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Texas Instruments TMC0595 Magnetic I/O Chip

• Features

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, CLK 1 and CLK 2 Outputs 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 -VB (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 -VB and using external preamplifiers for the track signals while reading magnetic cards.

QUICK-LINK to TMS0500 Family.

• Applications

SR-52, SR-52A

• Revisions

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

• Technical Specifications

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

• Packaging

The TMC0595 uses a standard 0.4” wide 22-pin DIP (Dual In-line Package with a 0.1” / 2.54 mm lead pitch).

• Pin Configuration

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


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

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