To: bdu95398@strath.ac.uk
Subject: Re: laceScan                                                                    


On Mon, 9 Jun 1997 01:41:06  David Beaton <bdu95398@st wrote: 
>
>I'm in the proccess of altering my  TOS 1.4 520ST FM (with 4Mb 
>Marpet) to fit the lacescan circuit board.

I'm glad to hear it David.


>I have two problems:
>
>The first problem is that I don't know which ACIA chip is the
>keyboard one.

On my STFM circuit diagrams, as well as on the boards I have, the
6850 ACIA chips are marked U52 (for Midi) and U54 (for keyboard).
You can verify by resistance measurement between Pin 2 (RxD) of
the keyboard ACIA to pin 5 of the 8 pin SIL keyboard connector.
This should be very close to zero ohms (a short that is).


>The second problem is that on my computer the 5th pins on the
>two ACIA chips are not connected as the instuction say they are.

This does vary with various revisions.  I believe this 'short'
is far more common on Mega STs.  Both these pins are unused
outputs, and should not be connected anywhere, and least of
all to each other.  That is a design error in those revisions
which have this 'short'.


>Could the instructions mean pins 20 as these are joined together
>on my computer?

Absolutely *not*. Pins 15-22 connect CPU data bus bits 8-15 to
both of the ACIAs, so touching any of these is wrong.

It is definitely pin 5 of the keyboard ACIA which is the unused
RTS output.  This is the pin that should control LaceScan mode.


>Thank you in advance for any advice,

You're welcome.

-------------------------------------------------------------------------
Regards:  Ronald Andersson                     mailto:dlanor@oden.se
                                               http://www.oden.se/~dlanor
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