Useful Tips & Tricks

This page contains some useful tips and tricks for MCA-based PS/2 machines.

How to get out MCA-card IDs from IBM BASICA
How to determine / change FDD-type from BASIC


How to get out MCA-card IDs from IBM BASICA

Assumed you have a machine which refuses to boot from disk as well as from harddisk and you land in the IBM ROM-BASIC after pressing the [F1] function key.
No problem to get out the IDs of the installed adapters.
If you'd already downloaded QBMCA or the MCA.DAT-file, just print out MCA.DAT.

Warning: MCA.DAT is a rather long file (>71KB) !

Then type the following BASIC program:

10 cls
20 for q=15 to 8 step -1
30 out(&H96),q
40 print q-7;": ";hex$(inp(&h101));"-";hex$(inp(&h100))
50 next q

Press [F2] to RUN the program.
The output will be a list starting with 8 and the Card-ID for the Slot #8 (uppermost in Mod. 80). On machines with only 3 or 4 slots only the lower are valid, all others will show FFFF. It might look like that:

8: 8E-FE (= IBM SCSI without cache)
7: F-1F  (= Adaptec AHA-1640 SCSI)
6: E0-1 (= IBM 16/4 Mb/s Token Ring)
5: FF-FF
4: 8F-DA (= IBM XGA-2 Video)
3: FF-FF
2: FF-FF
1: FC-FF (= IBM 2-8MB 386 Memory)

If the ID is i.e. 8E-FE the MCA.DAT-listing tells you it is the IBM SCSI-Adapter without cache. If the ID is for example F-1F the trailing 0 for the first half is missing and it is 0F1F. If the ID is E0-1 the trailing 0 for the last half is missing - look under E001. If the ID is FFFF the slot is empty.

How to determine / change FDD-type from BASIC

Assumed you have a machine which refuses to boot from floppy disk and probably from harddisk as well and you land in the IBM ROM-BASIC after pressing the [F1] function key.
Maybe the type of floppy disk has got lost in the Configuration.
To test this type the following BASIC lines:

OUT(&H70),&H10
PRINT HEX$(INP(&H71))

The output should be 40, if there is only a drive A: installed and it is a 1.44MB-drive.
The first digit is the drive-type for A: (first FDD), the second digit is the drive-type for B: (second FDD).

Possible numbers are:

0 = not installed
1 = 360KB / 5.25 Inch
2 = 1.2MB / 5.25 Inch
3 = 720KB / 3.5 Inch
4 = 1.44MB / 3.5 Inch
6 = 2.88MB / 3.5 Inch
8 = Tape or reserved

You might change the type of drive with simply typing:

OUT(&h70),&H10
OUT(&H71),&H40

But this might not help much if you landed into IBM ROM-BASIC. There is no way out from it into an operating system, because the operating system has not loaded. And -of course- you cannot access the FDD from out of ROM-BASIC.
After a reboot with [CTRL]+[ALT]+[DEL] the CMOS value might have got lost again. But it is worth trying ... in most cases the FDD accepts at least 720K-disks to boot from.


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