Electronics > Beginners
EPROM pin replacement compatibility questions
analogix:
I'm looking to replace a 2732 EPROM with a 27512 and similarly a 2764 replaced with a 27010 (or the equivalent EEPROMs). The additional pins of the larger chips will be used for 16x bank-switching via a 4-way DIP switch.
Since the other pins are more or less pin-pin compatible it appears I can just use a "through socket" for them and only re-route the additional ones (which will extend past the existing EPROM sockets anyway).
I've seen a photo of a similar adapter PCB (2732 to 27512) which only plugs into the topmost 4 pins of the 27512 (pins 1, 2, 27 and 28) but this puzzles me since pin 26 of the 27512 (A13) goes to pin 24 of the 2732 (Vcc). The other pins' signals match.
Can this work (A13 goes to Vcc)?
For the 2764 to 27010 things become more complicated as several of the 2764's pins have different signals, so I'll need to reroute multiple pins.
rhodges:
Yes, you can have A13 also be Vcc. But instead of having 16 pages, you will only get 8. Page 0 will load from page 2, page 1 from 3, and so on. Because A13 is always high.
analogix:
Aha! Thanks for clearing that up.
I should have thought of that myself, because it's logic high and lows for the 4 highest address pins that are used to select different memory banks of the EPROM, right?
The confusing thing is that according to the photo of the adapter PCB (which gave me the idea to build something similar mysef) it allows for 16 banks. The poster in the forum where I found it also confirms that it's used to replace a 2732. How can this be? And the picture appears to show only the
Unfortunately I've been unable to get in touch with the poster for a more detailed photo and additional info.
That aside, for my own adapter I'm thinking the best solution would be to have a "through" pin socket for the 2732 (or 2764), then offset the new EPROM (27512 or 27010) to the left or right of it and reroute the signals appropriately. And to lower costs I could go for a single adapter PCB with solder-jumper-pads to allow for a 2732-27512 or a 2764-27010 configuration. Would this be a good solution, or are there better ways to do it?
analogix:
I think I've more or less worked out a PCB design for this (see attachement below and disregard the newbie design layout :) ).
I still don't understand how that other adapter in the photo I posted earlier can have A13 connected to VCC and still allow for 16 banks as the photo says, so in my design I've offset two sets of IC sockets, joining and separating each pin as needed.
The bottom-most socket (silk-screen marked 2764/2732) is a "through socket" and plugs into where the 2732/2764 EPROMs used to be while the topmost socket (silk-screened as a 32-pin socket) houses the 27512 or 27010 for 16 banks worth of data.
A solder-pad jumper is used so that the same PCB can be used for either a 2732/27512 combo or 2764/27010 combo.
Unless I've made any mistakes there are only two things I haven't figured out yet:
1) VPP: pin 1 of the 2764 and pin 1 of the 27010 is for the VPP signal. I'm not completely sure what it is, but from the datasheets it appears to have something to do with the programing voltage. Can these pins be disconnected (as they are now, perhaps even disconnected from each other)?
2) I'm aiming for a rotary type 16-way DIP switch for ease of use. Actually the board will have an option for an internal (on-board) DIP switch or an external type (also rotary, but with a longer shaft similar to a potmeter with a knob on) with a jumper to choose one or the other.
But how do I know which switch combination corresponds to a particular bank selection/address?
To avoid confusion it would be great to have DIP switch setting 1 to correspond with the lowest address EPROM bank while setting 16 would correspond to the highest and final bank in the 27512/27010 EPROM. I can't find any info on this in the various EPROM datasheets -does anyone have info on this they can share here?
soldar:
Just in case it is of any interest to readers of this thread, I just posted this in the sales department:
--- Quote from: soldar on August 19, 2019, 11:36:33 am --- EEPROM UV Erasable for sale
I have the following lying around:
QTY 3 of TMS2516JDL
QTY 1 of TMS2532
QTY 12 of HN482764G
QTY 2 of HN4827128G-25
The lot offered for 0.01 Eur (one euro cent), as is, where is, without any guarantee. Buyer pays shipping, postage, and any and all incidental expenses such as, but not limited to, beer, etc.
--- End quote ---
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