Sunday, February 17, 2019

Using EGA and VGA video cards in IBM 5150 PC, 5155 Portable, and 5160 PC/XT Machines

I first ran into video card issues debugging the IBM 5155 Portable computer. Besides no video it beeped one long, two short on startup. I did a lot of video card switch and jumper gymnastics to try to get that straight when I should have done more digging online. Two switches on the motherboard would have probably done the trick.

So I have compiled a short primer on using EGA and VGA displays on these machines. Most of the info is from various pages of the excellent site but in multiple places. Hopefully having this in one place helps others.

Do note: there are alot of caveats in this and not all cards will work in all computers. One reason I don't make a compatibility table (yet) is others have done so and it gets expensive testing.

Motherboard switch settings for EGA and VGA (BIOS-containing) Video Cards
Version 1.00

IBM 5150 PC

·       The IBM 5150's motherboard must have the third BIOS revision, 10/27/82, for EGA/VGA
o   The ROM has the IBM part number of "1501476" printed on it.
o   On the 5150 motherboard, the ROM in socket U33 contains the BIOS.
o   Due to bugs, this BIOS requires that all 4 banks of motherboard RAM be populated.
·       The two video switches on SW1 (shown below) must be set for:  5=ON, 6=ON

·       Of SW1 and SW2, SW1 is the switch block closest to the center of the motherboard.
These settings apply to both the '16KB-64KB' and '64KB-256KB' versions of the 5150 motherboard.

·       If your IBM 5150 contains an XT-class hard disk controller, then be aware that some VGA cards may have a resource conflict with it.

·       Known working VGA card lists: minuszerodegrees, vcf

IBM 5155 Portable PC

The IBM 5155 contains an early version of the IBM 5160 motherboard.

So, see below to see the 5160 motherboard switch settings, noting that the two switches for video card type are normally set to CGA (because an IBM CGA card is the card supplied by IBM in the 5155).

IBM 5160 PC/XT

·       The two video switches on SW1 (shown above) must be set for:  5=ON, 6=ON

·       Do not place the card in expansion slot 8 (the slot nearest the CPU) unless the card specifically supports slot 8.  Cards that are slot 8 compatible usually have a 'slot 8' jumper.

·       If your IBM 5160 contains an XT-class hard disk controller, then be aware that some VGA cards may have an address space resource conflict with it.

·       Known working VGA card lists: minuszerodegrees, vcf

Boot Error Beep Codes for Video

1 long and 2 short beeps                    Video (Mono/CGA display circuitry) issue
1 long and 3 short beeps.                   Video (EGA) display circuitry
1 beep, blank or incorrect display       Video display circuitry.

·       Make sure the SW1 switches are in the correct 5=ON 6=ON position (above)

·       Ensure there are no conflicts between VGA BIOS/addresses and other cards

·       Be sure the video card configuration switches are correct (this could be hard without documentation)

Suitable VGA cards

You must not assume that because a particular VGA card works in an IBM 5160 (IBM XT) that the same card will also work in an IBM 5150.
The documentation for some 16-bit VGA cards indicates that they work in an 8-bit expansion slot.  You should not expect that to mean all 8-bit slots.  Many such cards are intended only for an 8-bit slot within an AT-class computer, and will not work in an IBM 5150.  The maker's documentation for the card will indicate whether the card will work in an IBM 5150.
Some people have discovered that certain 8-bit compatible 16-bit VGA cards can be made to work in a 5150/5160 if the 8088 CPU on the motherboard is upgraded to a V20 CPU. This may not work, though.

VGA card configuration

Some VGA cards have configuration switches and/or jumpers.  An example is here.  Refer to the card's documentation to ensure that those switches/jumpers are set appropriately.  For the switches, do not confuse the off position with the on position.
16-bit VGA cards that are known to work in an IBM 5150 PC usually (not always) need to be manually configured to run in 8-bit mode.  Refer to the card's documentation, because configuration is done differently on different cards.

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