*** M E M O R U M ***

Just for confirmation, the current prototype board connects via the 20 pin header, so there's direct access to: KB9 to KB0 DR0 to DR7 a pulled up connection to Z80 reset Ground And that's it The 5v is picked up from the Port 7 header. There is the posibility of accessing other port 7 signals, or the...

This structure means that USB support can, in principle, be implemented by replacing the cog 1 code by USB code which similarly queues key press and release events in the FIFO buffer. Could the theoretical USB code go in say cog 4, so that either type keyboard could be used depending which is plugg...

It's actually possible to get ATX size prototyping boards. Which means its possible to build something a bit like This.... mtx-ATX.jpg That's an old picture, the IDE and full MTX style keyboard are now working, instead of relying on the plug in card. However the long term plan is to add a PS2 (or US...

How often these days do we hear of MTXs with keyboard problems, repeating keys, "sticky" keys, plain dead keys ? From the inventive mind of Bill Brending, here's the solution. Use a PS2 keyboard instead! Bill's idea is to use a Propeller to provide an interface between the serial PS2 proto...

Further testing done on the video memory. The video ran is pushed harder that the main ram. It's shared between the VDG and the CPU with the VDG being forced off when the CPU wants to access it. The Atom's OS takes care to avoid contention by waiting for the vertical blank to write to the screen, wh...

An Update. Lez has been kind enough to send (via Dave) some different speed CPUs and other parts for testing. Test 1 was to replace all the AHC logic parts with the more widely available and usually cheaper HC, at that point the Intersil 82C55 PPI that controls the keyboard and VDG refused to take a...

Merry Christmas to everyone.

(mmmmm mince pies!)

Looking a the bookshelf, the most worn book there is my copy of Zaks' book "Programming the Z80" Which seems to be available at Archive.org https://archive.org/details/Programming_the_Z-80_2nd_Edition_1980_Rodnay_Zaks The MTX manuals themselves have good info on the VDP, sound chip etc. Th...

74AHC is pretty quick 9ns for the 08 and 11.5 for the 138. The real holdup is the time it takes the VDG to release the address bus to the video memory. Maybe if I were doing a re-design I'd use dual port memory there. Vram access time would them be the same as the rom. And allow room to run a couple...

The 65C02 is a relatively new one from WDC, I think their earlier versions were -6 or -8 and may be too slow for 6mhz use - see the math at the end ! The 6847 you sent via Dave happens to be a Motorola MC6847 part, though any of the other manufacturer's versions should operate the same. The 82C55 is...