claudio@ethz.UUCP (Claudio Nieder) (06/02/86)
1. Extra Halfbrite mode
Last friday I got a copy of the Public Domain Disk #1. On this disk
I found the 'halfbrite' program which should show a 6-bitplane screen
with 64 different colors. I tried it, but my Amiga displays the same
32 colors twice instead of 64 different colors, seams I got the old
graphic chip. The same holds for red and kussi, their Amigas also
don't display 64 colors.
My question: is it possible to obtain the newer graphic chip, to replace
the old ones ?
2. External sync
This weekend I tried to externally synchronize the video display of my
Amiga. I built a circuit to extract the VSync and HSync out of the
video signal of my TV set. I fed the sync signals into the Amiga
and switched it on to see what happens. After loading the Kickstart
floppy the Amiga recognized automatically (!) that some external
sync signals are available and switched into external sync mode.
But now the troubles began:
My sync signals agree with the european television standard, 50 pictures
per second, 625 lines i.e. 15625 lines per second. The Amiga works with
60 pictures per second and 15750 lines per second. The results were
a) After about 1/60th second the Amiga includes an own VSync pulse in
the Composit Sync Output, it doesn't wait for the externally supplied one.
b) There is some quite remarkable jitter in the HSync pulses of the Composit
Sync Output signal.
I assume that both effects arise due to the different timing in the
Amiga (US TV standard) and in my sync signals. I looked into the hardware
manual for any indication how to change this timing, but I didn't find
how to change the total number of pixel per lines and lines per screen in
the Amiga. Is there any way to do it by software (most video controller
today allow this) or is it necessary to change the hardware ?
I hope somebody at C-A can help me. Please post the answer to the net,
it probably interests a lot of people in Europe.
Thanx
Claudio