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Jumper W1 on XL Board

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I have a question to which I have not yet found an answer:

 

On the XL boards (and I think also on the XE boards) a bridge "W1" is drawn in the circuit diagram.
This connects on the Pokey pin 10 (P4) with pin 11 (P5).

 

On my board this bridge is set with a 0 ohm resistor.

 

I do not understand what function this bridge has and in what cases is it opened?

Can someone help me there?

 

W1.jpg

W1b.jpg

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Fairly sure P4 through P7 are wired together - they're the unused POT inputs that would otherwise go to controller ports 3 and 4 which XL/XE don't have.

I would think this is done to force a constant paddle value on those pins, if they were not connected to anything possibly they'd get some random floating value?

 

ed - most software will read the shadow registers - the XL OS mirrors the included port's controller values to the "missing" ones so that games that use those controllers can still have a chance of working.

 

On the 1200XL, one of the POTS has a settable jumper (POT 7 ? ) - likely used at the factory, it can force the computer to go to Self Test when powered on.

Edited by Rybags
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