Microprocessor Lab - Microprocessor Programming and Opcodes –
Add Ready Signals
Physics 335
May 8, 2007
In this lab, you will finish wiring an input port to allow the CPU to read the keypad (defined
as memory address $ 8000 by the HCT 138 you installed in the last lab). You will also wire
in a READY SIGNAL (A one bit signal from memory location $ 8001 that tells the CPU when
the keypad has new data. The wiring this week is relatively quick. The rest of the time will be
programming to make use of some of the features we’ve included in the past weeks. NOTE: For
the first time, you will have to work out some of the instruction opcodes for yourselves. Be sure to
try to understand the programs as you use them.
A note to those of you behind. You should try to catch up as soon as you can. Time is available
on Monday and Friday mornings for you to work outside of class hours if you arrange it with your
TA. If, at this point, your processor is not executing opcodes and loops, you are behind enough that
you should consider taking advantage of this. Next week will be a miniproject, showing you know
how to use the processor and opcodes. There may be some catch up time as well, but if you’re too
far behind, it won’t be enough.
Another note – Keep in mind that the example circuit is wired and working through the end of
today’s lab – If you’re behind, or even working on an earlier section, you should wire as instructed
in that section. DO NOT blindly copy off the front example board, especially if you are not as far
along as that board is, as each step along the way has changes, and sometimes previous wirings
needed for an earlier section are removed as we get successive “small pieces” working. Mixing and
matching parts from earlier and later sections may lead to intersting results. While it may seem
obvious to most of you, it should be noted that your microprocessor board is a SYSTEM and all
the parts must work together correctly. The lab writeups will walk you through that process if you
follow each and every step in the order it appears, testing the new parts along the way. Not doing
so, however, or inventing your own procedures may lead to some remarkable confusions. Do so at
your own peril. And randomly changing wiring is not likely to lead to a productive conclusion –
You must trace an input from what you know is good through the circuit until something doesn’t
make sense... And there will very likely lie your error. You should follow the steps outlined in the
order outlined until you have a good understanding how the parts fit together, then you can make
your own changes intelligently when it comes to project time.
Section 20-1 - p. 489 Do this section as described in the manual. Be sure the first 8 memory
locations contain in order 00 00 20 00 00 00 01 00 to specify the address of the stack to be $
00002000 and the address of your main program to be $ 00000100.
You need to fill in the op codes for the branch instructions where you see the “xx”. We’ll do
them for you here but not for the later sections. At memory location $010E you need a BSR ’Delay’
instruction to $0166, the address of the delay subroutine. The offset is then the hex difference $166
- $110 = $56. When the offset is only one byte (always two’s complement), you can use a single
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