Writing Position Independent 8080 Code

General discussions related to the Altair 8800 Clone

Writing Position Independent 8080 Code

Postby AltairClone » January 15th, 2016, 4:15 pm

The 8080 doesn't support position independent code other than by using some ugly tricks. However, there are times when these ugly tricks may be considered worth it.

I have created an Intel hex file loader for the Altair that fits in a 256 byte PROM (e.g., 1702a or bigger). What is unique about this PROM is that it will run, without modification, at no matter what address in the machine the PROM is installed. In addition, it sizes RAM and automatically relocates itself and its stack into high memory. This means the PROM can be installed in most any machine wherever an open PROM socket is available, and without worrying about whether RAM is present where a PROM might happen to expect it. Typically, code like this would have to be re-assembled and a new EPROM burnt after changing the code and stack addresses as required.

See "HEXLOAD.ASM" in the http://altairclone.com/downloads/roms/ folder.

Mike
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