JR-IDE LBA Too Old

Hardware questions and modifications

Re: JR-IDE LBA Too Old

Postby Hargle » Mon Jun 17, 2019 5:55 am

Have you tried booting to your DOS floppy and typing "fdisk /mbr"?
This is typically the fix for drives that work when the machine has been booted via floppy, but will not boot from C:.

disclaimer: I am not 100% sure that command is supported in dos 3.3. It definitely works in DOS 5.0 which is a better choice for a PCjr with a hard drive anyway.
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Re: JR-IDE LBA Too Old

Postby Roscoe » Mon Jun 17, 2019 7:38 am

I seem to remember reading about the "fdisk /mbr" command somewhere in this forum before. Looking at some on-line references, it seems like the switch appeared at DOS 5.

I can't remember if I tried that command with DOS 3.3 or not. I think I did and got an error message and that's why I was going to try again with DOS 5.

If it seems like I don't remember much, I did this all late (very late) the evening I got the adapter to try it out. One should really not operate old computers when over tired.
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Re: JR-IDE LBA Too Old

Postby Roscoe » Mon Jun 17, 2019 11:35 pm

I got it to boot off the SD card. I finally put all the clues together.

The SD Card I had has a deficient MBR. In fact, it is all zeros (no executable code), with the exception of the partition table. So, there is nothing to start the boot process.

However, because there is a MBR present, FDISK will not replace it.

I used a linux machine to write zeros over the MBR on the SD card. Then started over with FDISK on the PCjr and since there was no MBR present, FDISK installed the correct one. FORMAT C: /S and I have a bootable SD card. Of course, this will delete all data on the SD card, so backup first.

If it is worth while, I can write this up in detail later (in another thread perhaps).

Of course, hargle's suggestion to use fdisk /mbr is easier. But if you are not running DOS 5, this is a way around the issue.
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Re: JR-IDE LBA Too Old

Postby Hargle » Tue Jun 18, 2019 6:21 am

Hurray! Glad you got it working. You've joined the club!
One could do the wiping of the SD card right there on the PCjr with the help of debug.

debug
a
mov ax, 309
mov cx, 1
mov dx, 80
int 13
int 20

g

then reboot.

As a terrible teenager, I used to do this to the Tandy machines on display at radio shack.
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Re: JR-IDE LBA Too Old

Postby Roscoe » Wed Jun 19, 2019 7:13 am

As I was booting a full blown modern operating system to write zeros to a single sector of a drive, I was thinking "There must be a way to do this with debug." Now I know!
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Re: JR-IDE LBA Too Old

Postby bagelswitch » Tue Jul 02, 2019 10:08 pm

kotto7877 wrote:

This is exactly the SD to IDE adapter that I bought, as well. This is the only listing on Amazon that gave a hint that it might be compatible by the description that says this:

Attention: Some of the mother board required to enable LBA mode and disable DMA transfer mode.

I just couldn't shake the feeling that maybe I needed to patch something (given comments in the past about having to patch certain versions of DOS to work on the jr). Since you have exactly the same problem as I have, it's probably not the case.

I am having fun with this, but I don't want to remain dependent on the floppy drive. I still have nightmares of floppies going bad at the worst times. On the upside, I've ordered a Gotek floppy emulator, which should make things substantially better for me in a couple of weeks or so. I have been away from retro computing for so long that I didn't even know about this Gotek floppy emulator until recently.

I had the same thoughts as you regarding the use of an SD card: easiest way to copy files to/from modern computers.


I recently starting using a gotek emulator as the boot device on my PCJr and it works great using the HxC firmware(https://hxc2001.com/store/index.html), but a tip - while .img and .ima image files can be placed directly on the USB media w/ the Gotek, the disk type for a given image won't be properly reported to the floppy controller when changing images, or at all, and you'll find that only 180/320kb images work.

If you instead use the HxCFloppyEmulator software to convert images to the hfe format, all disk types supported by the controller will work and you can switch between a mix of types (eg. boot a 180k DOS 2.1 image, then run software from a 720k DSDD image) on the fly with no problems.
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Re: JR-IDE LBA Too Old

Postby kotto7877 » Thu Jul 11, 2019 4:37 pm

bagelswitch wrote:
kotto7877 wrote:

This is exactly the SD to IDE adapter that I bought, as well. This is the only listing on Amazon that gave a hint that it might be compatible by the description that says this:

Attention: Some of the mother board required to enable LBA mode and disable DMA transfer mode.

I just couldn't shake the feeling that maybe I needed to patch something (given comments in the past about having to patch certain versions of DOS to work on the jr). Since you have exactly the same problem as I have, it's probably not the case.

I am having fun with this, but I don't want to remain dependent on the floppy drive. I still have nightmares of floppies going bad at the worst times. On the upside, I've ordered a Gotek floppy emulator, which should make things substantially better for me in a couple of weeks or so. I have been away from retro computing for so long that I didn't even know about this Gotek floppy emulator until recently.

I had the same thoughts as you regarding the use of an SD card: easiest way to copy files to/from modern computers.


I recently starting using a gotek emulator as the boot device on my PCJr and it works great using the HxC firmware(https://hxc2001.com/store/index.html), but a tip - while .img and .ima image files can be placed directly on the USB media w/ the Gotek, the disk type for a given image won't be properly reported to the floppy controller when changing images, or at all, and you'll find that only 180/320kb images work.

If you instead use the HxCFloppyEmulator software to convert images to the hfe format, all disk types supported by the controller will work and you can switch between a mix of types (eg. boot a 180k DOS 2.1 image, then run software from a 720k DSDD image) on the fly with no problems.


Thank you for the info; I just got my Gotek recently but haven't switched it to the HxC firmware yet. I've soldered pin headers onto the device for programming it, but that's as far as I've gotten so far. Too little free time and too many other things to work out... I do want to get this up and running soon, especially given the fact that I'm still without the ability to boot from a DOM or SD card.
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Re: JR-IDE LBA Too Old

Postby bagelswitch » Sat Jul 13, 2019 7:59 am

bagelswitch wrote:If you instead use the HxCFloppyEmulator software to convert images to the hfe format, all disk types supported by the controller will work and you can switch between a mix of types (eg. boot a 180k DOS 2.1 image, then run software from a 720k DSDD image) on the fly with no problems.


Just realized my example is a bad example, since of course you won't be able to read a 720k disk under DOS 2.1, but the general concept is accurate :)
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