Modifying Tape Loader/Saver (Video 26)

General discussions related to the Altair 8800 Clone

Modifying Tape Loader/Saver (Video 26)

Postby kwiebe » March 17th, 2019, 8:46 pm

Hi,

Video 26 deals with loading and saving the front panel Pong program. In the support doc,

http://altairclone.com/downloads/pong.pdf

the loader and saver programs are listed along with the "octal dump for front panel entry."

The programs were written to utilize the SIO port (address 0/1). I'm wondering how to change them to use the 2SIO at 20/21.

I see in the program listing for the SIO the first two instructions reference 0/1. So I want to change those to 20/21. But what I'm not getting is how that would change the octal dump for the front panel. Can someone explain how to do this?

More generally, what's the relationship between a program and the octal dump of a program?
-Ken
kwiebe
 
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Re: Modifying Tape Loader/Saver (Video 26)

Postby TronDD » March 17th, 2019, 9:26 pm

The octal dump is just the assembled op codes and parameter values ( shown in hex in column 2) converted to octal.

Changing these programs to use the 2SIO port is more complicated than changing the addresses. And changing the octal means you're assembling the code by hand.

The 2SIO requires you to configure the port where as the SIO was hard coded. Adding this code means you'll shift the addresses of all the labels so you'll have to update all the jumps.

These are small programs so they would be easy to start with but you'll have to learn the 8080 opcodes and learn what the assembler does in order to hand assemble to the octal yourself. This is how I've been doing all my Altair programming. Read the "8080 Programmer's Manual" available in the Altair Manuals support package.
TronDD
 
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Re: Modifying Tape Loader/Saver (Video 26)

Postby kwiebe » March 17th, 2019, 9:34 pm

Thanks for the info and pointers...I'm learning!
-Ken
kwiebe
 
Posts: 51
Joined: February 9th, 2019, 1:11 pm


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