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Texas Instruments announced on September 16, 1975 with the SR-52 their first Keystroke Programmable Handheld Calculator based on the TMC0500 Building Blocks for Scientific and Programmable Calculators introduced already in January 1974 with the SR-50 “Slide Rule” calculator. While the SR-50 used only the minimum configuration of this groundbreaking architecture combining the TMC0501 Arithmetic Chip and one TMC0521 SCOM (Scanning Read-Only Memory) Chip with the necessary display drivers for its 14-digit LED display plus power supply and clock generation, went the SR-52 a step ahead and made full use of the TMC0500 Building Blocks. A closer look at the PCB (printed circuit board) of the SR-52 reveals a total of seven PMOS (P-channel Metal–oxide Semiconductor) chips:

• TMC0501: Arithmetic Chip – Register Processor with five 16-digit Registers and segment decoder/driver • TMC0524: TMC0520 Scanning and Read-Only Memory Chip – 1,024*13 Bits Instruction Memory with serial interface to Arithmetic Chip, 16 Constants with 16 digits, each, two 16-digit Registers and 16-digit display scanning • TMC0562, TMC0563: Two TMC0560 Bare Read-Only Memory Chips – 1,024*13 Bits Instruction Memory with serial interface to Arithmetic Chip, each for a combined 3,072*13 Bits Instruction Memory • TMC0595: Magnetic I/O Chip – Four channel interface for magnetic card reader to save and load programs with up to 224 steps • TMC0599*2: Two Multi-Register Chips – 240*8 Bits Random Access Memory with 4-bit I/O Bus to Arithmetic Chip, stores 240 program steps or 30 numbers of 16 digits, each

Texas Instruments introduced together with the calculator a matching "Printer Cradle" PC-100 with an integrated alphanumerical printer capable to print up to 20 characters per line at a speed of three lines per second on a 2.5 inch wide thermal paper. The SR-52 calculator connects to the PC-100 printer cradle with a 12-pin connector accessible through its battery compartment and featuring all TMC0500 signals necessary to communicate to two additional PMOS chips hosted on the PC-100 PCB:

• TMC0561, TMC0569: Two TMC0560 Bare Read-Only Memory Chips – 1,024*13 Bits Instruction Memory with serial interface to Arithmetic Chip for all commands responsible for printing and tracing • TMC0251: TMC0250 Printer/Display Chip – Interface to Thermal Printer Mechanism

The SR-60 Prompting Desktop calculator introduced in 1976 took the architecture of the SR-52 even a step further and integrated an alphanumeric display and keyboard with even more Instruction and Data/program memory into a large but elegant housing.

The TMC0595 Magnetic I/O Chip provides the interface between the four-track magnetic card read/write mechanism and the TMC0501 Arithmetic Chip. Communication between the two chips is realized with multiple means:

• IDLE, PHI 1 and PHI 2 Signals are used to synchronize all peripherals connected to the TMC0501 Arithmetic Chip with the 16 States of its Instruction Cycle • EXT Output indicates that the TMC0501 Arithmetic Chip is addressing external memories/registers • IRG Input to receive the 13-bit Instruction Words from the Instruction Memory

The TMC0595 Magnetic I/O Chip also conditions the signals to and from the magnetic card read/write mechanism (e.g. motor, card sensor input, channel 1-4) to make them compatible with PMOS logic levels.

The card speed of the SR-52 is set at 3.8 IPS (inches per second), the calculator will function at a card speed of 3.3 IPS to 4.3 IPS. At any speed below 3.3 IPS, the magnetic head can’t generate the required voltage to drive the TMC0595 Magnetic I/O Chip. At any speed above 4.3 IPS, the write length exceeds the usable length of the card.

In the TMC0595 Magnetic I/O Chip, to read and write properly, the reference voltage -V_B (Pin 18) must be maintained within a tight tolerance:

• TMC0595 Rev B: -VB = -5.1V ± 5% • TMC0595 Rev C: -VB = -3.3V ± 5% • TMC0595 Rev D: -VB = -VBAT

The TMC0595 Magnetic I/O Chip was replaced in 1977 with the TMC0594 Magnetic I/O Chip dropping the tight tolerances of the reference voltage -V_B and using external preamplifiers for the track signals while reading magnetic cards.

QUICK-LINK to TMS0500 Family.

Revision	Products	First Prototypes	Comments
TMC0595	SR-52		Initial design Reference Voltage -5.1 V
TMC0595 Rev A	SR-52		Reference Voltage -5.1 V
TMC0595 Rev B	SR-52	March 1975	Reference Voltage -5.1 V
TMC0595 Rev C	SR-52, SR-60	April 1975	Reference Voltage -3.3 V
TMC0595 Rev D	SR-52A	July 1975	Reference Voltage -VBAT
TMC0595 Rev E	SR-52 II (TI-59)	October 1976	External Amplifier Renamed to TMC0594

Item	Min	Typ	Max	Unit	Comments
VSS		0		V
VR	-4.3	-3.75	-3.3	V	Revision D
VDD	-10.5	-10.0	-9.5	V
VGG	-16.3	-15.8	-15.3	V
PHI1, PHI2		225	230	kHz	Opposite phases

Pin	IO	Function	Pin	IO	Function
1	A	R/W Track 2	22	A	R/W Track 3
2	A	Capacitor Track 2	21	A	Capacitor Track 3
3	A	R/W Track 1	20	A	R/WTrack 4
4	A	Capacitor Track 1	19	A	Capacitor Track 4
5	V	Common Voltage	18	V	Reference Voltage
6	O	Instruction words	17	V	Common Voltage
7	I	Calculating status	16	I	External access
8	O	Keyboard emulation	15	I	Clock Input 2
9	O	Motor on/off	14	I	Clock Input 1
10	I	Card Sensing Input	13	V	Negative Voltage VDD
11	O	Lamp (not connected)	12	V	Negative Voltage VGG

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

© Joerg Woerner, February 02, 2001. No reprints without written permission.