Re: Apple IIe Tech Note #5 /INH Line

[aiiadict@gmail.com]

On Thursday, September 20, 2012 10:47:46 AM UTC-7, a2retro wrote:
> the link is http://www.1000bit.it/support/manuali/apple/technotes/aiie/tn.aiie.05.html 
> Interesting on page 5-59 of that book is a 1K Auxiliary RAM card that 
> uses a 2159B-2 (2158B-2) RAM chip and that chip has a single R/W/
> line.
> 

Thanks for the link.  I thought this part was interesting because I've wondered if you could do this before: (co-processor to other card communication without using the main RAM or CPU)

Another Feature

For those of you who love to muck around in the guts of the Apple IIe, one more feature has been added to the /INH function. The /INH line will also override DMA accesses to memory on the motherboard. This override means that if a peripheral card uses DMA to read or write to memory, another peripheral card could pull the /INH line and process the DMA access. An example of this would be a co-processor card using the memory on a RAM card in another slot. Rather than have the co-processor write to the memory on the motherboard then have the 6502 write to the RAM card, the co-processor can write to an address that the RAM card recognizes. The RAM card could then pull the /INH line and it would be free to read or write the data bus. This technique could also be used by a co-processor to write directly to a printer card in another slot.