Signetics Military 8X305 – 1990 (8550201YA)

Some time ago we talked about the history of the Signetics 8X300 line of processors.  Originally released as the SMS300 in 1975 by SMS, the design was bought by Signetics.  It was a fairly unique 8-bit bipolar design, running at 8MHz. Its focus was signals processing, long before dedicated DSP’s such as the TI TMS320 came about.  The design was updated in 1982 to add some additional instructions and data handling.

Since it excelled so well at signals processing, the design worked well for military applications, where signals processing was of great use (interpreting data from a host of, usually, RF sensors.  The 8X305 was made in the normal 50 pin DIP, a 68 pin LCC, and an unusual 52 pin flat pack for military use.  In the 52-pin package the extra 2 pins are simply ‘No Connects’. (In the 68 pin version the extra 18 pins are divided amongst extra VCC, VR, GND, and N/C).

For military applications the greatest importance is on reliability.  This takes the form of three main areas:

Mechanical: How well can the design handle shocks, and vibrations, usually this is handled through better bonding wires, and more rigid package specs/inspection.
Electrical: How well can the device tolerate not great electrical conditions, higher reliability is achieved when the device can operate with a voltage that may very up to 10%, rather then the 5% or less commercial devices are designed to.
Temperature:  This is closely related to mechanical, as temperature stability requires the package to be damaged by expansion/contraction in wild temperature swings.  Obviously the silicon die itself needs to work with the same electrical characteristics at different ends of the temp range.  Many electrical parameters (such as resistance, and biasing) change over temperature, so the device must handle this. Typical military spec is -55C-125C (-67F-257F).  A range of 180C, from well below freezing, to well above boiling.

Venus – From the Mariner 10 Probe

This Signetics 8X305 (Drawing # 8550201YA) is rated at -55-125C at 5V +/- 10% running at 8MHz.  It meets all the mechanical/inspection and testing requirements of MIL-STD-883 Class B.  This type of design work is well understood, and now a days, rather routine.  Making electronics work at 125C is no longer an engineering feat.  But then, what if we need more? Lots more.

Recently NASA contracted with Ozark Integrated Circuits to do just that.  NASA wants a process kit for IC’s that will run happily at 500C (932F) . At this temperature lead and tin have melted, and aluminum isn’t even very solid. If that sounds a bit inhospitable, you’d be right, and its exactly the conditions NASA faces with designing a rover for use on our nearest neighbor, Venus.

Ozark previously created such a process good for up to 350C, but thats still not hot enough for Venus.  Ozark is using a silicon carbide substrate, and some other proprietary methods.  They will not actually produce the chips for NASA, but rather licenses the methods to do so to a foundry service of NASA’s choosing, who will then manufacture and test them.

Surface of Venus, from Venera-13

In the upper atmosphere, temps are below 0, and at the surface, atmospheric pressure is 90 times greater than on earth, another challenge for making a chip, with a die recessed in a sealed cavity.  Such requirements, and the technology to meet it, will greatly enhance our exploration abilities, and no doubt, trickle down in some way, to the electronics we use each day.

On November 20th, 1969 a small company was formed in Mountain View, CA called Scientific Micro Systems Inc (SMS). They would join the dozens of post-Fairchild semiconductor startups in Silicon Valley.  Many of these we remember and know well, Intel, AMD, Zilog, MOS all are familiar and have designed processors that left a story, if not a legacy, in history. SMS has became a forgotten player in the roaring 70’s but they did introduce a few important things to the market. First 4096-bit bipolar Schottky ROM? SMS. First 256-bit bipolar Schottky RAM? Again SMS.

Signetics N8X300I – Early 1978

In January 1975 SMS announced prototypes of their own 8-bit microcontroller.  The SMS300 was a non-traditional design.  It focused on manipulation of signals.  It had 16-bit instructions, but operated on data 8 bits at a time.  It had very limited ways of accessing external memory (and no real way to access data memory).  It was designed as perhaps the first DSP.  It was fabricated in bipolar Schottky transistor technology.  This allowed it to be incredibly fast (albeit very power hungry) for its time.  Initial clock speeds were 6.66MHz and quickly ramped to 8MHz in 1976.  The SMS300 was initially not available for sale as a single chip.  It was sold as a single board computer called the SMS330 (as well as the SMS331 and SMS332) which contained everything needed to run the SMS300.  This was packaged like a oversized 64pin DIP (similar to how some of the BASIC Stamp microntrollers are today). These systems started at $370 and topped out at $1460.  In August of 1975 SMS ‘unbundled’ the SMS300 and began selling it (and its support chips) separately to those who wanted them.

Soviet Electronika KM1818VM01A 8X300 Clone

SMS did not make the SMS300 themselves, they contracted another Silicon Valley company to fabricate them.  Signetics, founded in 1961 by ex-Fairchild workers, was the first company founded to solely manufacture ICs rather then discrete transistors.  In 1975 Signetics was purchased by Philips but continued to operate under the Signetics trademark until 1993. Signetics made all of the SMS300 devices for SMS, and in 1976 Signetics became a second-source, and could sell the SMS300 under the Signetics brand.  By 1978 Signetics had purchased the rights to the SMS300 and renamed it the 8X300.  1977 or 1978 is generally when people think the 8X300 was develped. This is, unfortunately, due to forgotten history as by the time Signetcs bought the design, it had been on the market and in use for over 2 years.  Signetics continued to make the 8X300 into the early 1990s where it found wide use in disk controllers, telecommunications and other DSP like environments.  The N8X300 was also second sourced by AMD though I have yet to see one.  The 8X300 was also *second sourced* by the Soviets in the 80’s and early 90’s by the Electronika state electronics company in what is now Voronezh, Russia.  These of course were not licensed copies but they are however, still of interest.

Signetics N8X305N Early 1988

In around 1982 Signetics released the N8X305, the successor to the 8X300.  It was functionally compatible but increased the general purpose registers to 13 from 8 among some other instruction improvements that greatly improved upon the data handling deficiencies of the 8X300. Processor speed was also boosted to 10MHz. (200ns instruction time vs 250ns for the 8X300) The N8X305 also used the same pin-out as the 8X300 and the same 50pin DIP package (as well as adding a 68pin PLCC).  AMD second-sourced the 305 as the AM29X305.  The N8X305 continued to be made into the 1990s and saw use in many military applications as well.  Because of this Signetics/Philips could not simply terminate production.  They sold production rights to Lansdale Semiconductor Inc., who still offers the N8X305 to this day.

Signetics N8X401I – 1988

In 1986 Signetics again revised the design and released the N8X401.  This processor now had a full 32 instruction (including a RETURN instruction allowing the use of subroutines) The N8X401 also added an 8-bit data bus making data handling somewhat simpler but also increasing the package size to a 64 pin DIP.  Internal usable registers was increased to 16 and the instruction width was increased to 20-bits. Clock speed remained at 10MHz but it was now fabricated in ECL (Emitter Coupled Logic).  This among other improvements, helped to result in a 35% speed boost over the N8X305.

AMD AM29X305DC – N8X305 Second Source – 1985

The N8X401 was not a great success, primarily because of the competition at the time.  By 1986 8-bits, even for a DSP, was rapidly becoming out of date, especially with such purpose built DSPs such as the Motorola DSP56000 and the industry standard setting TI TMS320 series.

Thus is the story of one of the most odd processors to come out of the chip boom of the 1970’s (EA 9002, MMI 6701, AMI S2000 et al).  There are several other forgotten processors of that era which are also deserving of some remembrance.  In time we’ll try to document their history here at the CPU Shack as well.