On Fri, 20 Oct 2023 07:50:14 -0700 (PDT), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Friday, October 20, 2023 at 10:42:42?AM UTC-4, Glen Walpert wrote: >> On Thu, 19 Oct 2023 20:01:07 -0400, Joe Gwinn wrote: >> >> > On Thu, 19 Oct 2023 16:37:39 -0700, john larkin <j...@650pot.com> wrote: >> > >> >>On Thu, 19 Oct 2023 13:49:12 -0700, John Robertson <j...@flippers.com> >> >>wrote: >> >> >> >>>I'd like to verify that 74F##(#) family can replace the 74##(#) chips >> >>>which are getting rather expensive or of unknown (?) quality if one is >> >>>second sourcing them from folks like Unicorn, or eBay (shudder). >> >>> >> >>>I am well aware the 74LS has may replacements including the 74ALS, >> >>>74HCT, and others, but they only fan-out to 10 LS gates or 1 original >> >>>gates. >> >> >> >>74HC or 74HCT should drive many old 74xx parts. >> >> >> >>7400s only sourced about 1 mA at their inputs, and LS was 0.4 mA max. >> >>A 74HC or HCT should easily drive five 74xx and scores of 74LS gates. >> >> >> >>The hc/hct parts will be faster than the old TTLs, which could be a >> >>problem with old hairball logic. >> > >> > Yes. I've had to interface new kit to very old kit. The answer was >> > Schmitt trigger for signals coming into new, and RC filters going into >> > old. >> > >> > >> > Joe Gwinn >> > >> I recall some instances of people switching existing TTL designs to HC, >> and discovering that termination or better termination was required on >> clock and data lines. The RC filter should prevent that problem. > >That was the 3x faster output rise/fall time doing that. > >> >> I have a box of old IC's containing a bunch of 74xx parts in original Jim- >> Pak or Active Electronics packaging, mostly unopened, I could send the >> 74xx parts or the entire box for you to sort including various counters, >> shift registers, PLL's, more LS than plain TTL but contents largely >> unremembered, possibly old memory. The empty space is now more valuable >> than the parts to me, and I would rather pay postage to someone who can >> use them than throw them out. >> >> Glen >> >>>I have older games that need reliable 74## and won't work reliably with >> >>>the lower fan-out stuff. >> >>> >> >>>I have a Fairchild FAST DATA BOOK, but it doesn't actually say anywhere >> >>>I've read so far about how compatible it is with the original TTL >> >>>fan-outs. They do say that the F family are more susceptible to static >> >>>than 74S or 74LS so perhaps I will look at 74S in place of the >> >>>originals if they have a similar fan-out. >> >>> >> >>>Suggestions welcome! >> >>> >> >>>John :-#)#In the early days of AC logic, I was amazed to see well sub-nS edges from cheap parts. Some of the Tiny cmos parts are crazy fast. https://www.dropbox.com/scl/fi/iugv8wzmh3ie9zzmv8vpi/NC7SV74_2.JPG?rlkey=tkdj4ire4e92wixk57omm8k2o&dl=0
Substitutes for the 7400 family....
Started by ●October 19, 2023
Reply by ●October 21, 20232023-10-21
Reply by ●October 21, 20232023-10-21
On Sunday, October 22, 2023 at 12:54:17 AM UTC+11, John Larkin wrote:> On Fri, 20 Oct 2023 07:50:14 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Friday, October 20, 2023 at 10:42:42?AM UTC-4, Glen Walpert wrote: > >> On Thu, 19 Oct 2023 20:01:07 -0400, Joe Gwinn wrote: > >> > >> > On Thu, 19 Oct 2023 16:37:39 -0700, john larkin <j...@650pot.com> wrote: > >> > > >> >>On Thu, 19 Oct 2023 13:49:12 -0700, John Robertson <j...@flippers.com> > >> >>wrote: > >> >> > >> >>>I'd like to verify that 74F##(#) family can replace the 74##(#) chips > >> >>>which are getting rather expensive or of unknown (?) quality if one is > >> >>>second sourcing them from folks like Unicorn, or eBay (shudder). > >> >>> > >> >>>I am well aware the 74LS has may replacements including the 74ALS, > >> >>>74HCT, and others, but they only fan-out to 10 LS gates or 1 original > >> >>>gates. > >> >> > >> >>74HC or 74HCT should drive many old 74xx parts. > >> >> > >> >>7400s only sourced about 1 mA at their inputs, and LS was 0.4 mA max. > >> >>A 74HC or HCT should easily drive five 74xx and scores of 74LS gates. > >> >> > >> >>The hc/hct parts will be faster than the old TTLs, which could be a > >> >>problem with old hairball logic. > >> > > >> > Yes. I've had to interface new kit to very old kit. The answer was > >> > Schmitt trigger for signals coming into new, and RC filters going into > >> > old. > >> > > >> > > >> > Joe Gwinn > >> > > >> I recall some instances of people switching existing TTL designs to HC, > >> and discovering that termination or better termination was required on > >> clock and data lines. The RC filter should prevent that problem. > > > >That was the 3x faster output rise/fall time doing that. > > > >> > >> I have a box of old IC's containing a bunch of 74xx parts in original Jim- > >> Pak or Active Electronics packaging, mostly unopened, I could send the > >> 74xx parts or the entire box for you to sort including various counters, > >> shift registers, PLL's, more LS than plain TTL but contents largely > >> unremembered, possibly old memory. The empty space is now more valuable > >> than the parts to me, and I would rather pay postage to someone who can > >> use them than throw them out. > >> > >> Glen > >> >>>I have older games that need reliable 74## and won't work reliably with > >> >>>the lower fan-out stuff. > >> >>> > >> >>>I have a Fairchild FAST DATA BOOK, but it doesn't actually say anywhere > >> >>>I've read so far about how compatible it is with the original TTL > >> >>>fan-outs. They do say that the F family are more susceptible to static > >> >>>than 74S or 74LS so perhaps I will look at 74S in place of the > >> >>>originals if they have a similar fan-out. > >> >>> > >> >>>Suggestions welcome! > >> >>> > >> >>>John :-#)# > In the early days of AC logic, I was amazed to see well sub-nS edges > from cheap parts. > > Some of the Tiny cmos parts are crazy fast. > > https://www.dropbox.com/scl/fi/iugv8wzmh3ie9zzmv8vpi/NC7SV74_2.JPG?rlkey=tkdj4ire4e92wixk57omm8k2o&dl=0But they don't drive transmission lines well. The charm of ECL and ECLinPs and LVDS is that it does. If you can confine your logic inside a single big fast programmable logic device, this doesn't matter so much, but fast edges don't stay fast for long if you stick them into unterminated transmission lines, and reflected fast edges can play havoc. -- Bill Sloman, Sydney
Reply by ●October 21, 20232023-10-21
lørdag den 21. oktober 2023 kl. 15.54.17 UTC+2 skrev John Larkin:> On Fri, 20 Oct 2023 07:50:14 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Friday, October 20, 2023 at 10:42:42?AM UTC-4, Glen Walpert wrote: > >> On Thu, 19 Oct 2023 20:01:07 -0400, Joe Gwinn wrote: > >> > >> > On Thu, 19 Oct 2023 16:37:39 -0700, john larkin <j...@650pot.com> wrote: > >> > > >> >>On Thu, 19 Oct 2023 13:49:12 -0700, John Robertson <j...@flippers.com> > >> >>wrote: > >> >> > >> >>>I'd like to verify that 74F##(#) family can replace the 74##(#) chips > >> >>>which are getting rather expensive or of unknown (?) quality if one is > >> >>>second sourcing them from folks like Unicorn, or eBay (shudder). > >> >>> > >> >>>I am well aware the 74LS has may replacements including the 74ALS, > >> >>>74HCT, and others, but they only fan-out to 10 LS gates or 1 original > >> >>>gates. > >> >> > >> >>74HC or 74HCT should drive many old 74xx parts. > >> >> > >> >>7400s only sourced about 1 mA at their inputs, and LS was 0.4 mA max. > >> >>A 74HC or HCT should easily drive five 74xx and scores of 74LS gates. > >> >> > >> >>The hc/hct parts will be faster than the old TTLs, which could be a > >> >>problem with old hairball logic. > >> > > >> > Yes. I've had to interface new kit to very old kit. The answer was > >> > Schmitt trigger for signals coming into new, and RC filters going into > >> > old. > >> > > >> > > >> > Joe Gwinn > >> > > >> I recall some instances of people switching existing TTL designs to HC, > >> and discovering that termination or better termination was required on > >> clock and data lines. The RC filter should prevent that problem. > > > >That was the 3x faster output rise/fall time doing that. > > > >> > >> I have a box of old IC's containing a bunch of 74xx parts in original Jim- > >> Pak or Active Electronics packaging, mostly unopened, I could send the > >> 74xx parts or the entire box for you to sort including various counters, > >> shift registers, PLL's, more LS than plain TTL but contents largely > >> unremembered, possibly old memory. The empty space is now more valuable > >> than the parts to me, and I would rather pay postage to someone who can > >> use them than throw them out. > >> > >> Glen > >> >>>I have older games that need reliable 74## and won't work reliably with > >> >>>the lower fan-out stuff. > >> >>> > >> >>>I have a Fairchild FAST DATA BOOK, but it doesn't actually say anywhere > >> >>>I've read so far about how compatible it is with the original TTL > >> >>>fan-outs. They do say that the F family are more susceptible to static > >> >>>than 74S or 74LS so perhaps I will look at 74S in place of the > >> >>>originals if they have a similar fan-out. > >> >>> > >> >>>Suggestions welcome! > >> >>> > >> >>>John :-#)# > In the early days of AC logic, I was amazed to see well sub-nS edges > from cheap parts. > > Some of the Tiny cmos parts are crazy fast. > > https://www.dropbox.com/scl/fi/iugv8wzmh3ie9zzmv8vpi/NC7SV74_2.JPG?rlkey=tkdj4ire4e92wixk57omm8k2o&dl=0and if you stick that in a 40 year old hairball, it'll get "interesting"
