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

Function of the card:
SDTDL 2-2 w plus a plus o w/load

Saturated Drift Transistor Diode Logic (SDTDL) is a form of Diode-transistor logic using faster drift-field transistors.

Part number: 372240

Customer Eng reference number: 734322

PCB number: 484959

Used in: IBM 2821 Control Unit

Symbol:+O, +A

+O: Positive OR. In-phase output is positive if one or more input signals are positive. Out-of phase output is negative for the above condition.

+A: Positive AND. in-phase output is positive only when all inputs are positive. Out-of-phase output is negative for the above condition.
IBM SMS card type AXR 372240 IBM SMS card type AXR 372240

Image courtesy of Roberto Gonzalez Rocha

References: IBM 2821 CCD, p31
This page created by Ken Shirriff on Wed Sep 15 18:15:11 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.