10x 74hc191 synchronous binary up/down counter - 4 are being used for the stack pointer
Stack pointer uses 4 counters, high and low byte SP-H, SP-L
Control signals:
High byte in, high byte out
low byte in, low byte out
Stack pointer count enable
Stack pointer up/down signal
6 signals total
can use a 3-8 decoder
(BLANK, high in, high out, low in, low out), stack count enable, stack pointer up/down
<!– 30x BC327 PNP transistors - for multiplexing outputs - common anode
30x BC337 NPN transistors - for multiplexing outputs - common cathode –>