Re: Unitron EPROM Writer UPDATE

["Mark Cummings" <NOTfigjams@primus.com.au>]

> I just sat down with the Unitron to help answer some questions, and have
> immediately hit a wall.  Although I took a digital design course back in
> university, little of it stayed with me!  I'm left not being able to
figure
> out how the pins are numbered.  If you could briefly explain it, I will
> continue the study of this board.

ahh, very easy. there is a notched end on each chip, usually a half moon,
but sometimes just a dot in a corner.

If you orientate the chip so that the notch is leftmost the pin numbering
starts from the bottom-left as #1 then anti-clockwise around the chips
highest pin # in the top left. The printing on the chip is also normally the
right orientation in the above description.

For example if you look at the scanned image of the front of the board you
did, the 2716 EPROM is upside down to most other chips on the board, and pin
1 would be the bottom right in that scan, counting up to 24 in the bottom
left.

Power is normally the highest pin number, but not always, and Earth is
normally the diagonally opposite corner. Power and Earth often have larger
tracks on the board too.

BTW the numbering for the ZIF is assuming there is a 28pin EPROM in it, pin
1 is near the lever. But in the case of all EPROM burners that use a 28pin
ZIF for 24 and 28pin EPROMs when you use a 24 pin EPROM, pin 1 of that EPROM
goes into pin 3 of the socket, so for the orientation of you ZIF the EPROMs
would have the top 4 pins empty. The explanation for this becomes more
obvious if you compare pinouts for 24 and 28pin EPROMs. A tip so you dont
forget is to draw a line on the ZIF socket from the middle of pin 2 and 3
across to the middle of pin 26 and 27.

The pin numbering for surface mount is whole other story.

HTH,

Mark