Currently I have this 4 bit CPU as shown in the schematic diagram below. enter image description here

What I wish to achieve:

  • Add one more output register to make the CPU output a total of 8 bits
  • Show alphabet using the 8 bits output

My current trial:

  • Cout of the first IC connected to Cin of the second IC
  • Cascaded in synchronous fashion enter image description here

What I unsure/don't understand:

  • Should I connect the A~D pins of the second register to ALU?
  • The LOAD-bar pin is connected to LO-bar of the ALU. Should I add one more LO-bar to the ALU and connect it to the LOAD-bar of the second register?
  • \$\begingroup\$ Is this a working design? There are lots of unconnected pins and why use counters for registers, especially the outputs? \$\endgroup\$ – Finbarr Jul 27 at 11:09
  • \$\begingroup\$ The first diagram is a 4 bit CPU schematic diagram given by my lecture, so I assume it is a working one. The second diagram is just my trial, which I am not sure how to cascade the two to get 8 bits from it. \$\endgroup\$ – sttc1998 Jul 28 at 3:16
  • \$\begingroup\$ As it stands this question is unanswerable. It needs a lot more detail on how things are connected (e.g. the three inputs of the 74HC161 that aren't shown that are key to its operation) and more detail on what the actual task is. What does "show alphabet" mean? Voting to close as unclear. \$\endgroup\$ – Finbarr Jul 28 at 10:41
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    \$\begingroup\$ The actual task is to improve the 4 bit CPU given in the first schematic diagram. So I wonder can I add one more 74HC161 to get 8 bits output instead of only 4 bits. May I know what are the three inputs that are key to 74HC161 operation? \$\endgroup\$ – sttc1998 Jul 28 at 10:47
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    \$\begingroup\$ Find a 74HC161 datasheet and read it, specifically the Mode Select function table. "Improve" is not a specific task, you need a full understanding of what it does and what you want to change. You can add extra outputs to anything but making them do what you want is the hard bit. \$\endgroup\$ – Finbarr Jul 28 at 10:51

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