I Data inputs. These data may be selected as one of the ALU sources. The address inputs to the register stack, used to select which register's contents are available through the A port. The address inputs to the register stack used to select which registers contents are available through the B port. I O The input and output of shift lines for the LSB and MSB of the Q register.
Dual lines allow for shift up and shift down operations with out tri states.
Q0O is valid when OE0N is low and Q3O is valid when OE3N is low. O Becomes active when all four ALU outputs are low. The most significant ALU output bit. The generate and propagate outputs of the ALU, can be used to for cary-lookahead. OVR O Overflow.