10 Jun
2004
10 Jun
'04
3:13 p.m.
On Fri, Jun 11, 2004 at 12:05:55AM +0100, Tony Duell wrote:
Commodore was one of the last home computer companies to make schematics
available. The A500/A2000 tech reference has the schematics, and even
15 years ago, ordinary people could buy it (i.e., it wasn't restricted
to service centers only).
None of this
connects up in a way which gives me colour on the display.
_NOW_ do you know why I like to have schemaitcs to everything :-). In any case, assuming the RGB signals are compatible
(I assume the Amiaga
outpus analogue RGB at TV rates), you'd get a better picture using them.
It should just be a matter of matching up the signals on the 2 connectors.
Yes... the Amiga just slammed out colors on the R, G and B pins at either
PAL or NTSC frequencies (~15KHz, not 31KHz like VGA), at least for older
models and those without "flicker fixers" (buffering hardware that would
accept 15KHz input and emit 31KHz output to use with a VGA-style monitor,
integral to the A3000, and a card option for other models).
What I can't remember without looking it up is how Amigas handled sync
pulses... it's nothing bizarre, but I forget if it's HSync/VSync positive
or negative logic. Since I typically used C= monitors, it was only ever
an issue once - I got an upgrade board for a C= 1702 (C-64 chroma/luma/
composite) monitor that added RGBI for the C-128. I hacked the board a
bit and got it to work with analog RGB on my A1000 before I could afford
a "proper" RGB monitor. One part of the hack was an external sync pulse
inverter. I etched my own PCB and put a DPDT switch and a 7404 on the
sync signals so I could invert or buffer the sync pulses.
It worked great until my house was broken into in 1990 and they stole it,
my A500 (a game machine next to my workhorse A1000) and a couple of PETs.
The A1000 was lying face down next to everything - they almost got it, too.
The real loss, though, was my "WEDGE" for the A500 - a rare device that
plugged into the expansion socket and provided an 8bit ISA slot. I had
modified mine to work with serial boards as well as MFM HDCs (additional
IRQ wiring). A500s were cheap even then... I've never seen another WEDGE,
ever.
-ethan
--
Ethan Dicks, A-130-S Current South Pole Weather at 11-Jun-2004 03:00 Z
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