Texas Instruments SR-60A

This Texas Instruments SR-60A programmable desktop calculator was introduced early in 1977 and succeeds the SR-60. At first glance the SR-60A seems to be an SR-60 with a factory installed memory expansion, the base model could hold 1920 program steps and 100 memory registers. A second memory expansion was available as an option. The huge printed circuit board (PCB) with a total of 27 TMC0599 RAM chips was mounted below the keyboard next to the Main PCB. A fully-optioned SR-60 could hold programs with a maximum of 5760 steps and 430 memory registers.

Dismantling the SR-60A is not an easy task but is worth the trouble. Removing the upper part of the housing allows access to a rather complex assembly installed in the bottom shell of the calculator. You'll notice immediately the huge power supply, magnetic card reader, thermal dot-matrix printer, alphanumeric display with 20 characters but you'll miss the calculator brain. It takes another four screws to remove the keyboard and reveal the processor architecture of this high-end programmable desktop calculator.

The SR-60A is based on the TMC0500 building blocks developed already in 1974 and introduced with the SR-50. The architecture used at least two Integrated Circuits (ICs) with the TMC0501E EnhancedArithmetic Chip and the TMC0520 SCOM (Scanning Read Only Memory) Chip, but was expandable to a maximum of 8 SCOMs, additional RAM as program memory for programmable calculators, additional RAM for general purpose registers and even dedicated chips driving a printer or display. Most scientific and programmable calculators from Texas Instruments between 1974 and 1982 like the SR-51, SR-52 and TI-58 are based on these chips. Please find all known calculators using the TMC0500 architecture here.

Exploring the Integrated Circuits (ICs) located in this SR-60A introduced in 1977 reveals a design very similar to the TI-59 / PC-100C combination.

Main PCB:

The Main PCB is mounted below the full-size keyboard and accommodates the processing system of the SR-60A desktop calculator. All the peripheral devices, e.g. the keyboard, alphanumeric display, thermal dot-matrix printer, and magnetic card reader are connected to the Main PCB. Additional connectors are available for the different memory expansion modules available. The calculator brain is centered around the TMC0501E Enhanced Arithmetic Chip and three TMC0580 DSCOMs Double Scanning Read Only Memory, marked TMC0582, TMC0583 and TMC0584, respectively. There are five TMC0599 Multi-Register Chips soldered on the Main PCB of the SR-60A, we know the “piggy back” approach to reduce the real estate on the PCB already from the SR-52.

The TMC0599 RAM (Randon Access Memory) chips contain 1920 Bits of read/write memory, each, combining a total of 480 program steps and 40 memory registers on the Main PCB of the SR-60A.
Both the SCOMs and RAMs communicate on serial bus lines with the TMC0501E Arithmetic chip, this reduced the pin count of the Integrated Circuits dramatically and allows an easy expansion of the architecture. This serial bus system is used for communication with the display, printer and card reader controllers, too.

Compared with the SR-52 handheld programmable calculator based on the TMC0500 building blocks, the Main PCB of the SR-60A looks very crowded. We assume that most of the small- and medium scale CMOS devices are used as glue logic to connect the keyboard, buffer the serial buses and other housekeeping purposes.

Memory expansion – Option 1:

We know this memory expansion already as an option for the SR-60 to increase the internal memory of the calculator from 480 program steps and 40 memory registers to 1920 program steps and 100 memory registers. The expansion is implemented with just two small, identical daughter boards holding 5 resp. 3 TMC0599 RAM chips. They are accessible through a bottom panel in the housing for easy installation.

We assume that all SR-60A calculators were delivered with the Option 1 factory installed.

Memory expansion – Option 2:

The second memory expansion, a huge printed circuit board (PCB) with a total of 27 TMC0599 RAM chips, was mounted as a factory installed option below the keyboard next to the Main PCB. A fully-optioned SR-60A could hold programs with a maximum of 5760 steps and 430 memory registers.

Keyboard:

The SR-60A programmable desktop calculator is a very capable machine with a whole set of scientific functions built in, and all are directly accessible with the full size, 95 key keyboard.

Display:

The display subsystem uses 20 individual 5x7 dot-matrix LED display units, each with its own SN27882 row driver, discrete column drivers and a TMC0253 Printer/Display Chip to time-multiplex the 700 LEDs of the assembly. The TMC0253 is connected with the above mentioned serial bus to the TMC0501E Arithmetic Chip.

Printer:

The SR-60A provides a thermal dot-matrix printer that can print up to 20 alphanumeric characters in a line formed by a 5x7 dot matrix pattern. The printer mechanism is very similar with the ones located in the PC-100 printer cradle and TI-5230 desktop calculator and uses the same print head. The electronics of the SR-60A printer is centered around a TMC0250 Printer/Display Chip with a TMC0254 part designation, variations of this chip named TMC0251 and TMC0255 were located in the PC-100 resp. TI-5230. The TMC0254 is connected with the serial bus to the TMC0501E Arithmetic Chip.

Card Reader:

The SR-60A provides an integrated magnetic card reader for saving and loading both programs and data. The magnetic cards are 10½" by 2" (267 mm * 51 mm) in size and not compatible with the SR-52 and TI-59. Each side of the magnetic cards store 480 program steps or 60 data registers. The electronics of the card reader is centered around a TMC0596 chip, we know the TMC0594 and TMC0595 from the SR-52 resp. TI-59 calculators. The TMC0596 Magnetic I/O chip is connected with the serial bus to the TMC0501E Arithmetic Chip.

Power Supply:

The power supply of the SR-60A uses a switch to select between 105V - 130V AC or 198V – 265V AC line voltage. The power consumption is specified with max. 40 VA.

In 1977 the SR-60A was priced $995, a TI-59 / PC-100C combination with similar performance cost about $500. The introduction of the Apple II in June 1977, the Commodore CBM and Tandy TRS-80 series end of 1977 marked the start of the Personal Computer era and the SR-60 / SR-60A was discontinued in 1979. Logically they are today rare collector items!

Don't miss the related TI-5230.

Price list (United States):

Please find below list prices of some SR-60A accessories provided by fellow collector Bill Figueroa. Thanks!

Fellow collectors - if you own a Texas Instruments SR-60A calculator ,  please report us the serial number and date code from the back of the calculator for our Database.

Find here an excerpt from the Texas Instruments Incorporated bulletin CL-354 dated 1978:

SR-60 / SR-60A  Database