33 Keyboard

This document provides a general description and the principles of operation for the Teletype Corporation 33 keyboard, as of September 1971. It covers both nonparity and parity electromechanical models, which are used to generate ASCII characters.

Key details include:

• Functional Overview: The 33 keyboard functions as an electromechanical device where pressing a key moves a codebar mechanism. This movement is translated into a parallel electrical output, which is then converted by a distributor mechanism into a serial start-stop signal for transmission.
• Nonparity vs. Parity: The primary difference between models is the eighth-level pulse. Nonparity keyboards always transmit a marking eighth pulse, while parity keyboards adjust this pulse to ensure an even number of marking pulses per character.
• Mechanical Operation: The document details the codebar mechanism, noting that the combination of slotted and solid bars acts as both the encoding system and an interlock to prevent multiple keys from being pressed simultaneously.
• Safety and Maintenance: The document includes a caution to disconnect all power before inspection and specifies operating environment requirements (40°F to 110°F).
• Operational Features: It describes the "universal codebar mechanism," which triggers the distributor clutch and incorporates a non-repeat lever to prevent the machine from continuously transmitting if a key is held down.