Motorola MC6847P Video Display Generator

Used in the TRS-80, Acorn Atom and several other home computers the MC6847P is a video display generator enabling a TV to be used to display text and graphics. The date code is week 52 1978. (YMCA by the village people have just made #1 ūüėČ ) It’s a 40 pin package and is a very big chunk of plastic (52mm x 14mm) compared to modern chips.Motorola MC6847P

Die Photo

Die size is  4.86 mm x 5.13 mm (24.9mm2) a fairly large die for 1978.MC6847 Die Photo

click on image for higher resolution version

The die photo has a very black and white feel, with the layers under the metal very obscured. I have seen this before, here and here.  It is clearly a characteristic of the Motorola process at the time. The poly is just visible and the active area diffusions are fully obscured. Was it deliberate or just a symptom of the process tools they used for deposition? I have a theory that it might have been deliberately done to reduce reflections from poly layers and thus improve metal lithography. Only an ex-Motorola process engineer would know.


The MC6847P datasheet is easy to find, I attach a copy here.  It even has its own wikipedia entry. The MC6847P  (P was for plastic package) interfaced the MC6800 CPU to a colour or black and white NTSC television.


Only capable of rendering 256 x 192 dots,  thats only 49,152 pixels!


I extracted the pin-out from the datasheet and die photo.   Notice there 41 bonds pads with 40 pins.  There are two Vss (Ground) bond pads one on either side of the die.

The character generator ROM is easy to spot. I think the area below the ROM is the parallel to serial shift register as per this block diagram


The Motorola MC6847P was made on the same 5őľm NMOS process as the MC6800 MCU. ¬†Buoyed by my success in removing the metal in the recent ITT 41116 I thought I would also have a try here. ¬†So I bought out the Armour Etch again together with HCl to etch the Aluminum. ¬†Overall the result is not too bad – here is a die photo of the poly layerMC6847 poly die photo

click on image for higher resolution version

The poly lines and the active area diffusions are now clearly visible   The field oxide has not been uniformly removed with lots of residual oxide around.  If I try to remove all this oxide residue I will likely attack and lift the polysilicon lines.

Now comparing the ROM area (Both images taken with 20x objective)

You can see how the ROM is programed with active area.  The pair of vertical polysilicon lines cross an irregular grid.  The inside of the grid lines is field oxide. Where the field oxide has been removed the polysilicon is crossing active area, so a transistor is formed.

This image shows transistors in the shift register area imaged with my 80x objectiveThe tips of the polysilicon gates terminate on the field oxide islands.  You can also see the contacts to the diffusion (to make source and drain connections) and to the polysilicon.  Also in all the contacts you can see little black dots,  this is silicon that has precipitated out of the Aluminum metal during processing.  A small amount of silicon (~1%) was typically added to Aluminum to improve the electro migration resistance of the tracks.


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One Response to Motorola MC6847P Video Display Generator

  1. Jeremy says:

    Been waiting for this one! ūüôā Thanks

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