TI-99 4a memory question - 64k possible by 2x32k cards?

[Space Centurion]

Hi all, just wondering if it is possible to get 64k on the 4a by simply adding a second 32k card in the PEB. I've read that the 4a can address 64k of ram, but I'm too afraid to try it on my own and blow something up if it does not work. So, just wondering if any one has any experience with this. Thanks.

[am1933]

As far as I am aware the you can install as many memory cards as you want-unfortunately the TI will only recognise one of them.

[Space Centurion]

Yeah, that doesn't surprise me. With all that room in the PEB, you figure that one could just add additional memory (to a point). All well.......I might get brave and try it......

[Space Centurion]

Well...turns out Moonsweeper was right. You can add as much RAM to the PEB as you want, but it will only recognize one of them. Or possibly all of them, just accessing them all at the same time in parallel. In any event, nothing blew up, no smoke was released from the ICs, and the TI is still 32k. Ok, 48k total!

[+Ksarul]

The only way to have a memory card in the PEB that actually provides more than 32K is to have a card designed to work using more space installed. The most common of those cards would be the Super AMS board, which gives up to 1024K--and which is bank switched. There are a few programs and utilities that make use of this feature out there--and new things for it are still being developed, although at a slow pace. The RAMBO modification for the Horizon RAMDisk provided a similar bank switched user space. The only other option I know of was the prototype 128K card produced by TI. It actually gave you 48K all the time by working as a 32K card which put some additional RAM in the DSR space at >4000 and in the cartridge space at >6000. The rest was bank switched at need by user programs designed to use it.

 

Multiple 32K cards in the PEB give no advantage whatsoever, as the TI OS expects the memory card to fit into a specific, 32K portion of the memory map, and all memory cards automatically fall into that same space unless they were designed to do something differently, as identified for the three examples above.

[hhos]

.....Ten years later.... I don't know that it will matter to anyone now, or even at any time for that matter, but if the info from the "Hardware Manual for the Texas Instruments 99/4A Home Computer", page 8-4(81), is reliable, it is possible to have more than one 32K board in the PEB.  Pen 14 of the PAL on the memory board is described with the following boolean expression:

 

   PCBEN*MEMEN*AMC*AMB*AMA*/A1*A2 + PCBEN*MEMEN*AMC*AMB*AMA*A0*A1

 

So if you had a way to alter to the signals on the AMC-AMB-AMA bus(CBA-bus), you could switch between the boards.  It's not a particularly elegant system, but TI put these in there.  You could have up to seven boards this way, using every slot in the PEB,  No disk drives, no RS232s, etc.  The memory board is the only hardware that I've run across that uses these lines, and only for CBA-bus=111.  It's not very useful, but I have to wonder, what did they have in mind for these lines when they included them in the PEB bus design?  I can't help but try to include them anytime I consider designing new hardware for this platform. 😄  For instance, is it possible to stack PEBs?  Pure insanity!!😆

 

HH