|
|
CAPC - Part 8 |
Wiring the ADD instruction looked brutal and I still hadn't gotten around to putting in the JMP and JMI instructions so I decided to do them first. I dug around on the course website until I found some instructions for installing JMP. It took about 10 minutes. JMP is the unconditional-jump instruction which moves the point-of-execution to a new address in memory. Essentialy, it is the "goto" command.
JMI is the conditional-jump instruction. It provides a new address in memory to jump the point-of-execution to, but the jump should only occur if the condition is true. The condition in this case is that the highest bit of the general register (GREG) be true. This was a little trickier. I needed the Q15 signal from the general register (GREG). But I didn't want to apply the 'send' signal and have GREG clogging up the bus. So I created a 16-bit buffer and put it in place. Then I was able to tap the line between the register and the buffer. I put the Q15 signal from GREG onto the signal bus so I could access
it easily from a couple of places further up the processor. I named the
signal GREG15. With the GREG15 and JMI signals on the signal bus it was easy to setup
a couple of AND-3 gates to perform the JMI instruction logic.
|
