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[June 30, 2003]
6th :Improved 16MB(EDO type) board.
This 6th article is about the improved 16MB board.
As shown on previous articles (for referring), there had been a problem such as undesirable automatic-writing-reaction to the FD (Floppy Disk) even when reading contents from FD.
It have been solved by an AND-gate IC with which generate *OE from *UCAS and *LCAS.
Memory chips and additional IC.
The name of chips I used in this case is KM416V4104B (by SAMSUNG). It is same type memory as 65165. (So you can also use 65165.)
The AND-gate IC is a 74HC08 which containes four gates in its package. This has not so fast response, but it is enough for the purpose.
Selecting location of the AND-gate IC is important, because the total thickness of memory board will affect the floating gap from the main board. (Thinner is better, of course.)
The location between two memory chips may be the best as the IC's position, because the total length of wiring will be shorter than other place. And total thickness can be decreased by sinking the IC.
Wiring diagram.
The left picture is a wiring diagram of the improved 16MB board.
Because different *UCAS, *LCAS and *OE lines are supplied to each chips from the connector, two AND gates were used.
(Other lines such as A0, A1, A10 and A11 are used for both chips.)
After work.
At this time, I have coated wires with home-use varnish for fixing. Though it is convenient, some trouble may occur.
In my case, abnormal phenomenon on the PC (mouse could not be moved) had been observed. I think that very thin film of varnish might coat surface of the connector's pins.
Frequent operations (insert/remove the board to the connector) may tear off the coating.
I have cleared the trouble by such method.
Go to other articles.
Preface Page, 1st:8MB(FP), 2nd:16MB(EDO), 3rd:16MB(FP), 4th:32MB(EDO), 5th:another 32MB(EDO)
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The left picture is a wiring diagram of the improved 16MB board.