Potential hardware problem with RamFast

[DO11@calvacom.fr (Dominique OTTELLO)]

Hello from France.

I apologize for my bad English. I hope you'll understand me.

It seems it can have hardware design problems with RamFast. At least with
mine. It is a short card Rev D.

On this card there is three kinds of logical circuits : LS, HC and HCT.

With 5 volts power supply:
The minimum output logical one level for TTL LS is 2.4 volts
The minimum input  logical one level for MOS HC is 3.5 volts
The inputs of HCT circuits are fully compatible with outputs of TLL LS.

If there is connection between TTL LS outpout and MOS HC input, the logical
level one of the TTL LS can be not seeing as one by the MOS HC.

It is very difficult to lay hands on this problem because I don't have
schematics of the card.

I have had this problem with electronic computer on Aircraft and the
manufacturer wrote a Service Bulletin that ask airlines to replace MOS HC
circuits by MOS HCT circuits.

May be there is no potential problem with the RamFast if there is no
connection between LS outputs and HC inputs.

Thank you for your attention.


* Dominique Ottello   -   do11�calvacom.fr    ! Sysop of Apple IIGS city on *
* Paris - France - Apple II's user since 1980 ! Calvacom-RCI network        *