Rev. 9

A project log for Novasaur CP/M TTL Retrocomputer

Retrocomputer built from TTL logic running CP/M with no CPU or ALU

Alastair HewittAlastair Hewitt 06/23/2021 at 01:510 Comments

Rev. 8 was supposed to be the final "pre-release" board, but a few minor updates turned into a fairly major refactor of the power distribution. The result has been impressive...

Note: these photos greatly exaggerate the background power supply ground noise. This isn't exactly what it looks like under normal viewing, but the it is very noticeable on this monitor when viewed from above (the photos also have a filter to increase the contrast).

The first photo is from the Rev. 8 board and the periodic noise from the ground plane is very noticeable (even this was an improvement from the Rev. 7 and earlier boards). The second photo is the Rev. 9 and the periodic noise is almost gone.

There is still a high frequency component modulated with a period matching the horizontal frequency. It rises to a peak in the center of the screen and looks like a CRT phosphor burn... an unexpected but very cool retro effect!

There were three component changes - the volume control and reset button have been added back. These aren't really necessary, but it's more fun to have extra knobs and buttons to play with. The other change was ditching the super caps and switching to a battery. The super caps could backup the memory for almost a month, but a CR2032  can last up to 5 years.