DATAMATH

DATAMATH CALCULATOR MUSEUM

Sharp EL-204

Date of introduction:	October 1976	Display technology:	LED
New price:		Display size:	8
Size:	5.0" x 3.0" x 0.90" 128 x 75 x 23 mm³
Weight:	4.1 ounces, 117 grams	Serial No:	6311589Y
Batteries:	9V	Date of manufacture:	mth 11 year 1976
AC-Adapter:		Origin of manufacture:	Japan
Precision:	8	Integrated circuits:	TMS0956 (KGSΔ7642)
Memories:	1
Program steps:		Courtesy of:	Ken H. Meine
		Download manual:	(EU: 5.4M Bytes)

At first glance looks this early EL-204 calculator like a typical Sharp design of the Seventies but sports a red LED display instead the more common green Vacuum Fluorescent Display (VFD) known from many similar products of this timeframe.

Dismantling the featured EL-204 manufactured in November 1976 in Japan reveals a clean design based on a single-sided printed circuit board (PCB) for the main electronics and a double-sided PCB for the keyboard and powered by a disposable 9 Volts battery.

Removing the PCBs from the calculator housing divulges an unexpected surprise! The EL-204 makes use of a Texas Instruments TMS0956 single-chip calculator circuit based on the TMS1000 Microcomputer family. The TMS0950 architecture was introduced in 1975 with the TI-1200 and TI-1250 and soon replaced with the TMS0970, one of the most successful calculator chip designs.

While the TI-1250 uses a 6x4 layout of the keyboard, changed the EL-204 the layout into a 5x5 matrix adding the sqr(X) function. Reverse-engineering of the EL-204 calculator demonstrates that the TMS0956 actually is scanning a 7x4 keyboard matrix, a previously unknown feature of the TMS0950 series.

The display module manufactured by Sharp of the EL-204 uses nine small LED chips bonded on a substrate with an additional magnifying lens to enlarge the digits.

If you have additions to the above article please email: joerg@datamath.org.