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

Test rom updated to build 245. the Ram test has been expanded to stop on read failure with a brief diagnostic as shown on this screen dump from the emulator. Since the emulator never actually fails the read back, this is actually fake, :D but it looks better than a photo of my 1980's green screen mo...

If you're going with a high pin count CPLD, then that means working at 3.3v instead of 5v. Rather than invest in a mass of level shifting to accommodate a Z80, the low power version of the Z180 might be an easier fit. The Z8S180 has 20mhz 3.3v version. For an idea of resource cost, I've VHDL code fo...

If you're building a system that can't use PS2 or USB, then the cost of the keyboard components is possibly the biggest outlay. Buying from Mouser in packs of 100, a 12mm key and keycap works out at 60.6p each. With anywhere between 40 (ZX81, Spectrum) and 80 (MTX/MSX/SAM) in a home brew, that can b...

The memory test could be re-written to stop at a failed read back, and then print something along the lines of "Value read :XX value expected :XX". at which point the test would have to stop. I don't think there's enough registers to do much more than that. Re-starting and only halting onc...

Crazyboss wrote: ↑20 May 2019 15:32 If its Cambridge, I looks like there is an airport nearby, but its seems like its closed, at least its not possible to fly there from Copenhagen

Try flights to and from London Stanstead - that's got a direct train to Cambridge, takes about half an hour according to the time table.

I only mentioned the TIP as that was a problem with one of my MTXs. I spent 2 weeks chasing a "timing problem" of random crashing and inability to run programs for any length of time, which turned out to be nothing to do with the timing. Anyway, if the big 10R resistor R62 next to rom B is...

Silly question, did you replace the TIP2955 in the power regulation section ?

(20 pages of thread is a lot to re-read, so I'll just ask instead )

I've used the 10mhz CMOS Z80 (Z84C0010PEG) in my MTX's for years, with no issues. In fact we found out it works better with the CFX2 than the NMOS version. The only reason one of them has the NMOS chip back in it is for testing. As Dave says we've found a lot of fakes marked up as the 20mhz part (Z8...

One advantage of de-soldering rather than clipping legs is, if the 32k onboard is made up of the 3732H part, you potentially have replacements for the video ram. The trick for replacing a 4116 with a 4164 ties A7 high to reduce the chip to 16k x1 which would in theory work on the high bank 32k chips...

Something to consider, the RUN type games usually load and run at #8100. REV.RUN is 14k in size so fits entirely into the paged memory area between 8000 and BFFF STAR.RUN is 18k in size so overflows into the unpaged memory at C000 onwards CPM has all of it's drivers in the top 4k of the unpaged area...