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Lightpen

Submitted by Dan Dooré on Thu, 2006-04-20 10:09. Peripheral

N/A


Information from Andy Gale taken from the Sam Coupé Scrapbook

Very simple really - the SPEN pin on the lightpen/audio port is usually pulled high internally with a resistor. This means that ports 248 and 504 are constantly updated with the x and y coordinates respectively of the raster beam. If SPEN is held low then those ports ‘stick’ at their current value. So, basically, your lightpen circuit should hold SPEN low and blip it high very briefly when the raster beam passes in front of the photodetector (you could use a photodiode, phototransistor, photodarlington - preferrably a fast one) - this shouldn’t take much more than one i.c.! Note that the x-resolution is not too great, and that line interrupts (often used for palette changes) will not operate. Sorry.


No pen actually ever got released for the Sam.

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light gun spliter

Submitted by rogerjowett on Wed, 2010-10-13 18:12.

any chance of splitting the light gun inputs so that two can be read?

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Re: light gun splitter

Submitted by ascii on Thu, 2010-10-14 13:08.

No - there’s only one counter in the ASIC, so two light guns would have to be implemented with a completely different scheme to the one the Sam internally uses.

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