Mixing 74 LS/HCT with diode logic

ericgibbs

Joined Jan 29, 2010
8,733
hi John,
Welcome to AAC.
RDL logic was very popular in the early days of semiconductors, what sort of speed did you have in mind and how wide will the OR gate be.?
E
 

Thread Starter

John Bradley

Joined Sep 14, 2019
18
Either 6 or 8 input at the moment. It only going into a Z80 based circuit at the moment but may have to go to 50Mhz in the end, if I decided to do an eZ80 version. The 1N4148 seem to have a switch time of 3ns which is far faster than the 74HCT/HC I will be using https://github.com/flypie/Ace-2019
 

Thread Starter

John Bradley

Joined Sep 14, 2019
18
It would be but for the fact that eveyonehas the marked down as obsolete except for the hcc4078B, which at nearly £5 a go seem a little expensive.
 

Thread Starter

John Bradley

Joined Sep 14, 2019
18
hi,
Found this on the web, it maybe a quantity price.???

https://www.technobotsonline.com/74hc4078-8-input-or-nor-gate.html
Problem is it is HC what I really need is HCT at the moment. The final version I'll be able to drop to 3.3 but these risk reduction versions have to work with Z80s which are 5v. Also, they seem to be marked as obsolete on Mouser etc. It would be a shame to redesign the board and have the chips become unavailable. https://www.mouser.co.uk/Search/Refine?Keyword=74HC4078
 

nsaspook

Joined Aug 27, 2009
6,278

ericgibbs

Joined Jan 29, 2010
8,733
hi,
I have still got 3 Sharp MZ80K's in the garage, gathering dust.
They have been up graded in a number of ways.
Most of my products were Z80A based, used assembler coding.

E
 

nsaspook

Joined Aug 27, 2009
6,278
Building z80 class machines seem to be popular pass time.
It's like rebuilding old cars. Do we use modern internal chassis parts to make it better or keep it all original. There's a lot to be said for both approaches if it's for our own enjoyment.
 

Thread Starter

John Bradley

Joined Sep 14, 2019
18
Sweet. Good luck with your project, looks like fun. I have a few old Z80 machines I designed a long time ago that have been integrated with a modern controller for memory and I/O.
https://forum.allaboutcircuits.com/threads/memio-emulator-for-z80.117003/
These people have 291 of the HCTs in stock but you have to request a quote to get a price... https://www.realcomponents.com/results.html?part=74HCT4078&rcllc=Bing
Thanks I'll look into it.
These people have 291 of the HCTs in stock but you have to request a quote to get a price... https://www.realcomponents.com/results.html?part=74HCT4078&rcllc=Bing
Thanks I will take a look.
 

nsaspook

Joined Aug 27, 2009
6,278
I think some take it a little far though
This 6502 Made From 74-Series Logic Can Run At 20 MHz

. https://hackaday.com/2018/12/15/this-6502-made-from-74-series-logic-can-run-at-20-mhz/

8080 video processor with lots of TTL glue, 8080 cpu and ram/rom memory from a 1979 video game (Mastermind) system I designed. The Z80 board replaced the 8080 later.
The computer handled the duties of the Codemaker for a single player game-play.
https://arxiv.org/pdf/1207.1315.pdf

There is no such thing as a little far. :D
 
Last edited:

Thread Starter

John Bradley

Joined Sep 14, 2019
18
I've just done a test with a 74LlS02 on a breadboard. The output from Gate A was fed into one of the diode gate inputs, the output from the diode gate was being fed into one of the C gate pins with the output driving an LED and it worked as expected. Not sure if this proves anything. Intially I had the LS02 driving the diodes and straight to an LED, the LED was a lot dimmer when the input to the gate wa from the LS02 then when driven from the power rail, when driven by the LS02 in the final configuration it returned to full brightness.

 
Top