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Re: Using a 27C512 for a 27C256?

"Alan P. Biddle" writes:
 > There is a trick for using a 27C512 as two 27C256 chips, which you can
 > select (manually) with a pin.  I don't have the pinouts handy, and wonder if
 > you can use a 27C512 as a 27C256 directly, using only half of it of course.
 > Murphy being Murphy, I need a 27C256, have many 27C512s, and it is a holiday
 > weekend.  :)

Write your 27C256 image in the '512 in the lower half. Or the upper 
half. Or better yet write it twice once in the bottom and once in the 
top just for good measure. Don't lie to the programer and claim the 512 
is really a 256, even if the programer allows such tales.

Then when you insert the 27C512 in the 27C256 socket you want to bend
the pin for the high address line out of the socket. Short it to either
VCC or GND. Is best to use a 10k to 47k resistor as the pull up/down. I
*think* the high address line is on pin 1 so a pullup to VCC is easy, 1
to 28. Using a 47k resistor soldered to these pins will probably not
affect the chip in your EPROM programer.

David Kelly N4HHE, dkelly@hiwaay.net
The human mind ordinarily operates at only ten percent of its
capacity -- the rest is overhead for the operating system.

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