I am interested in finding old microprocessor development systems, including hardware, manuals, and related materials. If you have any such equipment or documentation, please send me an e-mail!

The CPU at the heart of the Instructor 50 is the Signetics 2650. The following description appeared in the October 1975 issue of IEEE Spectrum magazine:

Multiprocessor eliminates need for special input/output, memory, or other interfaces devices

This microprocessor can reduce or eliminate problems associated with interface, according to the manufacturer. Program memory may also be reduced.

The n-channel device, designated the 2650, requires a single +5 volt power supply and is completely TTL compatible on all input/output pins, including the single-phase TTL clock output. The interface structure of the 2650 eliminates the need for external level shifters, pull-up resistors, and and/or latches, when connected to other TTL or NMOS devices.

The processor has a basic bus architecture with an 8-bit bidirectional data bus and a separate 15-bit address bus. The fixed instruction set includes 75 arithmetic, logical, branch, and control instructions. The processor has seven general-purpose registers, a main arithmetic logic unit and a separate address adder, and eight-level return address stack, and a BCD arithmetic capability.

Three input/output modes are provided, including a two-byte parallel mode, a single-byte parallel mode, and a unique serial input/output mode using the flag and sense lines. The serial mode is powerful in minimal system configurations since it provides a means of performing serial computations under program control.

As a result, a low-cost interface can be designed for communicating with teletype and other serial input devices without memory buffering or reformatting the data. The 2650 also has a hardware vectored interrupt capability that can handle up to 64 different I/O devices.

The device has been designed using static logic only. Therefore, the clock can be stopped in its low state for indefinite periods of time without any loss of status or data currently on the chip.

The introductory price of the 2650 is $165 in single-unit quantities and under $100 for quantities exceeding 1000 units.

Contact Signetics, 811 East Arques Ave., Sunnyvale, Calif. 94086.

This advertisement appeared in the January 1979 issue of IEEE Spectrum magazine.

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Last updated January 28, 2006