Regular-speed TTL parts were also available for a time in the 6400 series – these had an extended industrial temperature range of −40 °C to +85 °C. While companies such as Mullard listed 6400-series compatible parts in 1970 data sheets, by 1973 there was no mention of the 6400 family in the Texas Instruments TTL Data Book.
Normal-hastigheds TTL kredsløb var også tilgængelig for en tid via 6400-serien – disse kan klare et bredere industri temperaturinterval på −40 °C til +85 °C. Selvom firmaer såsom Mullard listede 6400-seriens kompatible kredsløb i 1970 databladene, var der ingen omtale om 6400-serien i 1973 i Texas Instruments TTL Data Book.