IBM AT Drive Types

[Tony Duell]

> 
> The scanning frequencies of the EGA and MDA cards should be real close 
> (MDA outputs 348 lines of res, the EGA 350). You shouldn't have a 
> problem there (I won't comment about the jumpering/shorting though), but 
> keep in mind the original IBM mono monitor was very very touchy. If you 
> plugged it into a CGA card, it was known to...ummm...explode...

That's going a bit far. It's very easy to burn out the horizontal output 
transistor and maybe associated components, but it won't explode.

There is no horizontal osciallator in the MDA (5151) monitor. The Hsync 
line goes to the base of the horizontal driver transistor, the collector 
of which is transformer-coupled to the base of the horizontal output 
transistor. You can therefore attempt to drive the horizontal system at 
just about any frequency, but if the horizontal output stage is driven 
way off resonance (e.g. using the CGA frequncies), it will do nasty things.

>
>  I won't swear to it, but I had thought there was a way of configuring 
> it specifically for a mono monitor. Don't hold me to it though. 

There is. There are switch settings for the EGA card to drive the MDA 
monitor, CGA monitor, or EGA monitor (the latter can operate at 2 
different horizontal frequencies). The reason I mentioned the jumper link 
is that a lot of people forget to set that correctly when linking to a 
CGA or MDA monitor. 

-tony