Texas Instruments CA-800 Cassette Interface (DVT Clear-Case)

Date of introduction:  Never
 (Announced: May 1982)
Display technology:  
New price:  MSRP: $60.00 Display size:  
Size:  6.5" x 3.2" x 1.3"
 165 x 82 x 33 mm3
Printer technology:   
Weight:  7.4 ounces, 210 grams Serial No:  ---
Batteries:  1*C Date of manufacture:  wk 52 year 1981
AC-Adapter:   Origin of manufacture:  USA (ATA)
Precision:   Integrated circuits:  TP0455/CD4511 or TP0456/CD4561, SN77203, LM393
Program steps:   Courtesy of:  Joerg Woerner

The CA-800 Cassette Interface allows to use most cassette audio recorders to save programs or data files on tape. It connects to the TI-88 Programmable through a 2-pin Peripheral I/O connector. A second Peripheral I/O connector on the back of the CA-800 allows to connect another device like the PC-800 Printer to the TI-88. The CA-800 is highly reliable because its redundant recording feature whereby information is stored twice no the tape.

The Operating System of the TI-88 supports four different types of tape recordings or tape files: 

Main memory file records all of calculator memory on tape
Program files from a minimum of eight program steps to all of program memory
Data files from a minimum of one data memory to all of data memory
Numbered Constant Memory Module (CRAM) records all contents of the module on tape

This CA-800 Clear-Case Prototype from a DVT (Design Validation Test) series manufactured most likely in December 1981 by Texas Instruments in their Abilene, TX facility was used by the engineering team at Texas Instruments to verify clearances between the electronics and the housing before introducing the EVT (Engineering Validation Test) series.

Dismantling this Cassette Interface Prototype reveals a rather complex design using a microcomputer of the TP0456 series and a SN77203 Voltage Controller chip together with some analog circuitry to connect to a tape recorder. The SN77203 is known from the TI-88 Schematics Diagram, it converts a single-cell battery (1.2 Volts - 1.5 Volts) to two independent power supplies, one adjustable for the LC-Display through a Serial I/O pin and one fixed for the main electronics. Due to the lower power consumption of its electronics is the battery life of the CA-800 projected to be 75 hours.

The TP0456 microcontroller sports Custom Design software CD4561, indicating that the original design was based on a TP0455 microcontroller with CD4511 software. The additional "D" marking indicates a very early production run of the chip.

Color-coded plugs of the CA-800 to cassette audio recorder:

Black wire to remote jack
Red wire to microphone jack
Grey wire to earphone jack


Don't connect a CA-800 Cassette Interface or a PC-800 Printer to TI-88 calculators without the Diode-Modification!


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If you have additions to the above article please email:

Joerg Woerner, December 22, 2020. No reprints without written permission.