Intel MG80386SX16 in a 88-pin PGA

Seeing this pin out, the first processor that comes to mind probably isn’t an Intel 80386.  The 80386DX came in a 132 pin package (PGA or QFP) and the 386SX came in a 100 pin QFP.  The 386SX was the low end version of the 386.  It made do with 16 bits of Data bus, and 24 bits of Address, as opposed to the full 32-bit buses of the DX.  This accounts for 27 less pins (16 Data + 7 Address, 2 data byte selects and a 16/32 bit pin).  That covers all but 6 of the difference in package sizes.  Where are the rest from?  As with most processors, the signaling pins are not the only pins used, or not used on a package.

The 80386DX has 84 signal pins, pins that carry information to or from the processor.  It also has 40 pins for power and ground.  In the early days, when processors had only 40 pins or less, it made sense, and was feasible to have a single power and ground for the entire chip.  As complexities increased, routing became harder, and it became easier to have multiple power and ground pins to the die.  Not to mention electrically more stable, as current requirements were also increasing.  In addition the 386DX has 8 pins not used at all.  These are known as ‘No Connects.’  They are reserved for future use, or were there for testing, or simply just not needed.

Intel 5962-9453301MXA MG80386SX16 – 16MHz 80386SX – 1996 Full Milspec

Moving to the 386SX, which has 26 less signal pins (58), the standard 100 pin package used 10 No Connects and the rest (32) for power and ground.  The pictured 386SX is a late production (1996) military spec processor in an 88 pin package.  88 pins still leave plenty (30 pins) for power, ground, and no connects.  The PGA 386SX was only produced for military/industrial uses.

Why use an expensive PGA package on a low end SX processor?  The reduced bus sizes were plenty for many industrial applications while the ceramic package was much more reliable, and mechanically strong when soldered on to a board then a plastic QFP.  The PGA could work over the entire military specification, for temperature, voltage etc.  Its likely the 386SX could run on an even smaller pin count, but the PGA88 package was a standard package already in production, which often dictates how many pins a processor will have.  The same is true today, pin-count is usually driven more by what works for the package, then what the processor actually strictly needs.

Raytheon KGV-25 – Click to Enlarge

Sometimes we get processors in on boards that are just too interesting, or too good looking to remove.  That is the case with this KGV-25 correlator board.  It is a processing systems used for decrypting communications that was in wide use by the US (and likely other) militaries in the 1990’s.  The KGV-25 could receive encrypted UHF data at rates of up to 400Mbps as part of the Multi-Mission Advanced Tactical Terminal (MATT). More information on the MATT can be found here on the FAS website.

As is typical of military equipment the system did not use the latest and greatest available at the time (this board is from 1994 so the Pentium era).  The board is run by a time proven and reliable Intel 80386 processor running at 25MHz. In addition to the MQ80386-25/B (MIL-STD-883B spec 386 processor) the board contains:
Intel MQ82380-20/B  – DMA Controller for interfacing with all the assorted SRAM on the board
Intel MQ82592/B – LAN Controller for interfacing with the rest of the system
VLSI VM05403 USART – Universal Asynch/Synch Receiver Transmitter
and on the back is a MQ80387-25/B Math-coprocessor for the 386 and 4MB of 35ns SRAM

Essentially a complete 80386 system, of similar performance to a higher end system int he late 1980’s.  Just with a lot more gold, and built to take a lot more abuse then your average beige box of the 80’s

In coin collecting often times an example is valued not because of its perfection, but because of its imperfections.  An off-center print, the obverse being printed upside down, or the double strike, where a coin doesn’t get cleared form the die and gets hit twice.

Such appears to be the case with this Intel A80386DX-33.  It clearly went through the engraver twice. A similar example (from the same exact lot) is fine, so clearly this one, made in early 1992, was a mistake that was not caught.  I have seen mis-aligned prints, off center etc, but this is the first example i have seen that was engraved twice.  It is interesting that even within the same lot, the spacing of the markings varied somewhat.  Notice that on the right side of the chips the sets of markings line up but they diverge towards the left.  It appears the stepper motors moving the tooling or the chips were a bit sloppy or out of calibration.

Have you seen any other double engraved comments? Let us know in the comments.