DATAMATH CALCULATOR MUSEUM
The TI Programmable 88 calculator is powered by the BP88 battery pack containing one AA-size rechargeable NiCd cell. The electronics of the TI-88 is centered around the TP0485 Microcontroller family manufactured in a polysilicon gate CMOS process powered with 3 Volts while the drivers for the alphanumeric LC-Display with sixteen characters require an additional negative -4 Volts supply.
The SN77203 Display Interface Voltage Controller Chip integrates the following functional blocks:
• 1-cell to 3 Volts step-up DC/DC converter with internal reference voltage generation
• 1-cell to -4 Volts inverting DC/DC converter with digital On/Off control input
• Low Battery Indicator with digital status output
• Driver circuit for bidirectional serial calculator-to-calculator or calculator-to-peripheral communication
The SN77203 is highly integrated and requires only 4 external components for its application in the TI-88:
• 20 uH inductor for step-up DC/DC converter
• 300 uH inductor inverting DC/DC converter
• 1N4148 catch diode for inverting DC/DC converter
• 330 nF filter capacitor for internal voltage reference
TI Programmable 88 Calculator, CA-800 Cassette Interface, PC-800 Printer
|VDISP||-4.0||V||Activated with CONTROL Input|
|LBI||0.9||V||Active 0.9 V, Hysteresis 0.2 V|
The SN77203 is manufactured in a 7.5 um metal gate Bipolar process (metal width = 0.3 mil / 7.5 um, metal spacing = 0.3 mil / 7.5 um, diffusion width = 0.3 mil / 7.5 um, diffusion spacing = 0.5 mil / 12.0 um).
The die size of the SN77203 is approximately 120 mils * 65 mils / 3.0 mm * 1.7 mm.
The SN77203 uses a 0.3” wide 14-pin DIP (Dual In-line Package with a 0.1” / 2.54 mm lead pitch).
|1||V||VBAT1 (1.5 V In)||14||I||CONTROL (VDISP on/off)|
|2||V||VBAT2 (1.5 V In)||13||V||L2 (to GND)|
|3||V||L1 (to VBAT1)||12||V||VREF (C to GND)|
|4||V||GND||11||O||LBI (Low Battery Ind.)|
|5||V||VCC (+3.0 V Out)||10||V||VDISP (-4.0 V Out)|
|6||V||VBUFF (+3.0 V Out)||9||I||R (SI/O from TP0485)|
|7||IO||SI/O (Peripheral Bus)||8||O||K (SI/O to TP0485)|
If you have additions to the above datasheet please email: email@example.com.
© Sean Riddle and oerg Woerner, January 22, 2021. No reprints
without written permission.