Texas Instruments TP0470/TP0475/TP0480/TP0485

• Features

Understanding that sooner or later the complete portfolio of electronic calculators and educational products needs to be ported from power-hungry LED- and VF-Displays to LC-Displays, Texas Instruments initiated in 1978 together with the development of the TI Programmable 59 successor, dubbed "Project X", a very ambitious project called "LCD III". Main objective of this project was the replacement of all existing calculator chips used within the broad spectrum of basic four-function calculators to high-end programmable calculators and educational toys with a family of just three chip sizes A, B, and C, differing mainly in ROM and RAM capacity and each chip optionally including additional modules for timekeeping functions and drivers for LC-Displays.

Looking into the advantages and disadvantages of the two architectures in use, Register Processors and Digit Processors, and already experienced with porting the TMS1000 microcontroller-based TI-30 calculator chip TMC0980 to CMOS technology for the TI-50 resulting in the TP0320 chip, Texas Instruments decided to combine the speed of Register Processors with the flexibility of Digit Processors with introducing not only a so-called Fast-ROM with 13-bit width to the normal instructions ROM but switching from a metal gate CMOS process to a more advanced polysilicon gate CMOS process.

The chips were defined as follows:

• Chip A replaces TMC1000, TMC0970, TMC1990, TMC0920, TP0310
• Chip B replaces TMC0980, TMC1980, TMC1100, TP0320
• Chip C replaces TMC1500

Each chip was meant to be more powerful than the chip it replaces with Chip B a subset of Chip C and Chip A a subset of Chip B.

History tells us the Texas Instruments did not meet these demanding goals and the only application of an LCD III chip is the TP0485 used with the cancelled TI Programmable 88 calculator. However did the work on LCD III influence future calculator chips, the TP0455/TP0456 design inherited the optional chip-to-chip communication with a 4-bit I/O port and the optional module for timekeeping functions while the TP0458 design made use of the scalability of ROM and RAM capacity.

The polysilicon gate CMOS process had a great comeback with the TMC70C20 8-bit single-chip microcontroller family used with the Compact Computer 40 and many other TI Consumer Products.

The TP0470/TP0475/TP0480/TP0485 chip includes 41,600 Bits Read-Only Memory (ROM 3k*13 Bits, Fast ROM 128*13 Bits) and 1,408 Bits Random-Access Memory (RAM, 22 Registers * 16 digits), a 4-bit Arithmetic unit, timekeeping functionality with a 32.768 kHz crystal (TP0475/TP0485 only), an high-speed oscillator for a 1.6 MHz Master Clock, a 4-bit I/O bus for processor-to-processor communication and external memory expansion, an 1-bit I/O bus for calculator-to-calculator or calculator-to-peripheral communication, a programmable PLA for segment decoding and both segment and digit multiplexing for a 12-digit LC-Display with up to 84 segments and 4 common scan lines (TP0480/TP0485 only). A newly developed feature allowed most pins to be assigned either Input or Output functionality to allow easy “piggy backing” of multiple TP0485 chips communicating through the 4-bit I/O bus including a 4-wire handshake protocol.

Early iterations of the TI Programmable 88 called "Product 225 - TI-85" used three LCD III chips the final design consolidated into two chips packaged in different sized housings with the larger CD2901 chip responsible for Timekeeping, Keyscan, and I/O and the smaller CD2902 chip interfacing with external memory and providing the Learn mode. A similar approach could be found with the Primary-Secondary architecture introduced with the TI-55-II based on two TP0455/TP0456 chips. 

• Family Members and Applications

Type Calculator/Product Application Comments
TP0470/CD2902 Product 225 - TI-85
(November, 1979)
Programmable ROM code CD2902, Primary Controller
TP0470/CD2903 Product 225 - TI-85
(November 23, 1979)
Programmable ROM code CD2903, Arithmentic Controller
TP0475/CD2901 Product 225 - TI-85
(November 23, 1979,
February 1, 1980)
Programmable ROM code CD2901, Timekeeping, Keyscan, I/O Controller
TP0475/CD2902 Product 225 - TI-85
(February 1, 1980)
Programmable ROM code CD2902, Primary Controller
TP0485/CD2901 Product 225 - TI-88
(March 12, 1980)
Programmable ROM code CD2901, Timekeeping, Keyscan, I/O Controller
TP0485/CD2902 Product 225 - TI-88
(March 12, 1980)
Programmable ROM code CD2902, Primary Controller


• Architecture

  Description Comments
Architecture Single-chip Calculator Scientific, Programmable
Category Digit Processor 4-bit digits
ROM Size 41,600 Bits 3072 Words * 13 Bits +
128 Words * 13 Bits Fast RP<
RAM Size 1,408 Bits 22 Registers * 16 digits
64 Bits Display Register?
Outputs 4 Common, 21 Segments Integrated Common Scan Line and Segment Drivers
(not used with TI-88)
Inputs 5 Keyboard Segment to Keyboard Scan-Matrix
Miscellaneous 4-bit I/O Port, 4-wire Handshake
1-bit I/O Port
32.768 kHz Timekeeping
High-speed Clock
MCU-to-MCU, MCU to ext. Memory
External Crystal
1.6 MHz Master Clock

• Technical Specifications

Item Min Typ Max Unit Comments
VCC   3.0   V   
GND   0   V   
CK   1,600   kHz  Internal oscillator       

• Technology

The TP0470/TP0475/TP0485 were manufactured in a 5 um silicon gate CMOS process (metal width = 0.20 mil / 5.0 um, metal spacing = 0.20 mil / 5.0 um, diffusion width = 0.20 mil / 5.0 um, diffusion spacing = 0.20 mil / 5.0 um).

The die size of the TP0485 is approximately 220 mils * 220 mils / 5.6 mm * 5.6 mm.

• Packaging

The TP0470/TP0475/TP0485 uses either a 0.6” wide 40-pin SPDIP (Plastic Dual In-line Package with a 0.07” / 1.778 mm lead pitch)
or a 0.4” wide 28-pin SPDIP (Shrink Plastic Dual In-line Package with a 0.07” / 1.778 mm lead pitch).

• Pin Configuration

TP0485/CD2901 (TI Programmable 88)

Pin IO Function Pin IO Function
1 I OSC-IN 32.768 kHz 40 IO IO1
2 O OSC-OUT 32.768 kHz 39 IO IO2
3 O OSC-TP  8.192 kHz 38 IO IO8
4 O R29 (Piezo) 37 IO IO8
5 O R28 Key row 9 36 O R15 Data to P
6 I KE Key input 3 35 I KH Low Battery Indicator
7 O R1 Key row 2 34 O R9 Interrupt
8 O R4 Key row 3 33 I KF Ready
9 I KC Key input 2 32 O R10 Request
10 O R12 Key row 5 31 I KG Request
11 O R8 Key row 4 30 O R11 Ready
12 I KD Key input 4, OFF 29 O R2 Display Data
13 O R20 Key row 7 28 O R6 Display Clock
14 O R24 Key row 8 27 IO PIO Data from Peripheral
15 I KA Key input 5, ON 26 O R3 Display Control
16 O R16 Key row 6 25   n.c.
17 O R0 Key row 1 24   n.c.
18 I KB Key input 1 23 I Test-CLK (GND)
19 V VCC Positive Voltage 22 O HS-CLK 1.6 MHz Out
20 V GND Ground 21 I TEST (GND)

TP0485/CD2902 (TI Programmable 88)

Pin IO Function Pin IO Function
1 O R0 CS0 28 IO IO1
2 O R2 CS2 27 IO IO2
3 O R3 CS3 26 IO IO8
4 O R7 CS7 25 IO IO8
5 O Do not connect 24 I Do not connect
6 O R5 CS5 23 O Do not connect
7 O R4 CS4 22 I Do not connect
8 I KA Interrupt 21 O R1 CS1
9 O R14 Ready 20 O R6 CS6
10 I KB Request 19 O Do not connect
11 O R15 Request 18 O LS-CLK 267 kHz Out
12 I KE Ready 17 I Test-CLK (GND)
13 V VCC Positive Voltage 16 I HS-CLK 1.6 MHz In
14 V GND Ground 15 I TEST (GND)

• Keyboard Scan-Matrix

The keyboard of the TI Programmable 88 consist of an x/y-matrix connected to 9 R-Outputs and the keymatrix inputs KA, KB, KC, KD, and KE. A 3-Position (momentary-locking-momentary) slide switch connects ON and OFF to keymatrix inputs KA and KD respectively. 

Example for the TI Programmable 88 with TP0485/CD2901:

R1 EQN EVAL # OP 2nd
R12 GTO EE ( ) ÷
R16 7 8 0 ×
R20 4 5 6
R24 R/S 1 2 3 +
R28 CE/C 0 . +/− =

• Display

Calculators based on the TP0485 could make use of 12-digit LCDs (Liquid-Crystal-Displays) with 4 COM (common scan) lines but the TI Programmable 88 didn't make use of the internal display drivers and used two TP0530 cascadable display drivers, instead. 

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If you have additions to the above datasheet please email:

© Sean Riddle and Joerg Woerner, January 14, 2021. No reprints without written permission.