On 06/21/2017 07:29 PM, firstname.lastname@example.org wrote: > >> On 2017-06-21, at 19:17, Gerrit Heitsch <email@example.com> wrote: >> >>>> Excellent fun! It sees if the light pen interrupt can be triggered >>>> between raster lines x'136 and 2; if so, it's a 6569R1, if not, not. >>> That's very interesting too! How does one trigger LP IRQ from within software alone? Is it a kind of raster position / CIA port combination? >> >> Well, the LP Input is connected to the joystick ports and shares a Pin with PB4 of the CIA on U1. > > Hardware side sure. What I meant was... > >> So you can trigger LP IRQs via software. > > ... that I never used LP IRQs but thought that it would trigger only when the button line is grounded within a specific timing window so some kind of synchronisation with raster position would be required for the IRQ to happen. But that's a different subject anyway. No, the LP IRQ just latches the current X and Y position of the electron beam when you get the high to low transition on the LP line. And you also get an IRQ to notify you of that event. The idea was to have a light pen, meaning a photo cell held against the screen (needs a CRT, won't work on a TFT) and detect when the beam comes by. With the right software you could draw on the screen with it. So you can just trigger an LP event including IRQ by software via PB4 and then check the registers. Doing this at different times (use $D012 to determine when) will help you differentiate between a 659R1 and the other PAL-VICs. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2017-06-21 18:04:07
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