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Old 12th Oct 2016, 3:42 am   #36
Karen O
Rest in Peace
Join Date: Jul 2011
Location: Bridgnorth, Shropshire, UK.
Posts: 787
Default Re: The Sinclair / Science of Cambridge MK14

There's no RAMIO. It's a close emulation but there are differences: address arithmetic DOES carry over into the top 4 bits and the memory map is not absolutely identical. Also, my emulation runs at 4MHz - the Mk14 was fitted with a colour crystal. The flags, sense and serial IO pins are there if you use the right PIC (PIC16F877). The emulation is accurate for code running in RAM but runs slower for ROM. This might affect cassette routines in ROM, though serial download (intel Hex) is included and avoids the need for cassettes.

There's also a bug in the original source. SC/MP jumps do not partake of extension register offsets but that's not clear in the datasheet. This lead to the 'JMP 80' bug. It should jump -128 bytes but instead jumps by an offset derived from the EXT register. Amazingly, that went undetected for some while. I ran NIBL Basic successfully with that bug! It was only discovered when someone wanted to use an earlier version of the SCIOS monitor. I'll send corrected files if you ever make one of my emulators.

There's a bug also in the original code which stops flag IO from working. I've corrected that too.

I recently made another of my emulators (see photo). It's in honour of the Apollo guidance computer - the DSKY (display/keyboard). It includes flag IO on a 9 way 'D' connector.
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