MTXplus+ Running CP/M
Posted: 17 May 2015 19:56
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Here's a screen shot of my MTXplus+ prototype running CPM.
The implementation leans heavily on Andy's code for the Rememorizor. The system monitor, keyboard, ram disc and all the higher level SD card software is ported over from there unchanged. The low level card access for the CF card fitted on the prototype, replacing the SD card routines, are the same ones we've been using for FAT32 read only access.
Video access had to be written from scratch, as the system is using the Yamaha V9958 in text mode 2 and not a dedicated 80 column card.
This means that when MTX.COM or one of the games is run, or the system is booted bypassing CPM start-up, there's no requirement to change monitors as all output goes through the same VDP.
The downside of using text 2 mode, is the lack of character attributes, output is mono only.
Although the CPU board has a 20mhz Z80 fitted, the system is currently limited to 11mhz while a hardware solution to a problem with the timing of the connection between the CPU and VDP is sought.
However, at 11mhz CPM is surprisingly quick, and as you would expect 2-3 times as fast as the MTX/Rememorizor combination. Though I imagine somewhat slower than a 25mhz Rememotech.
