Ttl 7400 Series

There has been a resurgence in retro technologies in recent years, such as projects built using 7400 series TTL. Such projects are often computers or calculators etc.

Why I hate 7400 series TTL

I always explain that I loathe 7400 series TTL and have finally decided to explain my reasons, so you be the judge ?

In the early 1970’s I assembled a new project, a 7400 series TTL ‘roll form controller’. This innovative machine used a rotary encoder (made of reed relays and magnets, but that’s another story) which measured the length of steel sheet that was shaped by the roll form machine steel rollers into various profiles such as roofing iron or beams used in building construction.

In the late 1970’s I was building digital industrial alarm systems every day, they were 19” racks full of 7400 series TTL cards which latched alarms into ‘annunciatior panels’. The panels went into large industrial plant ‘control rooms’ which looked like scifi films, i.e. large boards consisting of square switches with lights inside them. The button itself was engraved with the name of the alarm, i.e. “motor-1”

Hundreds, perhaps thousands of these buttons would be in the plant control rooms, all wired to the TTL racks, which were in turn wired to switches in the plant. Each alarm board ‘alarm’ had a choice of a NO or NC switch input, all TTL inputs used 220 ohm resistors for pull up or down etc.

When a alarm was activated, the light in the switch would flash, and pressing the switch would reset the flip flop that had latched the alarm. The control room operatorse spent their days pressing those switches because of the huge number of false alarms that always plagued those systems.

The standard proceedure was ‘if a alarm is flashing, press the button to see if it’s a real alarm’

plus a engineer who was a really nice guy doing his first project after graduating as a EE from university worked at the same firm, we had about 10 such engineers. He developed what he called the ‘CACC’ it was a a ‘calculator assisted coordinate controller’ and the idea was the calculator like control pad hung from a massive overhead interior crane and one entered the coords to automatically send the crane to any location in a large factory

the PCB he made was about a foot square and full of 7400 series TTL as thats all we had then, apart from a National PACE 16 bit cpu development system, but that was in use and anyway would have been too expensive for the CACC project the CACC all worked nicely, but had one fatal flaw, intermittently it would forget the coordinate! the engineer put this down to the TTL being reset by a super fast ‘runt’ pulse, probably caused by electrical mains spikes caused by the hundreds of welders and motors in the huge factory we had a small R&D dept in he couldnt see the pulse, he spent months trying to find it and work around it but it persisted in those days a foot square PCB was a big deal, especially one jammed with 7400 chips, so he didnt design another in the end the poor guy was sacked for the failure of his project what a blow to a really friendly and smart EE on his first project, I really felt sorry for him those are the main reasons that I loathed 7400 series TTL in the 1970’s I cant really think of better reasons to loathe any technology than unreliability that you cant fix because you cant diagnose it then 4000 series CMOS logic came out and all those issues Ive described above just stopped instantly everyone was pulling 7400 series and replacing them with 4000 series, and all the bughy projects were now working 100% reliably the 4000 series were running from 12v and had a huge noise margin, and I rekon you could hear the mas MrMobius, in thise days I was building digital industrial alarm systems every day, they were 19” racks full of TTL cards which latched alarms into ‘annunciatior panels’ the panels went into large industrial plant ‘control rooms’ which looked like scifi films, ie large boards consisting of square switches with lights inside them. The button itself was engraved with the name of the alarm, i.e. “motor-1” and hundreds, perhaps thousands of these buttons would be in the plant control rooms, all wired to the TTL racks, which were in turn wired to switches in the plant each alarm board ‘alarm’ had a choice of a NO or NC switch input all TTL imputs used 220 ohm resistors for pull up or down etc when a alarm was activated, the light in the switch would flash, and pressing the switch would reset the flip flop that had ltched the alarm the control room people spent their days pressing those switches because of the huge number of false alarms that always plagued those systems so the standard proceedure was ‘if a alarm is flashing, press the button to see if it’s a real alarm’ this was the same curse that plagued the roll form guilotine batch controllers plus a engineer who was a really nice guy doing his first project after graduating as a EE from university worked at the same firm, we had about 10 such engineers. He developed what he called the ‘CACC’ it was a a ‘calculator assisted coordinate controller’ and the idea was the calculator like control pad hung from a massive overhead interior crane and one entered the coords to automatically send the crane to any location in a large factory the PCB he made was about a foot square and full of 7400 series TTL as thats all we had then, apart f MrMobius, in thise days I was building digital industrial alarm systems every day, they were 19” racks full of TTL cards which latched alarms into ‘annunciatior panels’ the panels went into large industrial plant ‘control rooms’ which looked like scifi films, ie large boards consisting of square switches with lights inside them. The button itself was engraved with the name of the alarm, i.e. “motor-1” and hundreds, perhaps thousands of these buttons would be in the plant control rooms, all wired to the TTL racks, which were in turn wired to switches in the plant each alarm board ‘alarm’ had a choice of a NO or NC switch input all TTL imputs used 220 ohm resistors for pull up or down etc when a alarm was activated, the light in the switch would flash, and pressing the switch would reset the flip flop that had ltched the alarm the control room people spent their days pressing those switches because of the huge number of false alarms that always plagued those systems so the standard proceedure was ‘if a alarm is flashing, press the button to see if it’s a real alarm’ this was the same curse that plagued the roll form guilotine batch controllers plus a engineer who was a really nice guy doing his first project after graduating as a EE from university worked at the same firm, we had about 10 such engineers. He developed what he called the ‘CACC’ it was a a ‘calculator assisted coordinate controller’ and the idea was the calculator like control pad hung from a massive overhead interior crane and one entered the coords to automatically send the crane to any location in a large factory the PCB he made was about a foot square and full of 7400 series TTL as thats all we had then, apart from a National PACE 16 bit cpu development system, but that was in use and anyway would have been too expensive for the CACC project the CACC all worked nicely, but had one fatal flaw, intermittently it would forget the coordinate! the engineer put this down to the TTL being reset by a super fast ‘runt’ pulse, probably caused by electrical mains spikes caused by the hundreds of welders and motors in the huge factory we had a small R&D dept in he couldnt see the pulse, he spent months trying to find it and work around it but it persisted in those days a foot square PCB was a big deal, especially one jammed with 7400 chips, so he didnt design another in the end the poor guy was sacked for the failure of his project what a blow to a really friendly and smart EE on his first project, I really felt sorry for him those are the main reasons that I loathed 7400 series TTL in the 1970’s I cant really think of better reasons to loathe any technology than unreliability that you cant fix because you cant diagnose it then 4000 series CMOS logic came out and all those issues Ive described above just stopped instantly everyone was pulling 7400 series and replacing them with 4000 series, and all the bughy projects were now working 100% reliably the 4000 series were running from 12v and had a huge noise margin, and I rekon you could hear the massive sighs of relief from EE’s worldwide who’s jobs had just been saved in the nick of time but it was too late for lots of EE’s like ‘Ray X’ who had lost their first jobs because of 7400 seried TTL by comparison the National PACE job https://patents.google.com/patent/US4205230 worked flawlessly, a CMOS 16 bit cpu, some small number of TTL such as quad tristate latches etc but mainly the CPU, PROM, ram and analog parts life was hard in those days, the brilliant EE who designed that project was also sacked when he wouldnt release the project for billing as it ‘wasnt quite finished’ … after he was sacked, I lost interest in that company and resigned, too many brilliant EE’s I liked had been sacked as a mere assembly technician I was immune from being sacked unless I really made some stupid screwuprom a National PACE 16 bit cpu development system, but that was in use and anyway would have been too expensive for the CACC project the CACC all worked nicely, but had one fatal flaw, intermittently it would forget the coordinate! the engineer put this down to the TTL being reset by a super fast ‘runt’ pulse, probably caused by electrical mains spikes caused by the hundreds of welders and motors in the huge factory we had a small R&D dept in he couldnt see the pulse, he spent months trying to find it and work around it but it persisted in those days a foot square PCB was a big deal, especially one jammed with 7400 chips, so he didnt design another in the end the poor guy was sacked for the failure of his project what a blow to a really friendly and smart EE on his first project, I really felt sorry for him those are the main reasons that I loathed 7400 series TTL in the 1970’s I cant really think of better reasons to loathe any technology than unreliability that you cant fix because you cant diagnose it then 4000 series CMOS logic came out and all those issues Ive described above just stopped instantly everyone was pulling 7400 series and replacing them with 4000 series, and all the bughy projects were now working 100% reliably the 4000 series were running from 12v and had a huge noise margin, and I rekon you could hear the massive sighs of relief from EE’s worldwide who’s jobs had just been saved in the nick of time but it was too late for lots of EE’s like ‘Ray X’ who had lost their first jobs because of 7400 seried TTL by comparison the National PACE job https://patents.google.com/patent/US4205230 worked flawlessly, a CMOS 16 bit cpu, some small number of TTL such as quad tristate latches etc but mainly the CPU, PROM, ram and analog parts life was hard in those days, the brilliant EE who designed that project was also sacked when he wouldnt release the project for billing as it ‘wasnt quite finished’ … after he was sacked, I lost interest in that company and resigned, too many brilliant EE’s I liked had been sacked as a mere assembly technician I was immune from being sacked unless I really made some stupid screwupsive sighs of relief from EE’s worldwide who’s jobs had just been saved in the nick of time but it was too late for lots of EE’s like ‘Ray X’ who had lost their first jobs because of 7400 seried TTL by comparison the National PACE job https://patents.google.com/patent/US4205230 worked flawlessly, a CMOS 16 bit cpu, some small number of TTL such as quad tristate latches etc but mainly the CPU, PROM, ram and analog parts life was hard in those days, the brilliant EE who designed that project was also sacked when he wouldnt release the project for billing as it ‘wasnt quite finished’ … after he was sacked, I lost interest in that company and resigned, too many brilliant EE’s I liked had been sacked as a mere assembly technician I was immune from being sacked unless I really made some stupid screwup