TV Out Question...

bmb!

I've read the book and searched the forums, so I hope this hasn't been asked hundred times before....

I understand the 3-bit DAC for the composite video out but do I need the 4th resistor for the "aural subcarrier". I'm just stumped by the note on the schematic... "This resistor is only required for aural subcarrier in broadcast mode" What is that? And do I want it? If possible I wouldn't mind leaving that pin free for other uses...

Thanks, in advance for the help...

Mike Huselton

Aural Subcarrier = Sound. Omit this pin if you don't want sound.

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JMH

Baggers

I thought it was for broadcasting?
as my first stuff was just the three pins, so if you're connecting direct to composite, then you don't need the fourth resistor and pin.
be aware though to remove that pin dir activity from any tv display driver you use, as that may cause you problems when you're not expecting it, trying to debug some unexpected data coming out of the port. [noparse]:)[/noparse]

Post Edited (Baggers) : 12/18/2007 4:06:26 PM GMT

kittmaster

I've designed in all four resistors into my new board, I just added a jumper to the four resistor for easy switching in or out if it is needed.

Rayman

I've heard that broadcast mode doesn't work so great. So, I would just leave it off... On the other hand, Mike Green said it does work somewhat on Channel 3 (at least the video), so you might want it...

Paul_H

I wonder - can the 4th pin be used for other purposes if we/re not using it for broadcast mode?

Paul

deSilva

Don't wonder any longer.. Yes, it can. If it is not configured in the TV driver setting it will not be used by the Video Logic.

Paul_H

Thanks desilva,

I'm reading through TV.SPIN now to see what I need to to to recover my pin 15

Paul

deSilva

Just avoid the settings with "chroma" and "aural"
It is also little known, that the Video Logic outputs on EIGHT pins by default! However 4 (or 5) of them are generally suppressed by your settings.

''  tv_pins
''
''    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
''
''    bits 3..0 select pin group mode:
''      %0000: %0000_0111    -                    baseband
''      %0001: %0000_0111    -                    broadcast
''      %0010: %0000_1111    -                    baseband + chroma
''      %0011: %0000_1111    -                    broadcast + aural
''      %0100: %0111_0000    broadcast            -
''      %0101: %0111_0000    baseband             -
''      %0110: %1111_0000    broadcast + aural    -
''      %0111: %1111_0000    baseband + chroma    -
''      %1000: %0111_0111    broadcast            baseband
''      %1001: %0111_0111    baseband             broadcast
''      %1010: %0111_1111    broadcast            baseband + chroma
''      %1011: %0111_1111    baseband             broadcast + aural
''      %1100: %1111_0111    broadcast + aural    baseband
''      %1101: %1111_0111    baseband + chroma    broadcast
''      %1110: %1111_1111    broadcast + aural    baseband + chroma
''      %1111: %1111_1111    baseband + chroma    broadcast + aural
''      -----------------------------------------------------------
''            active pins    top nibble           bottom nibble
''
''      the baseband signal nibble is arranged as:
''        bit 3: chroma signal for s-video (attach via 560-ohm resistor)
''        bits 2..0: baseband video (sum 270/560/1100-ohm resistors to form 75-ohm 1V signal)
''
''      the broadcast signal nibble is arranged as:
''        bit 3: aural subcarrier (sum 560-ohm resistor into network below)
''        bits 2..0: visual carrier (sum 270/560/1100-ohm resistors to form 75-ohm 1V signal)

Mike Huselton

I stand corrected.

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JMH