), you need to study about the servo motor you are using, step size, voltage & current ratings, accordingly you have to put motor drivers which will finally
drive the servo motor.
about the matrix keypad, make 4 i/p's & 4 o/p's in ladder diagram and as Jean said you have to scan the 4 i/p lines continuously with a defined delay, you have to consifder a key denounce delay & confirmation routine to confirm the valid key pressed & finally get the hex codes for pressed keys. Connect keypad in multiplexed format, each column ise sourced by ext. dc voltage on board & connect series resistors according to the concerned PLC pin's sink current ratings. to generate the key debounce delays again you have use a timer API in you PLC ladder software.
you can use any cheap PLCs like AB - control logix 1000 (this work doesn't need high end featured PLCs) or semens S5 or any other vendor.
