PDP-8 Minicomputer code Using Intercept Jr. with Intersil IM6100 microprocessor

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Intersil IM6100 microprocessor

The Intercept Jr tutorial system is an interesting microcomputer trainer that can execute the PDP-8 minicomputer code.  The design uses the  Intersil IM6100 CMOS 12 bit microprocessor. The idea of using the old PDP-8 code turned out to be a poor idea in 1976 and the computer and the IM6100 were never very popular. The PDP-8 was introduced 11 years earlier in March 1965 and used a 12 bit word.  The PDP-8 had a limited instruction set when you compare it to computers and microprocessors available in 1976. Most computer users moved beyond the PDP-8 minicomputer in the mid 70's.

The idea of a low power CMOS PDP-8 simulator just did not have any legs and died rather quickly. The 16 bit minicomputers & microprocessors were coming out with good computing power and of course 32 and 64 bit microprocessors in a few years.

The Intersil Intercept is colorful and nice looking - a beautiful display in our museum along with a full set of manuals. Like a most of the microcomputer companies of the 70's they went our of business when IBM came along with the Personal Computer (PC) in 1981.  A few companies did hang on and some new ones tried to get in the market but IBM was just to strong and Apple is the only USA company in business today- IBM also eventually gave up the small personal computer market. Apple has had it ups and downs however now it is the largest company in the world even bigger then General Motors.

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Intersil Intercept Jr.

The Intercept consist of a main board with CPU, octal displays and a keyboard for entering instructions & data.  The board ( backplane or mainframe) has three sockets for the CPU card, RAM card & ROM card.

The IM6100 CMOS 12 bit microprocessor is a static device and can operate with a clock frequency from DC to 2 Mhz.  Military versions can operate at higher clock speeds.

Intersil Intercept Jr.

The serial interface provides the user with RS232 and 20 mA current loop interfaces.

Intersil Intercept Jr.

The CMOS is very low power and the computer can be operated with on board batteries - 4 D cells.

Intersil Intercept Jr.

The keyboard is a membrane type and the keys can enter a full instruction with one keystroke.

Intersil Intercept Jr.

The RAM module uses (12) 1024 x 1 IM6518 chips for 1 Kilobyte of 12 bit words. Battery holders to power the module are on the upper right of  the board.

Intersil Intercept Jr.

the ROM/PROM contains 256 to 2048 words of program depending on which chips are used. The CMOS board uses only about .75 watts of power.








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Intersil Intercept Jr.

This is readable when enlarged and summarizes the 6100 family of CMOS chips and the Intercept Jr.








Jon Titus gave me this update on PDP-8 clones a few days ago.
"Hi, Dave.

Fabri-Tek also manufactured a PDP-8 clone, the MP12.  You noted in an early blog that Fabri-Tek produced a lot of core-memory modules, so they must have decided to jump into the computer market, too.  You can find a copy of the Fabri-Tek manual here: http://bitsavers.trailing-edge.com/pdf/fabritek/402-1001-00_MP12refMan_1974.pdf. Even after many years, the MP12 op codes look very familiar."

David Larsen

This computer is really colorful and just a beautiful display. It is also functional however we don't have many operational computers in the museum. Just not time to do  this and volunteers are hard to find in our little Blue Ridge Mountain town of Floyd, Virginia. We do have several vintage gaming stations operational and they are very popular. 

           .^{"by David Larsen"  KK4WW Computer Collector Historian} 

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