Super Kickstart

[mechy]

The other ROM positions (U182, U183) are for ICs that have a different pinout such as the 27C220 and 27C2048.

The standard positions U180, U181 are for pinouts to suit 27C100, 27C200, etc.

You can't have two types of ROMs fitted at once, although if you were to disconnect _ROMEN to each ROM pair and fit a toggle switch so that only one pair can be active at once, then it would be possible to switch between the two.  You'd need to add pullup resistors on the ROM _OE lines for when nothing is connected.

But it's a lot nicer use to use a ROM switcher module or BlizKick instead of chopping the hardware around.

Are you sure about the type of roms the 2 sockets can use? I know the 27c220,2048 etc can replace the rom tower(which used 27c200,400 etc) on the rev 7 boards direct(u180,181) eliminating it ,but i seem to recall i tried the 27c220/2048 etc in the u182,u183 positions and it did not work. My memory may be failing me but those sockets don't seem to work for any rom/eprom pinouts i found.

Have you actually used those sockets?

Mech

[mechy]

All of my hardware development work was based on the U180, U181 positions so I've not personally used the U182, U183 positions.

I've seen various examples of A3000s with 27C220 ROMs in U182, U183 so I would assume they work on at least some PCB revisions.

If you're having issues, then compare the pin detail from the EPROM datasheet to what's presented on the A3000 hardware.

A potential trap for hardware newbies is that the high order address line(s) such as A17 (pin 1) is floating on certain revisions of the A3000D main board, including rev 8.9 and possibly earlier ones.  Was fixed (tied to ground) in rev 9/03.

The result is that if you're using EPROMs larger than 256kB x 16 (4Mbit) then the high order address line floats and may cause unpredictable results.  I know some memory devices refuse to work correctly at all if any of the address lines are floating, even if the data image is mirrored to both halves of the address range.

Good info there, it may of been a case of bigger eproms and the floating aqddress line.I was testing on a old rev7 at the time i believe. i had sworn it worked but originally i may of tested on a 9/02.

thanks for the info.

mech