Re: 7854 RAM card upgrade only - any interest?

Cliff Carrie

The wiring diagram of the new Tek A28 board answers one mystery and raises another one. First, the vacant chip sites are for 2732 ROMs, not for added RAM.

With the other address map reserved areas you have identified and our lack of information about the firmware, I think this means we have no practical way to increase the RAM beyond the existing 8K words. Mystery solved, but no new goodies. We almost certainly do not need the vacant chip sites on our new card.

You mentioned that Tek somehow "sandwiched" the patch ROM content into the latest ROMs along with the existing coed. This is probably not quite true. The patch ROM and the FPLA chip act together to overlay bits of ROM code. On the new card, merging the patched code into the base ROMs probably requires no added space because the patches effectively replace bits of the earlier version code. The MPU gets either the original code or a replacement overlay depending on what the FPLA selects. The new ROMs roll the patches into the base code, eliminating the need for overlays.

Second, and a new mystery, the new Tek memory card has no connections for the Memory Backup / Self Test switch on the back panel of the scope. The switch may therefore be wired into some other card (MPU?). I will look into the old style MPU board tomorrow to see if the BAT line goes anywhere. It does go from the rear panel connector board to both the RAM and the MPU boards, but I don't see it in the MPU board diagram.


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