teg@orc.olivetti.com (Tom Griner) (11/08/88)
There seems to be some misunderstanding about the functionality
of EGA cards (based on other messages I have seen here).
I hope this information is helpful to some:
If you buy an enhanced EGA card (That provides resolution higher
than 640x350) the extended modes will only work on a multisync
type monitor. Currently EGA monitors only come with two possible
scanning frequencies (1 Provides 640x200 CGA mode, and the other
gives 630x350 EGA mode). Many people have stated the intention
of buying a regular EGA monitor with an enhanced EGA card.
This combo gives only 640x350 maximum resolution. Someday
there may be non-autosync EGA monitors that could have a 3rd
frequency for 640x480 (or whatever), but I have not yet heard
of one (The complexity of providing so many discrete scanning
rates equals that of a full multi-syncronous monitor...).
The EGA cards with 800x600 mode refresh the screen (usually) at
56Hz instead of 60Hz. This is because most multi-sync monitors
max out at 35KHz bandwidth (which 800x600 at 60Hz would exceed).
This causes some flicker on monitors with fast phosphor, and
produces more eye strain when viewed for extended periods.
There were some messages about someones desire to hook a
composite monitor to an EGA card; Many CGA cards have composite
output (because CGA Horizontal Scan Frequency nearly matches
NTSC this is possible) that can be used with a composite color
monitor. Some extra-cheapo CGA cards provide an "adapter" that
you plug into the 9 pin connector. This adapter has an RCA type
connector that is said to be composite, but in fact it only
gives gray scale to a composite color monitor (the adapter just
contains different sized resistors connected between the RGB
pins and the composite connector).
Although most EGA cards have 2 RCA jacks on them, they do not
provide composite video output. The jacks are just wired to the
feature connector (the long connector on top of the EGA card) and
were meant for future expansion. I have seen an aftermarket
video overlay board that plugs into the feature connector, and
provided some functionality through the RCA jacks, but it cost
more than the EGA card itself.
I think that the ATI EGA Wizard card does allow you to have
a composite signal, but this card has many drawbacks that may
outweigh this advantage.
Tom Griner {decwrl, ucbvax, ...}!orc.olivetti.com!teg frames 2 /dev/fb
TEG@Bionet-20.bio.net presto.ig.com!teg flames 2 /dev/null
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