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The Tektronix 21 and Tektronix 31 are programmable desktop calculators. They feature a complete set of transcendental functions. The 21 supports simple programs (sequences of keystrokes) whereas the 31 supports conditional branching and subroutines. Data can be stored on the magnetic tape cartridge, for example, the 020-0082-00.

Several interfaces were available:

These connect to the calculator through a 50-pin card-edge bus interface supporting DMA access at up to 125 kbyte/s. The bus uses open-collector TTL drivers and can be daisy-chained through multiple peripherals (which all have two matching bus connectors for this purpose). It must be terminated at the last unit.

The 31/10 Graphic Calculator System was a bundle of a model 31 with a 4010-1 graphics terminal, interface and software collection.


Documents Referencing 31

Document Class Title Authors Year Links
Tekscope 1974 V6 N3.pdf Article The 31/53 Calculator-based Measurement Instrumentation Package John Mulvey 1974


The 21 and 31 are built around a custom LSI chip set, the 156-0243-00 Adder-Subtracter, 156-0238-00 Working Register Storage, 156-0239-00/156-0240-00/156-0242-00 Function Decoding, 156-0235-00 Microcode Routine Address ROM, 156-0231-00 through 156-0234-00 Microcode ROM/Next Address Latch, 156-0237-00 Timing and Constant Storage ROM, 156-0236-00 K Register Storage and 156-0241-00 A & C Operation Control ROM. These chips were manufactured by American Microsystems, Inc. as full custom parts.