On 03/09/2015 09:05, simon wrote: Ow. I don't have a list, but I do have a copy of the 1976 Signetics ICs databook, which lists a lot of 82xx logic. I've not checked one of my M8330 boards but I guess that's what you need. 8235 is a quad (4-bit) 2-input multiplexer - with a twist. It has open collector outputs and two control inputs. The twist is that one of each pair of inputs is non-inverting, the other is inverting, and the idea is that by tying the two inputs together you can use the control inputs to make the outputs the TRUE or COMPLEMENT of the input data, eg to feed to an adder. The data sheet is two pages, which I can scan if you want. The An and Bn data inputs are pins 1 and 2, 6 and 5, 10 and 11, 15 and 14; corresponding f0 to f3 outputs are pins 3, 4, 12 and 13. S0 and S1 are pins 9 and 7. Vcc is pin 16, GND is 8. Truth table: S0 S1 fn ---- ---- ---- 0 0 /An.Bn 0 1 Bn 1 0 /An 1 1 1 I like the last paragraph of the description. "The 8234 and 8235 designs have open collector outputs which permit direct wiring to other open collector outputs (collector logic) to yield 'free' four-bit words. As any as one hundred four bit words can be multiplexed by using up to fifty 8234/8235 in WIRED-AND mode." Good thing DEC didn't go quite that far. -- Pete Pete Turnbull

On 03/09/2015 14:52, Kyle Owen wrote: Impressive! -- Pete Pete Turnbull

On 09/03/2015 08:49 PM, dwight wrote: A GAL should also be useful--and maybe a bit more flexible. To emulate the OC outputs, one can simply manipulate the output enable so that a '1' output is High-Z and '0' is, well, '0'. I believe individual oput tristate control is allowed in non-registered mode for GALs. A PALCE should also work. A 20 pin PLCC should fit on a DIP-sized PCB. --Chuck

Yup. I have done the same kind of thing with GALs (which offer the convenience of re-programming, though not the longevity of a PAL.) Did this as a backup for the Signetics chips on a Mark 8. You can see them in this Flickr stream - I had both "normal" and open collector variants, and designed both chip-specific and generic boards for chip replacement (I expect to run into the issue with DTL as well). https://www.flickr.com/photos/100660569 at N02/albums/72157635953237715 BTW, I sent my PCBs out to Gold Phoenix PCB - http://www.goldphoenixpcb.com/ JRJ On 9/3/2015 10:49 PM, dwight wrote:

The idea for using the tristate control for an OC output has been used many times before. An example is on the SwyftCard for the Apple 2e. It needed a OC for the reset as I recall and the PAL used that trick. The only possible issue is the limited current drive for older DTL circuits. Dwight