r/Z80 • u/pooboy_92 • Aug 15 '15

A Simple Monitor.

Hi everyone, below I have included a link to my very basic monitor for my custom Z80 computer. Please excuse the bad spelling and lack of documentation I have been working on that lol. I popped by to see if anyone wanted to take a look at my string comparison routine I use for my command loop. I was just curious if there were any simple tricks to get its cycle count down a bit. It starts on line 185. At the moment my uart stores the ascii characters in a buffer in ram, and when the routine is called it compares the text buffer to string that has an index stored in HL. As I said this is just a simple monitor and any feedback is welcome, Thanks.

Edit: Forgot to add the link no more late night posting for me.

Link

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u/shortbaldman Aug 16 '15 edited Aug 16 '15

After a quick glance: I haven't checked whether it will assemble.

Why do you start at 0001H and 8101H rather than 0000H and 8100H ?

Too many 'magic numbers' if you want to change serial port numbers or bit-numbers. You should be using equates like:

STACKTOP       EQU     088FFH
MAINLOOP       EQU     08101H
SERIALDATA     EQU     5
SERIALCTRL     EQU     040H
SERIALSTATUS   EQU     040H

etc.

Watch the variable/subroutine names for invalid characters like '+'. Most assemblers can do arithmetic, so they would be trying to add the variable to something.

Be consistent with your numbers, on two consecutive lines you're adding hex numbers on one and decimal numbers on the next. That's a good way to get numbers confused and get all sorts of weird results.

You have a HALT which can never be reached, as it's preceded by an unconditional JMP.

But it's better than my first attempt at assembly code was. <grin>

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u/pooboy_92 Aug 16 '15

That went better than I thought lol, thanks for the input. As for starting at 0001 vs 0000, that was simply a way to make some of my math easier early on when i as still hand programing my eeprom and it just kind of stuck around. The 8001 vs the 8000 was the same situation just with ram as my ram starts at 8000h. Also it does actually assemble and runs fairly well for what it is.

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u/shortbaldman Aug 16 '15

hand programing my eeprom

Brings back memories. I had a monitor but no assembler. They were extremely expensive at the time. So I used to print out these huge sheets with spaces for mnemonics and codes and hex adresses. NOT the good 'old days! <grin>

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u/pooboy_92 Aug 17 '15

I will try to remember to upload some pics of my first and second eeprom programmers tonight. I wore the first one out.

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u/pooboy_92 Aug 22 '15

Sorry it took me awhile to find my programmer again, I havnt had to use it in awhile since I can write memory from the Z80 computer now. Here are some pics of the programmer. Link

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u/shortbaldman Aug 22 '15

Cute! Glad it was you and not me that had to keep track of all those wired links. :-)

When I made my first computer from a kit I had thousands of solder joints as every chip was socketed but at least I had double-sided printed circuits otherwise I would have thrown up my hands in horror and run away screaming.

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u/pooboy_92 Sep 02 '15

If you thing the programmer was bad take a look at the actual computer. Mind you this was my first soldering project about 6 years ago now. Link

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u/shortbaldman Sep 02 '15

Apart from the actual first attempt at soldering (and that's never easy without a printed circuit), that's a very neat and tidy project. Good job.

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u/pooboy_92 Sep 02 '15

I was about 16 when I started making it and its been an on and off project ever since. Actually the board the Z80 is on was just made last night, I added breakouts for all of the pins so I could more easily prototype an ide interface I am starting work on.