On Sun, 24 Oct 1999, Larry Anderson wrote:
> **also in related news I picked up a 'petunia' board for the PET and an
> article on computer music by hal chamberlin, The petunia board has a working
> composite video circuit for the PET (will have to check it against Nick
> Hampshire's and MICRO's to see which one is employed, if those.) and the
> Chamberlin article essentially shows how to make the four-voice music circuit
> used in the MTU and the Petunia music boards.
I've found the settings to use the Petunia video board on a PET with a
CRTC.
REGISTER VALUE
0 63
1 40
2 49
3 15
4 31
5 7
6 25
7 29
This sets the CRTC to a NTSC compatible mode. You must change character
sets by poking the interface chip as in the older PETs. Printing the
character to change character sets will reset the CRTC.
You must also add a 1600 picofarad capacitor in parallel to C1.
I also find that adding a 0.01 mfd capacitor across pins 9 and 10 of the
user port connectore helps to suppress video noise.
-
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