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Texas Instruments introduced in 1973 with the TI-4000 Desktop calculator a very compact, yet capable product with a 12-digit display as an upgrade option to the TI-3000 and TI-3500 calculators with 8-digit resp. 10-digit displays. The TI-4000 was one of the first applications of TI’s TMS0200 Building Blocks for Desktop Calculators, a groundbreaking architecture centered around a Data Chip and various Support ICs:

• TMS0200 Data Chip – Register Processor with four 16-digit Registers and seven Keyboard Scan inputs • TMS0300 ROM Chip – 512*13 Bits Instruction Memory with serial interface to Data Chip and 13-digit display and keyboard scanning, up to 4 ROM Chips • TMC0400 ROM/Register Chip - 512*13 Bits Instruction Memory with parallel interface to ROM Chip and two 16-digit Registers • TMS0220 Printer Chip – Interface to two-color Drum Printer Mechanism • TMC0250 Printer/Display Chip – Interface to Thermal Printer Mechanism and Dot-Matrix Display

The TMS0200 Data Chip requires in a minimum configuration – as used in the TI-4000 – a TMS0300 ROM Chip for Program Memory and to scan up to 13 digits of the display.

While none of the known products based on the TMS0200 Building Blocks makes fully use of their possibilities like addressing up to 4 ROM chips and up to 16 Register Chips, did the design lay out the architecture of the TMS0500 Building Blocks for Scientific Calculators introduced with the "Slide Rule" calculator SR-50 in January 1974 and leading all the way to the legendary TI Programmable 59 and the amazing SR-60A Prompting Desktop calculator.

The TMC0500 Building Blocks were clearly designed with portable calculators in mind and optimized the necessary real estate of the "calculator brain" dramatically:

• TMS0200 - Minimum configuration: 40-pin Data Chip + 40-pin ROM Chip + 16-pin Segment Decoder, optional ROM Expansion with 40-pin ROM/Register Chip • TMC0500 - Minimum configuration: 28-pin Arithmetic Chip + 28-pin Scanning ROM Chip, optional ROM Expansion with piggy-backing a second Scanning ROM Chip and/or additional 8-pin Bare ROM Chips

The similarity between the TMC0500 and TMS0200 architecture allowed even the introduction of additional TMC02xx devices used with products based on the TMC0500 Building Blocks for Scientific and Programmable calculators like the TMC0251 Printer Chip for Thermal Printer Mechanism applied with the Printer Cradle PC-100 for the SR-51, SR-52 and SR-56 calculators.

One pin labeled "PFS" selects on these Chips for Thermal Printers and Dot-Matrix Displays how the 13-bit Instruction Word is provided from the ROM:

• TMS0200 Mode (n.c.): IRG A Input for B0 – B5 and IRG B Input for B6 – B12 • TMC0500 Mode (VDD): IRG B Input for B0 – B12

The TMC0250 was designed to interface products based on the TMC0500 Building Blocks for Scientific and Programmable calculators with Texas Instruments’ Thermal Printhead EPN3100 used for example with the PC-100 Printer Cradle and SR-60 Prompting calculator. The EPN3100 comprises a linear array of 100 heaters arranged in 20 characters of five columns, each. A stepper motor moves the thermal paper seven consecutive steps to print characters in a 7*5 dot matrix font but even allows printing graphs by addressing the every dot per print line individually.

The TMC0250 uses the following signals to interface with its electronics:

• Twenty Digit Driver Outputs D1 – D20 for the 20 characters of five columns, each • Five Column Drivers Outputs C1 – C5 for the 5 columns per character • Four Motor Driver Outputs A, /A, B, and /B to advance the thermal printer paper with a Four-Phase stepper motor

The interface between either the TMS0200 Data Chip or TMC501/TMC0501E Arithmetic Chips and the TMC0250 uses a pin-count optimized approach with just 6 or 7 wires:

• IRG B for TMC0501/TMC0501E Arithmetic Chips or IRG A and IRG B for the TMS0200 Data Chip to receive instructions • 6-bit Function Data containing to designate one of 64 characters to be printed in each of the 20 positions per line is transmitted serially through the EXT Input • The BUSY Output of the TMC0250 Printer Chip connects with the corresponding input of the TMS0200 Data Chip or TMC0501/TMC0501E Arithmetic Chips to synchronize the components • IDLE, PHI 1 and PHI 2 Signals are used to synchronize all peripherals connected to the TMC501/TMC0501E Arithmetic Chips with the 16 States of its Instruction Cycle

A special programming of the TMC0250 allows to replace the EPN3100 Thermal Printhead with a 20-character 5*7 LED dot matrix display used with the Prompting calculators SR-60 and SR-60A. While the TMC0251, TMC0254, TMC0255 Printer Chips advances the thermal paper in small increments with a Four-Phase stepper motor, replaces the TMC0253 Display Chip the stepper motor with a simple external shift register cycling through the seven rows of the LED display:

Printer Chips:

• Print first row of 20 characters • Advance stepper motor to next row and print it • Repeat until last row is printed • Pause until next line of characters is loaded

Display Chips:

• Scan first row of 20 characters • Advance shift register to next row and scan it • Repeat until last row is scanned • Repeat scanning display until next line of characters is loaded

With only a few designs based on the TMS0200 Building Blocks for Desktop Calculators or TMC0500 Building Blocks for Scientific and Programmable Calculators using the optional TMC0250 Printer/Display Chip and Texas Instruments numbering them in a sequential way, we can easily track the individual designs.

QUICK-LINK to TMS0200 Family
QUICK-LINK to TMS0500 Family.

Type	Calculators	Function
TMC0251	PC-100, PC-100A, PC-100B, PC-100C	Thermal Dot-Matrix Printer 20 Digits, 5*7 Characters
TMC0253	SR-60, SR-60A	Dot-Matrix LED Display 20 Digits, 5*7 Characters
TMC0254	SR-60, SR-60A	Thermal Dot-Matrix Printer 20 Digits, 5*7 Characters
TMC0255	TI-5230	Thermal Dot-Matrix Printer 20 Digits, 5*7 Characters

Parameter	Min	Typ	Max	Unit	Comments
VSS	+9.2	+10.0	+10.6	V
VDD		0		V
VGG	-7.2	-7.0	-6.4	V
PHI1, PHI2	50	250	300	kHz	Opposite phases

Pin	IO	Function	Pin	IO	Function
1	O	Digit Driver 1 (LSD)	40	V	VGG (-7 V)
2	O	Digit Driver 2	39	V	VDD (0 V)
3	O	Digit Driver 3	38	I	Clock Input 1
4	O	Digit Driver 4	37	I	Clock Input 2
5	O	Digit Driver 5	36	O	Busy with Printer
6	O	Digit Driver 6	35	I	Function Data
7	O	Digit Driver 7	34	I	IDLE
8	O	Digit Driver 8	33	I	Program Format Select
9	O	Digit Driver 9	32	I	Instruction word B6-B12/B0-B12
10	O	Digit Driver 10	31	O	Stepper Motor Phase /A
11	O	Digit Driver 11	30	O	Stepper Motor Phase A/CLK
12	O	Digit Driver 12	29	O	Stepper Motor Phase B/IN B
13	O	Digit Driver 13	28	O	Stepper Motor Phase /B
14	O	Digit Driver 14	27	I	Instruction word B0-B5/n.c.
15	O	Digit Driver 15	26	I	Column Driver 5 (left)
16	O	Digit Driver 16	25	O	Column Driver 4
17	O	Digit Driver 17	24	O	Column Driver 3
18	O	Digit Driver 18	23	O	Column Driver 2
19	O	Digit Driver 19	22	O	Column Driver 1 (right)
20	O	Digit Driver 20 (MSD)	21	V	VSS (+10 V)

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

© Joerg Woerner, March 11, 2021. No reprints without written permission.