Teletype output decoder

Decoded only 4 LS bits of the output value:

0-9 - digits
A-E - not used
F - carriage return

Teletype input register

Reads 4 LS bits of the key pressed on the teletype. Also sends INT signal to the Control block, which allows to continue program execution, when CPU is halted.

Keys 0-9 are read as values 0-9.