Question re video mode pins
Dr_Acula
Posts: 5,484
In a number of the TV drivers there is this code:
Would someone be able to kindly explain this a bit more. I'm using "%010" at the moment which is pins 23-16, but in practice this is actually pins 16,17 and 18. Is it possible to make this, say, pins 21,22,23?
The reason I ask is that I'm experimenting with fast external memory, and this means more pins need to be devoted to driving the external memory chip. This has led me down a path that seeks to recycle pins 28,29 (the eeprom) and pins 30,31 (the serial download pins). I have a circuit that uses a 4066 chip to isolate these lines from the eeprom and the serial download chip once 3 seconds have elapsed after a reset (the timer is also reset by the serial Tx line, for very long C program downloads).
I figured that maybe 3 of those lines could be for TV, and a fourth for audio, as these would be things that one might want more commonly than other things.
If it is too hard though to rejig the mode in the TV code to use these pins, maybe I could put the keyboard and mouse on pins 28-31, and the TV plus audio on pins 24-27.
Thoughts would be most appreciated.
'' bits 6..4 select pin group: '' %000: pins 7..0 '' %001: pins 15..8 '' %010: pins 23..16 '' %011: pins 31..24 '' %100: pins 39..32 '' %101: pins 47..40 '' %110: pins 55..48 '' %111: pins 63..56
Would someone be able to kindly explain this a bit more. I'm using "%010" at the moment which is pins 23-16, but in practice this is actually pins 16,17 and 18. Is it possible to make this, say, pins 21,22,23?
The reason I ask is that I'm experimenting with fast external memory, and this means more pins need to be devoted to driving the external memory chip. This has led me down a path that seeks to recycle pins 28,29 (the eeprom) and pins 30,31 (the serial download pins). I have a circuit that uses a 4066 chip to isolate these lines from the eeprom and the serial download chip once 3 seconds have elapsed after a reset (the timer is also reset by the serial Tx line, for very long C program downloads).
I figured that maybe 3 of those lines could be for TV, and a fourth for audio, as these would be things that one might want more commonly than other things.
If it is too hard though to rejig the mode in the TV code to use these pins, maybe I could put the keyboard and mouse on pins 28-31, and the TV plus audio on pins 24-27.
Thoughts would be most appreciated.
Comments
The 0000 was found by trial and error. I note that the demo board is 0101 and that is pins 12,13,14. I can't quite see the formula that relates the prop pins to the modepins.
If it is possible to change " modepins" so it works on, say, pins 28,29,30, that would be great!
This would be pingroup 3 and the high nibble which for you should be %011_0100.
Another quick question - how do you put "solved" next to a thread?