13-10-2016, 01:40 PM
(12-10-2016, 07:40 PM)`FRANK.C Wrote: The circle will be produced by loading values into TIMER0 and TIMER1 from a table at the beginning of each line. One timer will be for the left edge of the circle the other for the right edge. When the timers overflows an interrupt will be called which will toggle which card can be seen on port C.
If my understanding of the Philips generator is right, they only use one timer which an up/down counter, zero being the centre point of the screen. I assume they use a comparator to generate the switching points.
There is also a facility, although I'm not sure if it is standard, to turn off the circle so that the central part is square, similar to your picture.
