Certainly! The data sheets are different, but the parts are the same. The data sheet simply describes how the part was tested. With rare exceptions, the internal circuits are identical between HC and HCT logic. The only change is that HCT parts have a lower input switching threshold voltage. Do you have any references that show otherwise?PokeMon wrote:They are interchangeable from logic function but have not (definetely not !) internal design and not same data characteristic. Do you ever read datasheets?Lee Hart wrote: HC and HCT are essentially interchangeable. There is no internal difference...
I have done exactly that. I find that HC and HCT are interchangeable in any circuit where the input threshold voltage difference is not an issue. For example, I have been selling this little computer for several years http://www.sunrise-ev.com/MembershipCard.htm. I've mixed HC and HCT chips, from various vendors, and operated it on supply voltages from 3v to 5v. I have never had any issues in mixing the two families, as long as there are no bipolar TTL parts to produce weak high logic levels.PokeMon wrote:...the HCT series are made for 5V operation voltage only as the HC series allows a wide range of operation from 2.0 Volts to 6.0 Volts. Try to compare HC and HCT at a different supply voltage and you will be surprised about their behaviour.
PokeMon wrote:this could be solved and easily managed with a custom program in FAST mode and a special written keyboard input routine.Lee Hart wrote:The root cause is that Sinclair's cheap design does not meet TTL logic level specs at the inputs of U10... There is a lot of noise on the address bus...
That is a good approach, and I tried it. The problem is that the keyboard reads correctly most of the time. I have a good scope, but it is not a storage scope. I have no way to trigger on a bad read, or capture what happened during it. Even though a 10:1 scope probe has low loading, it still affects operation. Take a look at the ZX80 data and address buses. They are amazingly noisy!
I am sure someone with a logic analyzer could find this problem quickly. But I do not have access to one, and have to rely on simpler methods.