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Cosmac Microtutor

The Microtutor, manufactured in 1976, was used to educate engineers and others on how to program microprocessors. The unit is fully self-contained with the exception of the 9-volt power converter which plugs into the back of the unit. A clear plexiglass bottom allows the user to see all of the soldering done on the underside of the main board. The chips are all labelled both on the chip and on the board itself.

There are three slots in the back labelled M,P,E. The M slot (M for Memory) allows the insertion of a card containing 256 bytes of memory. The P slot (P for Processor) allows the insertion of a processor card (here RCA CDP1801). The third slot labelled 'E' is for expansion and allows the user to create custom cards for controlling other devices.

Microtutor is an 8-bit computer whose heart is the RCA CDP1801 microprocessor. It's made up of two plug-in ICs; the control IC and the register IC, both of which are mounted on the same plug-in card. RCA also proposed a CDP1802 which could handle more instructions than the 1801, and is on a single chip, but the basics of the 1801 and 1802 are the same. The control chip of the 1801 receives control signals from the clock and in turn controls the movemement of instructions and data through the register chip and into the RAM. There are 256 memory locations available in Microtutor although an 1801 can address up to 65,536 locations.

There are four control switches and eight data switches. Let's look at the four control switches: Clear, Start, Load, and In. The Clear button returns the microprocessor to the first instruction of your program and lets it sit there. The Start button begins execution of the program. The Load toggle switch is turned up when the program steps are entered and down when the program is to be run. The In button is pressed once for each instruction or data wword to be loaded. An instruction or data word is selected with the 8 "data" switches (these are toggles) and then In is pressed. Each press of In causes the instruction or data word to be entered into the next available memory location in the RAM. Also, as In is pressed, the values set on the data switches are displayed on the two digit LEDs.

One year later, in 1977, RCA released a Microtutor II system. It is basically the same computer but with a RCA CDP-1802 micro-processor integrated into the main board. Thus, no more "P" expansion slot, only "M" (for memory) and "E" (expansion) slots.

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Contributor: Paul H. Tarver (pictures & info)