Blogs

MON0 routine and args.png

When calling a machine code subroutine from the Monitor, one or two additional arguments can be passed by taking advantage of the way the Monitor uses delimiters to parse arguments from its command-line and stores them in the zero-page pointers A1, A2, A3, A4...in an arbitrarily-strange order:

• The default argument is always the subroutine address, stored in A1.
• Appending a '.' delimiter allows another argument to be stored in A2.
• Inserting a '<' delimiter allows an argument to be stored in A4.

Clock stretching.png

Synopsis:

• Define a short datagram to be transmitted via vapor from visible screen memory.
• Encode single-cycle accurate video phase via vapor datagram.
• Construct a routine to receive the vapor datagram and synchronize itself to the video scanner.
• Write a simple BASIC program to demonstrate all that!

capture180 with numbers.png

Some experiments and variously messy results from trying to map how often the video scanner reads each byte of screen memory while creating each video frame.

Green indicates bytes that were detected only once per frame.

Purple indicates bytes that were detected twice per frame.

Orange indicates bytes that were detected thrice per frame.

Blue indicates bytes that were detected four times or more per frame.

Motorola TM2716 TI numbers.jpg

Early EPROMs required an unruly assortment of positive and negative power supplies, variously different programming voltages, an assortment of programming voltages.  And they adopted inconsistent part numbering schemes to distinguish these features.

Most surprisingly -- and irritatingly -- manufacturers gradually switched to elevated power supply voltages during programming.  So a 1977 Intel 2716 can be programmed with VCC=5 volts, whereas a 1988 AMD 2716 requires VCC=6 volts during programming.  And Texas Instruments's horribly-complicated TM2716 requires VCC=12 volts during programming!