Whilst it is very straightforward in assembler as mentioned, it doesn't make for very portable code

The illusion that I/O code for small micros has any chance of portability evidently still pervades.

If it is processing for some (companywide) universal purpose, yes, portability is "interesting", but for code related to I/O, portable my ...

I have hunks of code that I will some day transfer from a '51 to likely an ARM and all processing is thus written in "portable" C, portable in quotes cause the will be some porting effort required. However all I/O is written with no concern for portability since I have yet to see any such being possible.

I have, however found one interesting means of portability of I/O code: strip all code, leaving the comments, and recode for the new micro with the comments as a template.

Erik