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5150 issues

U

Unknown_K

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Joined
Sep 11, 2003
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I dug an old IBM CGA video card out of my junk box (got one with no bracket and the CGA connector missing figuring it was junk it sat in a box until I got cheap and soldered a 9 pin connector on it and found it works) and found out my unit works. Too bad IBM used a connector with long pins I have to hold the CGA monitor cable to the plug otherwise it falls off.

The jumpers are set up for 544K (OFF, OFF,OFF,OFF,ON is what the unit came with) but since I can't get it to boot from a floppy (homemade DOS 3.3 disk works on my XT clone with HH drives) it dumps me to BASIC. The unit is the 16-64K board with full RAM, has a 64K RAM card and a Monte Carlo multi function RAM card full of RAM (no idea about how much RAM that would be). It dumps me in basic C1.00 62940 bytes free, does the machine only think I have 64K installed or is that because of the BASIC ROM version? I don't get any beeps for RAM mismatch but I also don't see a RAM countdown on the screen like you get in later PCs to know how much RAM is installed.
 
The 5150 had no ram test count on the screen, so that part is normal. My first suspicion about the floppy boot problem is that switch one, on switch block 1 (near the center of the motherboard) is turned on. That will disable disk bootup and send it straight to Basic.
 
The switch is in the OFF position, and the drive is active like the machine is trying to boot from it before it dumps me to BASIC.
 
Unknown_K said:
It dumps me in basic C1.00 62940 bytes free, does the machine only think I have 64K installed or is that because of the BASIC ROM version?
Click to expand...
The 5150's cassette BASIC uses 64 KB of RAM.
If you want to see how much 'conventional' RAM that the POST found at start-up, then type in the following two lines in BASIC:

def seg = &h40
print peek(20)*256 + peek(19)
 
modem7 said:
The 5150's cassette BASIC uses 64 KB of RAM.
If you want to see how much 'conventional' RAM that the POST found at start-up, then type in the following two lines in BASIC:

def seg = &h40
print peek(20)*256 + peek(19)
Click to expand...

I get 544. Is that the actual ram or just what I have the jumpers set for. My understanding is you can't get 640K on a PC correct?
 
modem7 said:
Which BIOS do you have on that 16KB-64KB motherboard?

Do you have another 360K drive that you can try?
Click to expand...
I assume since the ROMS are IBM stamped and I have C1.00 BASIC it is the original IBM ROMs. I do have another 360K FH drive here somewhere, but I will try making a DOS disk using my XT clone first (everything else uses a 1.2Mb HD and the track width is smaller).
 
Unknown_K said:
I get 544. Is that the actual ram or just what I have the jumpers set for.
Click to expand...
Because you don't see a 201 error, either:
1. You could have 544K fitted and SW2 switches set for 544K.
2. You could have more than 544K fitted, but SW2 switches set for 544K.

Unknown_K said:
My understanding is you can't get 640K on a PC correct?
Click to expand...
The first and second BIOS revision has a 544K limit.
The third (and final) revision has a 640K limit.

Different switch setting apply to SW2 dependent on BIOS revision.

Unknown_K said:
I assume since the ROMS are IBM stamped and I have C1.00 BASIC it is the original IBM ROMs
Click to expand...
The C1.00 BASIC indicates that the BASIC ROMs, chips U29 to U32, are the original ones.
The BIOS resides in chip U33 and may have been upgraded.

To see which BIOS you have:
1. Go to http://www.minuszerodegrees.net/index.htm
2. Select link 'IBM 5150 - BIOS Revisions'
 
All the BIOS chips look original, havn't written down any numbers yet (cards obscure the view I think).
 
Thanks very much.

The program I sent by Email is to check simple ROM checksum program on BASIC.

Your BASIC C1.00 must be correct one and BIOS version is just identical Revision 2 (10/19/81)

(You can check BIOS date by using BASIC)

DEF SEG=&HF000:FOR I=&HFFF5 TO &HFFFC:pRINT CHR$(PEEK(I));:NEXT

But I wonder what ROM is from 0000-5FFF (Segment F000)

Checksum from 0000-5FFF has different value I expected.

Can you dump 0000-5FFF by DEBUG.EXE?


A:\VERIFY ON

A:\>DEBUG

-N 6000.BIN

-R BX
BX 0000
:0000
-R CX
CX 0000
:6000

-M F000:0 6000 0100

-W 0100
Writing 6000 bytes

-Q
 
Last edited:
Yes.

Original BIOS (04/24/81) is very hard to find.
But it was already dumped from any kind people.
 
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