PCW8256 -> PCW8512, getting ready for Gotek/FDD work, what do I need to know!

[erikarn]

hi! I've ... found a mint PCW8256 here in the US that's somehow working at 50Hz / 256 line mode. I've ordered a gotek to install in it, and maybe (!) a second 180k drive because I do already have a CPC6128 and CPC6128+ with working drives and a HXC to copy images around with. I've updated the RAM from PCW8256 to 512k.

I've done some digging in preparation for this and I'd just like to make sure I've got a good summary of what's going on with this hardware, CP/M versions and gotek hackery.

From what i've found so far:

* If I want to use a gotek, is the CPM/3 1.5 I have is fine as drive A: ? Will it detect it as a 180k drive and use 180k images ok?
* The boot ROM makes assumptions about A: being 180k on the 8256?
* the earlier CP/M 3 versions don't probe the kind of drive attached to B:, so it assumes it's a 720k DD/2H drive?
* If I want FID support, I want at least 1.07H ? I've been working on disassembling the CP/M 1.15 .EMT file into its component pieces and disassmbling the non-CP/M bits, partly for FID and partly for fun.
* If I try booting 1.15, then I'd have to either patch CP/M or fix the Gotek to correctly assert the motor line, so CP/M knows what's up?
* I need to pay attention to the drive cabling (like for the 6128/plus) and also the reverse power connector stuff?
* People have mentioned 180, 720 FIDs for A: and B:, where are those files located?

Thanks!

Image for post tax!

-adrian

[GeoffB17]

Hello,

Most of your notes are OK, but:

Note that the PCW 8256 does NOT have any 'Boot Rom'.   There is however a boot sector on the boot disk which contains code, and this code certainly DOES assume that the boot disk is a single sided 40t disk.  You could of course use a boot image for a 9512 with an appropriate system.

Yes, system 1.07H does allow the use of FID drivers, but I suspect that this does NOT include the drivers for swapping the disk parameters, I suspect that this is still fixed into the systems.  To do this, you would need a later system that COULD allow such a change, with the FID files to enable a 720k drive as A: or a 170k drive as B:, but this would cause the other problem you mention regarding the use of an unmodified Gotek.

Geoff

[erikarn]

Hi, thanks for replying!

Yeah, I know about the boot rom versus "boot rom". That's why i asked about whether it's assuming a 180k disk, or whether that matters (ie, it just looks like it's slurping the first chunk of blocks from the disk and running it, so it likely doesn't care too much yet about the track/head/sector layout, as long as it's MFM and not FM?)

If I wanted to boot a 720k image on an 8256, then I'd have to do .. what?

[GeoffB17]

Yes, it does matter.   It's the first sector of the disk ONLY, and the code there isn't very clever, and no CP/M is loaded yet to help.  It looks for the .EMS file on the disk, and reads it, and it assumes SS and 40t.

The similar code on a 9512 boot disk will assume DS and 80t, so that might be OK.

But for an 8256, once the stsrem has booted, then there may be conflicts between what the system expects (requires) and what there really is, this is when you'll need the FID files to resolve the (possible) conflict.

Geoff

[erikarn]

Right, I've looked at the printer-microcontroller supplied power-on loader dump from john and others, and yeah it sucked in the first sector as an MFM read from head 0 and jumped into it. I've actually gone and disassembled the boot code from a 180k 8256 image that I whacked the 1.15 EMT file into in joyce so I can see the boot flow there.

I guess if I want to do something on a 720k image w/ CP/M 1.15 then I'll have to hand assemble that too from an existing 720k CP/M boot disk image (and I'll likely disassmble the 720k bootloader too. :-)

Thanks!

[GeoffB17]

Hello,

Just wondering.

As far as I know, if you use the Gotek as A:, and boot from A: type images, then you should be OK, if you use the i.07H system (which avoid the pause/disk error problems with the Gotek if you don't want to modify it).

There WOULD be a problem even READING from a B: type disk in A:.   Some time ago I needed to use my system with a 5.25" drive, and boot from that.  I wsa able to manage that using a SS format, so the drive/disk look like a normal 3" disk.   I had the drive's usual DS (360k) disks, I had to use an 1.2 system ('patched' as per John Elliott's instructions) to get the system to read the DS disks).  But you cannot do that because of the Gotek problem?

Do you really NEED to be able to BOOT from a B: type image in A: ? - THIS is leading to problems.   I would guess that ALL the software you likely need to access will be on A: disks or images.

You should be able to use the B: type disks in B: OK, 3" disks or Gotek/images.   The B: drive will (normally) let you READ A: type disks in the B: drive, for copying files etc.  I'd assume that this will be the same with Gotek/images.

Are there specific reasons why you want to go beyond these parameters?

Geoff

I'm assuming you use a B: type 3" drive as B:

[erikarn]

oh I'm just trying to get all my ducks in a row in case I /do/ want to do something odd.

I was hoping to use the gotek for A:, and then put the 180k drive in as a B:, so I can use actual drive media for things like archival and some occasional use.

What do you mean by a "B: type disk" ? If I wanted eg a 720k A: but a 180k B: , things may be problematic?

[GeoffB17]

A B: type disk is the 720k one (CF2DD).

If you try to use the CF2 drive as B: this MIGHT cause some problems (just not sure) but as the 8512 (standard) can READ the A: disks anyway (as standard) you might be OK - but you may have problems if you want to WRITE to the A: type disk in B:.

The PCW uses the first 16 bytes of the boot sector to define the disk (format) type, and I assume that is the data that will determin any errors thrown.  So my DSDD drive (5.25") referred to above worked fine because the disks I was using were formatted as SSDD so they were marked as such on each disk so the PCW was happy.  As I understand it, it's the disk (or the image) that causes the problems rather than the drive (apart from the power problem mentioned).

Geoff

[erikarn]

Ah good to know!

how'd you mount your 5.25" drive btw?

[GeoffB17]

The 5.25" drive is external, it's from Box, got it 1986 soon after I got the PCW.   Much later I altered the connecting cable so it was outside, and I could swap B: between the 5.25" drive and a 3.5" drive, but I mostly use the 5.25 as I prefer those disks.   The space not so important, as I've got one of the uIDE drives (virtual HDs).

Geoff

[erikarn]

Ah did they just feed a cable through the case somehow?

[GeoffB17]

When I originally got it, the cable quite neatly came through the existing slot where the printer connector also comes through, although this was fairly limiting as to where the drive would sit.   When, many years later, I got the 3.5" drive set up as an alternative for the same connector, I needed more flexibility, so I made a new slot on the side.  Not as tidy, but not too visible.   Ok for me.   So I can grip enough cable to get at the connector (which was inside before) and unplug one drive, and re-plug another.

Geoff

[GeoffB17]

You asked before about the drivers to adjust for the drive settings.  These may actually be .FIB files.

The FID files are to extend the system, while the FIB files merely change some existing settings within the system (in the case involved, to change some drive settings).

I've had a look through various drives here (not everything yet) and I see that I have a B180.FIB, which will adjust the system for an A: drive as B:.   But this will prob work ONLY with the later systems that have the settings soft coded in the system, the older systems will not?  I've also found an A35.FIB, which is for putting a 3.5" drive as A: (the 3.5" disk is in effect the same format as the B: 3") but I think this driver is to do with speed settings which may not be relevant to what you want to do.

I don't think I've seen an A730.FIB, and I'm not sure any such would help you.

I'll keep looking.

Geoff

[cj7hawk]

I haven't tried booting an image in a 8xxx from a Gotek yet, but from booting the 9xxx from 8xxx images ( which it does do ) you need to change the checksum of the boot sector so it knows it's a 8xxx boot image.

As long as the checksum of the boot sector is correct, it will boot from whatever the disk throws at it from Track 0.

Booting successfully may be another matter, and you need the correct OS elements, but that was how I converted 8xxx games to run on the 9xxx on Gotek images - I just modified the boot sector of the image so that the checksum changed from 8xxx boot image to 9xxx boot image.

[JohnElliott]

As far as CP/M is concerned, an 8xxx will boot from a 9xxx system file or vice versa. The built-in printer won't be usable and a few keyboard keys will be different, but everything else ought to work.