First post, by carlostex
- Rank
- l33t
On my Socket 7 builds i rather prefer ATX boards, and i became fond of motherboards with 4 ISA slots. Reason is that i like having lots of sound standards to enjoy, playing the same games with different sounding music leads to a different experience.
I've been craving to get this Industrial DFI board, the ITOX 586, with 6 ISA and 2 PCI slots and even integrated S3 Trio graphics. Finding these boards is quite difficult, so i've been settling on my ASUS TX-97XE.
One of the things i find interesting is undocumented FSB settings. I've been impressed how i could make my 286 to behave close to a 4.77MHz XT class machine. Using an 8MHz clock oscillator, i found myself playing games like Digger or Moon Patrol very close to what a real XT would feel. In fact, Digger felt really nice at its speed was pretty much around the sweet spot.
Some motherboards, have frequency generators with undocumented settings that allow you to divide the reference clock (coming from a 14.318MHz osci) by 2 effectively giving an FSB of 7.159 MHz. This became a very standard ISA bus speed for 486 motherboards at least.
On my case i'm wondering how easy would be to replace a ICS9169CJ-272 (which comes with my TX-97XE) and replace it with a ICS9169CJ-27 which differes from the former to allow exactly that Reference clock divided by 2. Using my K6+ CPU, i could clock it at around 15MHz with a 2x multiplier setting.
At 15MHz it's difficult to say how fast the system with be, but i believe around a 386DX. The K6 is much faster than a 386 but it is hampered by running only at 15MHz and a 7Mhz bus. I would say maybe around a 386DX 33 or touching a 40MHz.
Reaching 386 speeds is nothing remarkable that can be done by turning off caches, but turning internal cache off could potentially make the system as slow as a early 286 and all caches off could even turn the system into a XT class machine. This could result in the most versatile DOS machine ever!!
Now this would require some hardware modding, i checked datasheets and both frequency generators are pin compatible. Soetimes you find boards with one or the other but unfortunately ASUS boards (both the TX-97XE or the TXP4-X) are mostly found with the ICS9169CJ-272, which doesn't allow to select REFERENCE/2.
If i ever get a spare board and if i can source ICS9169CJ-27 frequency generators i'll be definitely be trying this. I think the biggest challence is to desolder the old chip first. I was very encouraged to try SMT soldering when i saw how easy high quality EDSYN solder flux makes it to solder SMT components.
