S.Elliott's blog

Clumsy (but pretty!) attempts to map video scanner's memory access

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.

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Upgrade the Disk II controller with shrouded headers

Apple chose bare headers for the disk connectors on the Disk II controller, which make it notoriously easy to connect the drive cable incorrectly.

Jameco's "Shrouded Box Header 20 Pin 2316R-20G" makes an ideal replacement.

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The chaotic shambles of EPROM voltages, from 2708 through 2764

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!

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