gunpilot8161@gmail.com
2013-09-10 19:37:06 UTC
Das
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Sent from my Verizon Wireless 4GLTE smartphone
----- Reply message -----
From: "John Coffman" <johninsd-***@public.gmane.org>
To: <n8vem-/***@public.gmane.org>
Subject: [N8VEM: 16137] Color VDU - no video output...
Date: Tue, Sep 10, 2013 7:51 am
On 09/10/2013 06:58 AM, Bryan Thompson wrote:
I note in the posted BOM that there are multiple
frequencies for oscillator P24 - 16.000MHz and 16.257MHz. I
currently have a 16.000 MHz one installed. Do we know if
they're both acceptable, or if I need one or the other
specifically for an EGA output?
Dan used a 16.000Mhz oscillator on his prototype board, but he used
the 10-pin CGA connector to connect to a CGA->VGA converter
board. The timing parameters he used are different.
EGA uses 16.257Mhz for the dot clock; 9-bit character width; 97 or
98 characters per line, of which 80 are active; 368 horizontal lines
at a frequency of near 15750Hz, of which 350 are active; the
vertical refresh is in the range 47-50Hz. The EGA alpha screen is
thus 720x350 dots.
16.000Mhz would require tweaking the timing parameters a bit; but a
monitor should show at least some output. Since your last post, I
tried an old "multisync" VGA monitor in place of the LCD. This
monitor was used with the uPD7220 graphics board and is known to
sync on 640x480 VGA and 800x600 XGA. The oscillators used are 25Mhz
and 40Mhz, respectively. However, the monitor does not sync on the
ColorVDU; but there is enough snow on the screen to make out text
and colors -- not enough to be readable or usable. I tried all 4
sync combinations with the same result. The point is, an unsuitable
monitor will show that there is ColorVDU output at the VGA
connector.
--John
[By comparison, true CGA timing uses a 14.318Mhz oscillator and
different timing parameter setup for the 8563. I have not tried CGA
since I have no such monitor.]
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Sent from my Verizon Wireless 4GLTE smartphone
----- Reply message -----
From: "John Coffman" <johninsd-***@public.gmane.org>
To: <n8vem-/***@public.gmane.org>
Subject: [N8VEM: 16137] Color VDU - no video output...
Date: Tue, Sep 10, 2013 7:51 am
On 09/10/2013 06:58 AM, Bryan Thompson wrote:
I note in the posted BOM that there are multiple
frequencies for oscillator P24 - 16.000MHz and 16.257MHz. I
currently have a 16.000 MHz one installed. Do we know if
they're both acceptable, or if I need one or the other
specifically for an EGA output?
Dan used a 16.000Mhz oscillator on his prototype board, but he used
the 10-pin CGA connector to connect to a CGA->VGA converter
board. The timing parameters he used are different.
EGA uses 16.257Mhz for the dot clock; 9-bit character width; 97 or
98 characters per line, of which 80 are active; 368 horizontal lines
at a frequency of near 15750Hz, of which 350 are active; the
vertical refresh is in the range 47-50Hz. The EGA alpha screen is
thus 720x350 dots.
16.000Mhz would require tweaking the timing parameters a bit; but a
monitor should show at least some output. Since your last post, I
tried an old "multisync" VGA monitor in place of the LCD. This
monitor was used with the uPD7220 graphics board and is known to
sync on 640x480 VGA and 800x600 XGA. The oscillators used are 25Mhz
and 40Mhz, respectively. However, the monitor does not sync on the
ColorVDU; but there is enough snow on the screen to make out text
and colors -- not enough to be readable or usable. I tried all 4
sync combinations with the same result. The point is, an unsuitable
monitor will show that there is ColorVDU output at the VGA
connector.
--John
[By comparison, true CGA timing uses a 14.318Mhz oscillator and
different timing parameter setup for the 8563. I have not tried CGA
since I have no such monitor.]
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