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Re: Changes to Z80MC?

 

Hi,

This is an idea for a small change to the Z80MC firmware.? I did it on mine a while ago and it helped me at the time.

I had formatted my SDCARD?from windows, and had a hard time booting off of it.? I can't remember which windows, but it was probably Windows 10.
(Has anyone else had this problem?)

It turned out that my FAT16 format was of type SD_PART_TYPE = 0Eh.
This is a slightly?modern variant of FAT16, but I think it works fine with the rest of the Z80MC disk routines.

The current firmware allows SD_PART_TYPE?4 or 6, and disallows type 86h:

2306 ?32 16FF ? ? ? ? ? LD (SD_PART_TYPE), A
2309 ?FE 04 ? ? ? ? ? ? CP 4
230B ?28 09 ? ? ? ? ? ? JR ? Z, INITFAT_PGOOD
230D ?FE 06 ? ? ? ? ? ? CP 6
230F ?28 05 ? ? ? ? ? ? JR ? Z, INITFAT_PGOOD
2311 ?FE 86 ? ? ? ? ? ? CP 86h
2313 ?C2 6624 ? ? ? ? ? JP ?NZ, INITFAT_FAIL

I added one more case for 0Eh, and that allowed me to boot off of the card.

If this firmware change is legit/correct, and?it makes it easier for Windows users, perhaps it would be good to go in with the next firmware update.

You can read more about this FAT16 version here:

But I have excerpted the relevant part here:
Prior to 1995, versions of DOS accessed the disk via??addressing only. When?(MS-DOS 7.0) introduced??disk access, partitions could start being physically located outside the first c. 8?GB of this disk and thereby out of the reach of the traditional CHS addressing scheme. Partitions partially or fully located beyond the CHS barrier therefore had to be hidden from non-LBA-enabled operating systems by using the new partition type??in the partition table instead. FAT16 partitions using this partition type are also named?FAT16X.?The only difference, compared to previous FAT16 partitions, is the fact that some CHS-related geometry entries in the BPB record, namely the number of sectors per track and the number of heads, may contain no or misleading values and should not be used.

-Frank


On Sun, Apr 27, 2025, 2:02?PM Lee Hart via <leeahart=[email protected]> wrote:

Thanks for your suggestions, Kerem.

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1. I am resolving the S8 problem by changing Q3 from an FJN3305 (internal 4.7k) to an FJN3304 (internal 47k). If anyone wants an FNJ3304, email me and I can send you one for free.

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2. The piezo's beeps are indeed pretty weak. There simply was no room for anything better! That's why it's sitting on top of the ICs. However, a "naked" piezo doesn't make much noise. Some kind of speaker enclosure is needed to amplify the tiny movements of the disk into larger air movements. This usually take the form of a coin-shaped lid with a small hole in the center. For example, the lid of a pill bottle about the same diameter as the piezo disk, with a 1/8" hole in the center. That helps a lot (but adds height so it won't fit in an Altoids tin).

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A bigger or better speaker would be great. But where would I put it?

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3. I standardized on the white Molex KK series connectors because they are available with gold contacts, and have good spring pressure to make reliable?connections. The black "Arduino" style connectors that have become popular are cheap, but not very reliable. If you pull out a pin and look at the actual contact surfaces, you'll see that they are rough, and only tin plated or gold-flashed which wears off quickly, and there is no spring pressure to maintain contact pressure.

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But the Arduino-style connectors certainly make assembly easier. They are actually needed for the Z80-SIO card because the Molex KK connector would hit the 5v regulator.

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I'm thinking about removing the 5v regulator, as I doubt anyone powers their Z80MC with anything other than a 5v supply. This makes room for Molex connectors at all P1 and P2 locations on the CPU card. It also makes room to include the P4 power/serial connector on all CPU cards.

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4. Supporting NVRAM on the Z80-SIO card is a great idea! I'm not working on it at the moment, but will add it to my list of "things to do" when I order more PCBs. You could use a NVARM with built-in battery now; but they are expensive. Most likely, I'd use VIN (JP2 pin 20) to connect an external battery.

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5. Yes, there is room in the ROM to include some self-test capability. Another project! :-)

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Anyone have any other ideas?

?

Lee

--

Excellence does not require perfection. -- Henry James

But it *does* require attention to detail! -- Lee Hart

--

Lee A. Hart

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