UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Slothie · 20th Dec 2018, 1:57 am

While the 2114 is almost pin compatible with the 2111. the ground and write enable pins have been swapped and the 2 extra chip enables have been lost, so I'd have to add in some extra gates and it would be hard to add jumpers to cater for it due to the ground pin moving, so its one or the other rather than an option.

As for fully mapping the extra memory, it's a big change but I get your point! It means ripping out all the address decode logic and replacing it, I've worked out whats required with my logic simulator but it'll need reworking to simplify and use 74 gates you can actually get (I'm thinking a 74ls138 and some AND gates), but you end up with 1.5k RAM with "holes" in for the display and ram/io at $D00-$DFF and $800-$8FF respectively. I think I would do this as a "Rev 3" board a little later, since I do have 3 sets of 4 2111 compatible chips at the moment.

If I'm putting the address and data on the edge connector of course you could just leave out the 2111's and put in memory of your choice with logic that maps to the right places on an external card!

Anyway I'm not fully decided yet, I think I shall think about it over Christmas!

20th Dec 2018, 1:57 am	#138
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: MK14 schematic revisions While the 2114 is almost pin compatible with the 2111. the ground and write enable pins have been swapped and the 2 extra chip enables have been lost, so I'd have to add in some extra gates and it would be hard to add jumpers to cater for it due to the ground pin moving, so its one or the other rather than an option. As for fully mapping the extra memory, it's a big change but I get your point! It means ripping out all the address decode logic and replacing it, I've worked out whats required with my logic simulator but it'll need reworking to simplify and use 74 gates you can actually get (I'm thinking a 74ls138 and some AND gates), but you end up with 1.5k RAM with "holes" in for the display and ram/io at $D00-$DFF and $800-$8FF respectively. I think I would do this as a "Rev 3" board a little later, since I do have 3 sets of 4 2111 compatible chips at the moment. If I'm putting the address and data on the edge connector of course you could just leave out the 2111's and put in memory of your choice with logic that maps to the right places on an external card! Anyway I'm not fully decided yet, I think I shall think about it over Christmas!