On 17 Jul 98 at 20:45, [log in to unmask] wrote:

> I have access to a  couple of old PC mono adaptors.  They have
> 64KB of dram and a parallel port.  How can I tell if these are
> "hercules compatible" or knockoffs of the older IBM MDA?

  The 64KB is the giveaway.  The MDA only had 4KB of RAM for text
(25x80 = 2000 character-attribute pairs).  The earliest Hercules had
32KB for a graphics page, and later cards offered two pages (if no
CGA/EGA/VGA was present) for a total of 64KB.

> Secondly, a related question: Where can I find the horizontal and
> vertical scan frequencies for a PC monochrome (amber) monitor?  I
> need these, if I can get a Hercules clone, to install XFree86 on my
> linux system.

  I have an old IBM technical reference at home, which may contain
those numbers -- I'll look tonight.  They may also appear in Richard
Wilton's "Programmer's Guide to PC and PS/2 Video Systems" -- my copy
is not currently accessible.
  [The fact that the monitor is amber shouldn't be relevant, but the
fact that it uses TTL signals is.]

  I did a web search, and I believe I've found that the hroizontal
frequency is 18.43 KHz, with a vertical frequency of 50 Hz.  See

http://www.heartlab.rri.uwo.ca/vidfaq/part3.html#MDACGAEGAmonitors

David G