> having one 8bit that didnt work in a 16

If it worked on an 8-bit slot on the same mainboard then your port was dirty or broken. Otherwise, 8-bit VGA cards tend to be rather old and thus can have BIOSes with speed bugs.

> will a vlb card work in an isa slot?

There's no point even if it does work

The 8 bit card that didnt work was some kind of 3d glasses card, I recall getting a message that it couldnt work in that slot or that kind of slot or some such. The motherboard was a PA2013 board ie socket 7, so quite a bit newer. I no longer have the card [threw it away after that, and the glasses had leaked anyway].

Regarding VLB/ISA, I was thinking of whether a VLB board would work in a board that only has ISA slots, rather than using a VLB board in an ISA slot when you have a VLB available.

The pins of all ISA slots, no matter if an 8-bit slot or the 8-bit portion of a 16-bit slot, are connected to the same signals. There is no way for software to know.
There may have been ressource conflicts with your glasses card.

The VLB thing is still pointless imo. If it does work it will be dog slow, its end may bend somewhere where you wouldn't want to have it. In all the years I tinkered with computer stuff I never felt the need to try this out.

ratfink wrote:

will a vlb card work in an isa slot?

Unless a VLB card is designed to work with a 16-bit ISA slot, it will not work. If you would like to experiment, you can try out those VLB-based I/O controllers (IDE/Floppy/Serial/Parallel combo) on a ISA slot.

ok thanks, in view of what you both say i will not bother with this train of thought any further. twas prompted by some ebay items and the urge to build something i dont need anyway 🤣

*Rise from your grave!!!*

In regards to VLB video cards working in ISA slots, some do. For instance the Power! Cards that have weitek chips also have a seperate VGA chip on the card. And only seem to use the VLB functionality if you load drivers or run Windows. Certain Cirrus Logic VLB cards seem to be 16-bit as well and will run in a ISA slot. I only know this because a friend was recently testing a 386/486 motherboard with a VLB slot. Online sources claimed the slot was non functional but after testing several VLB cards most would not work but a few did work. Our guess was that the ISA part of the slot was functional and the extended VLB section was not, thus most cards didn't work.

One advantage of this is many Cirrus Logic VLB cards support 2MB of RAM while ISA counterparts tend to top out at 1MB (if im remembering correctly). Not that 2MB on a video card makes much difference in DOS.

And most VLB Multi-IO use the VL bus for one of the IDE interfaces only. So if you use it in an ISA slot you can still access the other devices on the card.

My pal mkarcher has a VL multi-IO controller that supplies an ECP paralell controller through an IO-chip that is connected via the 8-bit-ISA.
In his Turbo-XT the IDE part does not work of course, but the ECP paralell port does. And his external CDROM gains almost double speed performance.

There were IO cards that had optional VLB paddles you could tack on.

https://theretroweb.com/expansioncards/s/unkn … -super-i-o-card
https://theretroweb.com/expansioncards/s/gsi- … 21-1533-21-09-1

But VGA cards? Was not uncommon to see them leave outthe 16bit portion completely.

https://theretroweb.com/expansioncards/s/agatech-mvga-542x

They might work fine as long as you stick with real mode VGA BIOS calls. I find it hard to believe they would work with anything that tries to do go into 32 bit protected mode.

soviet conscript wrote on 2024-12-14, 02:02:

In regards to VLB video cards working in ISA slots, some do. For instance the Power! Cards that have weitek chips also have a seperate VGA chip on the card. And only seem to use the VLB functionality if you load drivers or run Windows.

As these cards combine two separate graphics solutions (one is typically an OAK or a Weitek 5186 chip, the other one the Power 9000) onto one card, every application that just uses the VGA-compatible part which is a plain old ISA VGA will work without VLB interaction, unless the card initialization during POST requires interacting with the Power 9000 chip.

soviet conscript wrote on 2024-12-14, 02:02:

Certain Cirrus Logic VLB cards seem to be 16-bit as well and will run in a ISA slot. I only know this because a friend was recently testing a 386/486 motherboard with a VLB slot. Online sources claimed the slot was non functional but after testing several VLB cards most would not work but a few did work. Our guess was that the ISA part of the slot was functional and the extended VLB section was not, thus most cards didn't work.

It is true that the whole Cirrus CL-GD542x series has a 16-bit host bus interface. It is furthermore true that these chips can be directly connected to an ISA bus and a 16-bit 386SX local bus. With a small amount of glue logic that multiplexes 32 bits down to 16 bits it can also be connected to the 386DX and 486 local bus. Nevertheless, the 542x chip can not be connected to the ISA bus and the VL bus at the same time. It makes no sense to implement mode switch logic that connectes the 542x chip to either the ISA or the VLB depending on which slot this card is inserted to, so I consider 542x VL cards running on 16 bit ISA a myth.

soviet conscript wrote on 2024-12-14, 02:02:

One advantage of this is many Cirrus Logic VLB cards support 2MB of RAM while ISA counterparts tend to top out at 1MB (if im remembering correctly). Not that 2MB on a video card makes much difference in DOS.

2MB on Cirrus cards only makes sense in certain special circumstances. There are already a lot of VOGONs thread educating about the uselessness of the 2MB upgrade on Cirrus 542x cards. Their main point is: As long as you don't use off-screen memory (for double-buffering, for containing sprites to be drawn, for caching fonts...), you don't need more memory than required for a single frame of video data. The memory bandwidth of the the CL-GD542x chip is so low that it can not display more than 1MB at any sensible refresh rate. Upgrading from 1MB to 2MB adds two modes. If I remember correctly, these are 1280x1024 256 colors @ 87Hz interlaced and 1024x768 65536 colors @ 87 Hz interlaced. Both of these modes provide sub-par quality on many CRTs and are incompatible with most LCDs.

As most consumers didn't have 2MB cards, there are very few if any VESA DOS games that use page flipping for double buffering if this would require more than 1MB of video RAM, even though the VESA BIOS Extensions did specify a way to access page flipping and hardware panning, if implemented on a card (most SVGA cards are capable of those features).

mkarcher wrote on 2024-12-14, 15:47:

As these cards combine two separate graphics solutions (one is typically an OAK or a Weitek 5186 chip, the other one the Power 9 […]
Show full quote

soviet conscript wrote on 2024-12-14, 02:02:

In regards to VLB video cards working in ISA slots, some do. For instance the Power! Cards that have weitek chips also have a seperate VGA chip on the card. And only seem to use the VLB functionality if you load drivers or run Windows.

As these cards combine two separate graphics solutions (one is typically an OAK or a Weitek 5186 chip, the other one the Power 9000) onto one card, every application that just uses the VGA-compatible part which is a plain old ISA VGA will work without VLB interaction, unless the card initialization during POST requires interacting with the Power 9000 chip.

soviet conscript wrote on 2024-12-14, 02:02:

Certain Cirrus Logic VLB cards seem to be 16-bit as well and will run in a ISA slot. I only know this because a friend was recently testing a 386/486 motherboard with a VLB slot. Online sources claimed the slot was non functional but after testing several VLB cards most would not work but a few did work. Our guess was that the ISA part of the slot was functional and the extended VLB section was not, thus most cards didn't work.

It is true that the whole Cirrus CL-GD542x series has a 16-bit host bus interface. It is furthermore true that these chips can be directly connected to an ISA bus and a 16-bit 386SX local bus. With a small amount of glue logic that multiplexes 32 bits down to 16 bits it can also be connected to the 386DX and 486 local bus. Nevertheless, the 542x chip can not be connected to the ISA bus and the VL bus at the same time. It makes no sense to implement mode switch logic that connectes the 542x chip to either the ISA or the VLB depending on which slot this card is inserted to, so I consider 542x VL cards running on 16 bit ISA a myth.

soviet conscript wrote on 2024-12-14, 02:02:

One advantage of this is many Cirrus Logic VLB cards support 2MB of RAM while ISA counterparts tend to top out at 1MB (if im remembering correctly). Not that 2MB on a video card makes much difference in DOS.

2MB on Cirrus cards only makes sense in certain special circumstances. There are already a lot of VOGONs thread educating about the uselessness of the 2MB upgrade on Cirrus 542x cards. Their main point is: As long as you don't use off-screen memory (for double-buffering, for containing sprites to be drawn, for caching fonts...), you don't need more memory than required for a single frame of video data. The memory bandwidth of the the CL-GD542x chip is so low that it can not display more than 1MB at any sensible refresh rate. Upgrading from 1MB to 2MB adds two modes. If I remember correctly, these are 1280x1024 256 colors @ 87Hz interlaced and 1024x768 65536 colors @ 87 Hz interlaced. Both of these modes provide sub-par quality on many CRTs and are incompatible with most LCDs.

As most consumers didn't have 2MB cards, there are very few if any VESA DOS games that use page flipping for double buffering if this would require more than 1MB of video RAM, even though the VESA BIOS Extensions did specify a way to access page flipping and hardware panning, if implemented on a card (most SVGA cards are capable of those features).

yep, you're correct. I jumped the gun with my response because a board me and a friend were testing recently. it's an Opti-495sx 386/486 board with a single VLB slot. Pretty much all sources report the VLB slot on this board is non-functional. My friend who was testing the board therefore was pretty confused when his Power! VLB card worked fine in it. after some thought though we did discover how the card has 2 separate chips and why it would function in the slot. We decided to test several other cards and the majority did indeed fail to POST but a handful of CL 542x cards did POST and seem to work to work which is why I came to my previous conclusions. yesterday we decided to test the board again and sure enough those same CL cards failed to work when placed in the board's 16-bit ISA slots. I'm assuming that even though the VLB slot on the board is technically none-functioning the CL cards don't use all of the VLB "functions" so as long as the card detects the extended VLB section is plugged in it will work?

soviet conscript wrote on 2025-02-13, 17:31:

yep, you're correct. I jumped the gun with my response because a board me and a friend were testing recently. it's an Opti-495sx 386/486 board with a single VLB slot. Pretty much all sources report the VLB slot on this board is non-functional. My friend who was testing the board therefore was pretty confused when his Power! VLB card worked fine in it. after some thought though we did discover how the card has 2 separate chips and why it would function in the slot. We decided to test several other cards and the majority did indeed fail to POST but a handful of CL 542x cards did POST and seem to work to work which is why I came to my previous conclusions. yesterday we decided to test the board again and sure enough those same CL cards failed to work when placed in the board's 16-bit ISA slots. I'm assuming that even though the VLB slot on the board is technically none-functioning the CL cards don't use all of the VLB "functions" so as long as the card detects the extended VLB section is plugged in it will work?

A Cirrus Logic chip connected to the VLB will only interface to the processor via the VLB. You can follow the traces on any CL-GD542x VLB card, and you won't find any address or data traces from the ISA bus to be connected to the Cirrus Logic chip. You might find the Reset and the IRQ2/9 pin connected, though, as well as power pins and the 14.318MHz oscillator. So if a Cirrus card POSTs in that board, it means the VL bus mostly works. The VL bus is not just used a s "token" to enable the chip to respond to ISA cycles. On the other hand, the CL cards are not very demanding on the VL bus, for example they typically run at 3 to 5 wait states. Maybe the board is unable to handle fast VL targets that try to perform zero-waitstate or one-waitstate cycles.

On the 386 and 486 local bus, the processor requests a bus cycle (by activating /ADS), and the addressed device has to actively signal when the cycle is done (by activating /RDY). There should be only one device that drives /RDY for every bus cycle. On boards without VL slots (and without a Weitek coprocessor or on-board graphics), the only device that drives /RDY is the chipset, after finishing a RAM transaction or after forwarding the cycle to the ISA bus. On VL boards, there is a signal on the VL slot that delegates the responsibility to gerate the /RDY signal from the chipset to the VL card. If only for a single cycle no device (neither the VL card, not the chipset) issues the /RDY response, the 486 locks up, waiting for that signal. So I suspect the problem with your board is a design issue in handling the cycle handover or forwarding the /RDY signal, which makes on very specific VL cards compatible with the board.

mkarcher wrote on 2024-12-14, 15:47:

soviet conscript wrote on 2024-12-14, 02:02:

In regards to VLB video cards working in ISA slots, some do. For instance the Power! Cards that have weitek chips also have a seperate VGA chip on the card. And only seem to use the VLB functionality if you load drivers or run Windows.

As these cards combine two separate graphics solutions (one is typically an OAK or a Weitek 5186 chip, the other one the Power 9000) onto one card, every application that just uses the VGA-compatible part which is a plain old ISA VGA will work without VLB interaction, unless the card initialization during POST requires interacting with the Power 9000 chip.

Since the Diamond Viper VLB also came as a Diamond Viper PCI with the same components, how would they have dealt with hooking up the Oak chip to PCI? Since it isn't as simple as having the ISA connector right there in that case.

jakethompson1 wrote on 2025-02-13, 22:41:

Since the Diamond Viper VLB also came as a Diamond Viper PCI with the same components, how would they have dealt with hooking up the Oak chip to PCI? Since it isn't as simple as having the ISA connector right there in that case.

Good question, but your premise is wrong. The Diamond Viper PCI does not have exactly the same components: It includes the Weitek P9001, which is not present on the Viper VLB. I strongly suspect the P9001 contains a kind of (possibly limited functionality) PCI-to-ISA bridge to connect the OAK VGA chip and the Booktree DAC to the PCI bus.