the /AS is the address strobe, yes...
Starting with the Backlit portable, they removed the /AS in the RAM connector and replaced it with a signal, known as /RAM.CS
This signal is controlled by an external address decoder network, which actually sits between the ROM socket, and the RAM itself. a series of 74 series gates. but I digress...
This /RAM.CS will only assert within the first 5MB of address space. After that, the signal no longer gets asserted. Therefore, on the M5126, you have a RAM ceiling of 5MB in the RAM slot. PDS is an exception though because you have access to the entire bus so these limitations dont exist.
but since I didnt feel like dealing with the Eurocard connectors, or the PDS, I designed the card to fit in the existing RAM slot.
So.... In order to gain full addressing on the backlit portable via the RAM slot, you have to pick off the /AS address strobe signal either from the PDS, or from the ROM slot. Since ROM is still attached directly to the bus, and not isolated through an external decoder.
The catch is, after 5+MB the RAM decoder network no longer generates a /DTACK signal to tell the processor that the data transfer was successful.
So, I am thinking that since I didnt hook the DTACK line up, it was causing a ton of bus errors even though the system information was showing the full 8MB of RAM.
If I use the /RAM.CS signal instead of /AS, everything works great. But only sees 5MB as expected. If I remove the jumper that connects to /RAM.CS and replace it with a wire that goes to /AS instead, It shows the full 8MB of RAM. But every time an application launches and uses the extended RAM (RAM past 1MB), the backlight flickers on and off extremely rapidly, at the same pace as the RAM accessing occurs.
so i think the DTACK connection not being made is an issue, OR, since my /AS wire clip lead was so long and coiled, it was distorting the signal to the RAM card causing issues with data transfers in and out of RAM.
Funny thing though... no bombs, or system errors/sad macs. Just kept right on chugging with backlight flickering. Soon as I exited microsoft word 5.1, it quit. backlight stayed on.