12-10-2016, 07:40 PM
Some weeks ago I seen a picture of a black and white telly displaying the PM5544 test card. It was only then that it struck me how clever the Phillips engineers were in designing this card and how memory efficient it was.
I just couldn't resist having a go at building a 405 card in this style.
I have decided to use a 18F14K22 PIC, it will have a clock speed of 60MHz giving a instruction rate of 15MHz. Pixel rate will be the same as the instruction rate.
I wanted a fast instruction rate as I will be using an interrupt and the faster the instruction rate the less disruption it will cause to the picture and 15MHz is a figure that will make producing the 1,1.5,2,2.5 and 3 MHz gratings easier.
The active line will be 80.266 uS long or 1204 pixels.
Front porch will be 1.67uS
Sync 9 uS
Back porch 7.866 uS
The card will actually be two cards which will be simultaneously available on port C of the microcontroller. The upper four bits will makeup one card, that will be the white and grey grid pattern background. The lower four bits will be a separate card, that will makeup the circle. At any time only one of the cards will be visible, this will be achieved by setting the pins of the unwanted card to inputs.
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.
Well that's the theory, we'll see what will jump out of the darkness to throw a spanner in the works.
The photos are of the white and grey grid pattern, this the completed pattern that is available on the upper four bits of port C.
The second photo is testing the interrupts. The timers were loaded with arbitrary values just to test them,. The dark area in the middle of the lines is when the lower four bits are switch in, there is no information on them yet hence they are black. The white horizontal lines are left in place for now as a reference.
The interrupts are pared back to the minimum and just take 7 cycles each to complete.
The last photo is of the circuit I am using.
Frank
I just couldn't resist having a go at building a 405 card in this style.
I have decided to use a 18F14K22 PIC, it will have a clock speed of 60MHz giving a instruction rate of 15MHz. Pixel rate will be the same as the instruction rate.
I wanted a fast instruction rate as I will be using an interrupt and the faster the instruction rate the less disruption it will cause to the picture and 15MHz is a figure that will make producing the 1,1.5,2,2.5 and 3 MHz gratings easier.
The active line will be 80.266 uS long or 1204 pixels.
Front porch will be 1.67uS
Sync 9 uS
Back porch 7.866 uS
The card will actually be two cards which will be simultaneously available on port C of the microcontroller. The upper four bits will makeup one card, that will be the white and grey grid pattern background. The lower four bits will be a separate card, that will makeup the circle. At any time only one of the cards will be visible, this will be achieved by setting the pins of the unwanted card to inputs.
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.
Well that's the theory, we'll see what will jump out of the darkness to throw a spanner in the works.
The photos are of the white and grey grid pattern, this the completed pattern that is available on the upper four bits of port C.
The second photo is testing the interrupts. The timers were loaded with arbitrary values just to test them,. The dark area in the middle of the lines is when the lower four bits are switch in, there is no information on them yet hence they are black. The white horizontal lines are left in place for now as a reference.
The interrupts are pared back to the minimum and just take 7 cycles each to complete.
The last photo is of the circuit I am using.
Frank