Motorola MC6802

A few months ago I looked at a Motorola MC6800 bought on eBay that was branded with a Freescale logo, contained an Hitachi fabricated die (probably from late 80’s or early 90’s) and had a 2016 assembly date code.  Reader Jeremy wanted to compare a real vintage 6800 and kindly ordered this MC6802 for me.

I can make out from the very worn and faded markings

MC6802L  P1H852

Which I believe is a week 52 1978 assembly date code. Released in 1977 as an upgrade to the MC6800, offering an internal oscillator and 128 Bytes of RAM.


Thus assembled almost exactly 39 years ago prior to the date of this this post. It is a truly vintage part, packaged in a ceramic DIP.  I popped the lid off using a blowtorch to melt the solder. I also used a strong magnet to pull the lid off (To avoid damaging the die.)The die is soldered to the lead frame, one interesting feature the ground wire has two bond wires, one going to the die, another to the lead frame, but rather than bonding directly to the gold plated lead frame it is bonded to very small piece of silicon or metal – I can’t see why they did that.As it is in the package I am able to take a die photo with the bond wires intact.  The package depth limits me to the 10x objective for the die photo.  The working distance of my high magnification objectives is too small to focus on the die in-situ. To zoom in on the features I had to remove the die from the package.

MC6802 Die PhotoMC6802 Die Photo

(click on image for high resolution version)

Back in 1978 3″ silicon wafers was state of the art.  With a die size of 5.55mm x 4.96mm I calculate they would have had 99 candidate die per wafer.  They were probably doing well to yield 25-30 die per wafer at the time. The datasheet also mentions an MC6808 which was identical to the 6802 but without the 128 Byte RAM, so they obviously recovered some failed parts where just the RAM was defective to gross more parts per wafer.

The die has a distinctive and unusual monochrome look to it.  I removed the die (By heating the package on a hotplate and carefully sliding the die off of the solder. Which proved tricky to do with a very hot die and without a jig holding the die still.

You can see the pitted/mottled texture of the oxide layers which is obscuring the poly and active areas. The latter can be tricky to see in some structures.Normally the oxides are transparent (It is effectively glass), since this was sealed in a ceramic package, it must have come out of the wafer fab looking like this.  I have seen this once before on another old Motorola part.  So clearly it is a characteristic of the process Motorola used. It’s unfortunate for us as it makes viewing the structures quite difficult.

The main die logo is very visible confirming this is pucker Motorola MC6802MC6802 Die Logo

Not so visible, hidden under the mottled dielectrics there is another die mark R1H.  Could that be Ray Hirt sneaking his initials onto the chip (He is one of the designers referred to on the MC6800 Wiki page) or is R1H for something else?

MC6802 Layout

One aspect of taking the die photo in-situ is that it makes identifying the pin-out much easier.  Here is the die photo with pin-out labelled.MC6802 pin-outYou can see the internal oscillator pins on the the top left side.  T he ROM that contains the instruction set on the left, the data input pins at the top, and the output pins bottom and right sides.

MC6802 Memory


There’s a 2kBytes (16kb) large ROM on the chip. A NOR type ROM programmed with a masked (depletion) implant.  Comparing this image to a reference I found online and it is clear

(Attribution unsure found in lecture published on-line, original maybe slide set “Digital Integrated Circuits” by Rabaey et al ©2003)

(Static) RAM


The 128 Byte (1kb) RAM is also interesting. The datasheet mentions that 32 Bytes of RAM are retainable and this is clearly the smaller section on the left. I can trace the Vcc line of that section to the Vcc/Standby pin. (The larger right side goes to the main Vcc pin.)



















Counting out the bits, (the small retainable section in one half is 16Bytes or 128bits, so this image contains 4 bits (Or 4 SRAM cells)In part because it is difficult to see the active area and use of buried contacts I cannot figure out the circuit used.  Given this is an NMOS process I suspect it is a resistive load SRAM cell like this one, but I am unable to reverse engineer it from the layout (Without removing the metal).

MC6802 Process

I mentioned buried contacts, or more correctly buried poly contacts.  These are contacts between polysilicon and substrate, used extensively on this part. In a CMOS process you would not find them.  Here is an example of two such contacts on the die

Some commentary about the process quality you can  observe. In 1978 the metal lines would have been wet etched (Likely in a buffered phosphoric acid mixture). Given that the etch quality of the Aluminum tracks appears very good to meYou can see a tiny amount of notching sometimes where the metal line crosses a poly line, and there is slight mis-alignment of metal to contacts, and the metal lines look a little small for the size of the contacts.  But overall though this looks like a good quality process for 1978.

Finally many thanks again to Jeremy for supplying the part, and merry christmas to all of you who celebrate it.

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HCF4007U Dual Complementary Pair plus Inverter

Integrated circuits do not get any simpler than this. This is an HCF4007U made by ST with a week 27 1993 date code

ST HCF4007UAccording to the datasheet it can be, depending on the pin connections, either 3 inverters, a 3 input NOR or a 3 input NAND gate.

De-capping and you can see it is just 6 transistors! on a 1.47 mm x 1.35 mm die.ST HCF4007U die photo

(click on image for high resolution version)

It is barely an integrated circuit. Even with my lack of skills I can reverse engineer this part


And the pin-out





There is one mystery to me. The part is definitely CMOS as the datasheet specifies it, so they must be polysilicon gate MOSFETs.  Yet if you look at this high magnification image of a transistor edge, I cannot see the polysilicon??

Thanks to Jeremy for providing the part.

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Maxim 785 Power Supply Controller

Another chip from the clamshell iBook from 2000.  Another Maxim power chip, this time it is from the main PCB.


Its a MAX785C which I am pretty sure is a dual (3.3V & 5V) PWM buck regulator for laptop computers.



I could not find a datasheet for the MAX785 but I did find one for the MAX786 which as you will see is almost certainly a minor change, or a slightly different version of the MAX785.

Here is the 4.6 mm x 2.8 mm dieMAX785 Die Photo (click on image for high resolution version)

For the MAX786 Maxim were once again kind enough to publish a chip topography 🙂 and you can see it matches the MAX785 die photo and pad layoutHere is my MAX785 die photo with the pads annotated, you can clearly see the symmetrical and  identical 3.3V & 5V PWM supply blocks with the 3.3V on the left.

Looking at the transistors zoomed in I can see a single Aluminum layer with 5 μm gate lengths and two polysilicon layers.

Referring to the Maxim Reliability Report I found whilst researching the earlier Maxim chip I can say with confidence the MAX785 was made on the Maxim SG5 process that looks something like this  (The transistors here are pretty drawn pretty ugly IMO)Its a CMOS process with a PNP transistor, zener diode and a Chrome/Si precision resistors. I have annotated the previous image with the layersThe layer 2 (PNP base drive) is/was unusual, they are making vertical PNP transistors.  In a standard CMOS process you can build lateral PNP transistors using the regular process.  However the gain of the lateral transistor is normally very low (As the base is defined lithographically you cannot make the base very narrow, unlike a diffused vertical base.)  Here is a large Bipolar transistor on this chip which is sandwiched between an two arrays of them to make  high current drive transistors.

Most of the large output transistors in the PWM blocks are I believe multi-finger MOSFET devices, here is a zoom image of one of them (It s hard to see the polysilicon gate as they have stitched metal lines along the gate, you can see the single gate contact at the very bottom right of the image.)


Update:  Laser trimmed resistors?

Frank commented that he could see some laser trimmed resistors, this was a very eagle eye observation! A bit of background, most silicon resistors are made with polysilicon or diffusions, and there are a number of variables that limit their accuracy such as thickness, width, dopant concentration, amount of dopant electrically activated during thermal processing.  It is typical that a resistor value is at best +/-10%.  For this reason most designs require only differential or ratio accuracy, and here the variables cancel out and you get very accurate matching.  Well over 90% (Perhaps 99%) of analog ic’s make do with these resistors. Occasionally a design needs an accurate absolute resistor, for these, a few processes (Like this Maxim SG5 process) offer a precision thin film resistor. These are made from thin (Typically 20nm-100nm) metal layer like Chrome used here.  I believe they can be made with +/-1-2 % accuracy. Sometimes a design needs even more absolute accuracy and for that they laser trim the thin film resistors, using a high power laser to ablate the metal track usually on a probe station where they measure the desired signal before and after trimming.

This is the section of the die where the thin film resistors have been cut.

It is a very complex serpentine that enables a wide variation in resistor value depending on where cuts are made.  After staring at this a bit and thinking some more, I don’t think they are laser trim cuts. The cut material looks too clean for laser ablation. What I think has happened is they designed the part with a un-cut serpentine resistor,  and then evaluated the initial prototypes making various laser cuts, and then used the results to change the resistor mask. In high volume, this would be much cheaper than trimming every die on a probe station.

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Texas Instruments TL494C PWM Control Circuit

The TL494C is a pulse width modulation control circuit, designed for power supply control, from the small power board on a clamshell iBook from 2000.

I have read the datasheet a few times and find it a quite complicated device.  I think is used to regulate the load when charging the battery, but I’m not very sure of that.

From the datasheet which was first published in January 1983 and revised March 2017, a 34 year old active document (And active part) that has to be some sort of record!

Onto the die photo which is really nice 🙂
TL494C die photo(As always click on image for high resolution version)

The die size is 2.08 mm x 1.9 mm (3.95 mm2) another single metal Bipolar process.


From this diagram in the datasheet I was able to identify the pins.  The output transistors are obvious and I can see the error amplifiers and some of the other functional blocks



Here is my annotated die photo

There are some interesting devices on this chip, look at this 6 terminal beast in the error amplifier – unfortunately I have no idea what it is.

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