The 2816 family of EEPROMs, in 24-pin packages, take /WE on pin 21. This is address
line A11 on S4. We cannot reconfigure this pin to function properly as a write line
in hardware, and as a result no 2816s are listed in S4's device library. These devices
can, however, be handled as 2817's, which are identical in most respects. The 2817
is in a 28-pin package with /WE on pin 27. Pin 23, which corresponds to pin 21 of
a 24-pin package, is no connect.
A simple adapter is required, consisting of 2 stacked sockets. In the following
diagram, the outer 2 columns represent the lower, 28 pin socket, and the inner columns
the upper, 24 pin socket. The sockets are positioned such that their ground pins
(pin 12 upper, pin 14 lower) are aligned. All pins are common except pins 21 upper
(23 lower) and 24 upper (26 lower), which should not be mated and can be cut off
the lower socket. Pin 21 upper is jumpered to pin 27 lower, and pin 24 upper is
jumpered to pin 28 lower, as shown.
If a 2816 is placed in the upper socket, the whole assembly will program as a 2817.
The algorithm for the same manufacturer's 2817 will normally be suitable, and should
be selected in the first instance. Refer to the manufacturer's data book for further
guidance.
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