BBC conversion card - what is this switch?

discussion of games, software, hardware & emulators relating to the Acorn Atom and Acorn System machines.
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wolfgang
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BBC conversion card - what is this switch?

Post by wolfgang » Fri Mar 23, 2018 8:08 pm

Hi,

I got an Atom with a BBC conversion card. It is in bad shape, very poor soldering. :(
Anyhow, there is a switch connected to the Atom PCB rigth under ICs 44 and 45.
The track between R26 and the hole that connects to pin 13 of IC44 is cut.
Switch
- position 1 reconnects the cut track
- position 2 connects pin 13 of IC44 to pin 10 IC9

What is the purpose?
Furthermore, can someone please point me to an installation manual for the card?
Thanks,
Wolfgang

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hoglet
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Re: BBC conversion card - what is this switch?

Post by hoglet » Fri Mar 23, 2018 8:36 pm

wolfgang wrote: Furthermore, can someone please point me to an installation manual for the card?
http://www.acornatom.nl/hardware/bbc/AtomBBC_fig5.zip
and more here:
http://www.acornatom.nl/hardware/bbc/atbbc.html

Dave

wolfgang
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Joined: Wed Jun 07, 2006 11:12 am
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Re: BBC conversion card - what is this switch?

Post by wolfgang » Sat Mar 24, 2018 12:09 am

Thanks Dave!
I totally spaced out and forgot to attach the picture that I took.
switchBBCcard-s.jpg
By looking at the diagram, I found out what the switch does. It switches between the original 4.00MHz signal and the 3.58MHz signal (for the 6847) and feeds the signal to the 6502.
Why? To synchronize the CPU with the VDU? :-k :-k

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