Date : Sun, 31 Aug 2008 01:23:47 +0100
From : jumbos.bazzar@... (Mark Haysman)
Subject: FRAM....
Aha...gotcha! Damn 2MHz and it's timing.....
So...being a fan of diodes, and a loather of piggybacking, I tried rigging
it like this:
On the FRAM, break the connection between pin 20 of the chip and the socket.
Pull pin 20 of the chip low with a 4k7 and connect two diode (1N4148)
cathodes to it. Connect the anode of one to pin 20 of the socket, and the
other anode to pin 22. Thus creating an OR gate validating pin 20 with pin
22, which has the 2MHz bus signal encoded in it.
Working a charm now for me too - altho still would like to use it for a bit
to be sure of reliability. Thx for the info! Those few discreets should be
able to go underboard as well, making for a neat layout.
Mark.
----- Original Message -----
From: "John Kortink" <kortink@...>
To: <bbc-micro@...>
Sent: Sunday, August 31, 2008 12:05 AM
Subject: Re: [BBC-Micro] FRAM....
>
> On Sat, 30 Aug 2008 21:31:11 +0200, John Kortink wrote:
>
>>[...]
>>
>>So you're asking for trouble if you don't validate
>>nCE with 2MHZE (or, therefore, nOE, which has 2MHZE
>>factored in). Without that, it may work some of the
>>time, but when the first glitch on nCE comes (and
>>there will be many) you're screwed.
>
> The proof of the pudding : validate nCE by adding an
> OR gate, inputs phi1 (e.g. IC29 pin 1) and S21 'se',
> output S21 'sw'. E.g. by piggy-backing a 74LS32 onto
> IC29 (connecting pins 1,7,14) and linking pin 2 and
> 3 of the new one to S21 'se' and 'sw' respectively.
>
> For argument's sake I just tried this and, hey presto,
> FRAM fully working as ordered, and looking stable.
>
> Do note that I tap IC77 pin 8 for my write strobe,
> although using the often (ab)used 6502 RnW should
> be okay too.
>
>
> John Kortink
>
> --
>
> Email : kortink@...
> Homepage : http://www.inter.nl.net/users/J.Kortink
>
> GoMMC, the ultimate BBC B/Master/Electron storage system :
> http://web.inter.nl.net/users/J.Kortink/home/hardware/gommc
>
>
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