Montgomery Ward P8F aka TXI-8644A

Date of introduction:  August 1, 1973 Display technology:  LED-modules + lens
New price:  $59.50 Display size:  8
Size:  5.7" x 3.1" x 1.6"
 146 x 79 x 41 mm3
Weight:  5.1 ounces, 144 grams Serial No:  37X-0002843
Batteries:  4*AA Date of manufacture:  
AC-Adapter:   Origin of manufacture:  USA
Precision:  8 Integrated circuits:  TMS0103
Program steps:   Courtesy of:  Joo Oliveira

TXI-8644A_Back.jpg (215340 Byte)This neat calculator does not look like a Texas Instruments product. To identify it, you have to know more about the coding used by Montgomery Ward:

Models starting with

TXI were produced by Texas Instruments
DAN were produced by APF
DNS were produced by National Semiconductors (later Novus)
GLE by Lloyd's

An identical housing was used for both the P8P alias TXI-8645A and the P8M alias TXI-8646A calculators. The printed circuit board and the serial number of the calculator gives you another information: Late P8F calculators (e.g. 37X-0026077 from Thomas Brockmeier) carry a PCB with a marking P8F/P8P. Okay, the same PCB in two calculators. Please compare this serial number with the P8P: 37X-0066692. Let's assume that the P8P replaced the P8F in the year 1974 and the happy customer got the %-key for free.

Dismantling this P8F reveals another surprise: The printed circuit board (PCB) carries a magic number that links to a lot of other calculators like the Radio Shack EC-300 and EC-1000.

The printed circuit board of the P8F looks like most calculator based on the TMS0100 single-chip calculator circuit. Just a LED-display, some driver circuits and a DC/DC-converter to generate the power supply.
More important is the number etched in the PCB:
TXI-8644A_PCB.jpg (65902 Byte)
The small display board uses LED-modules with just one digit per module. Once again the magic number:
TXI-8644A_DSP1.jpg (24505 Byte)
The components side of the display board sports the logo of Texas Instruments etched in the PCB:
13-04-709-xxx numbers were used by TI !
TXI-8644A_DSP.jpg (19337 Byte)

This calculator looks very unfamiliar compared to other Texas Instruments calculators. Notice the combined [-=] and [+=] keys not known from calculators sold by TI.

Don't miss the rare TXI-8661A based on the Exactra 23 calculator.

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If you have additions to the above article please email:

Joerg Woerner, December 5, 2001. No reprints without written permission.