Converting From 24-pin to 28-pin EPROMs ... and Back Again, by FR Wilk, June 2001
Converting DMEs is very simple and takes only minutes. Jumper, socket, new EPROM and your done.
The Change was made by BOSCH in late 1987 but is referred to as the 88 redesign. There is much confusion about the 1988 DME and much of it is nonsense. The memory size is the same as the 86 DME. In 1988, the 4k x 8 EPROM was replaced by a 8k x 8 EPROM. The 24-pin socket was replaced with a 28-pin socket. The final change was to add a jumper to the board that instructed the 8051 to ignore its internal 4k x 8 memory. All 8k x 8 of memory is now stored in the EPROM.
| Year | Internal 8051 ROM memory | External EPROM | Total |
| 1985.5-1987 | 4k x 8 | 4k x 8 | 8k x 8 |
| 1988-89 | 0 | 8k x 8 | 8k x 8 |
| 1988 DME | 1986 DME |
Jumper added |
No jumper |
28-pin socket |
24-pin socket |
Do not remove 24-pin socket. Simply add 4
single pins and your done. |
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| There is no need to remove the 28-pin socket just to install
a 24-pin socket. Simply do not use pins 1 & 2. This family of EPROMs (D2732 & D2764) were design to be able to do this. |
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The figure above-center shows a 2732 overlaid on a 2764 circuit. This printed circuit board (PCB) artwork shows pins 28, 27, and 26 of the 2764 connected. Provided the designer makes pin 26 of the 2764 hot, then the 2732 will have power just as BOSCH has here.
