This page describes the IBM SMS card "CEH", and is part of the SMS card database.

Function of the card:
CTDL-Inverter Latch NPN

Listed in 1401 SMS card usage

Complemented Transistor Diode Logic (CTDL) is IBM's term for a form of diode-transistor logic.

Part number: 370139

PCB number: 493331

Used in: IBM 1401

IBM SMS card type CEH 370139 IBM SMS card type CEH 370139 IBM SMS card type CEH 370139

Image courtesy of Henk Stegeman

References: Coslet data
1_2 SMS Cards, p79
This page created by Ken Shirriff on Wed Sep 15 18:15:10 2021.

The information on these pages comes from a variety of sources, especially old IBM documents on, as well as information from the IBM 1401 restoration team, especially Tim Coslet's SMS data and Jim Hunt's data. Much of this information was obtained through OCR, so don't expect complete accuracy. These pages are not associated with IBM in any way.