Preventing CGA revisionist history

Tony Duell ard at
Wed Jan 18 11:08:27 CST 2006

> On 1/18/2006 at 12:13 PM mbbrutman-cctalk at wrote:
> >If you look at IBM documentation (especially the BASIC manuals from the
> >era) it is clearly listed as Brown, not dark yellow.
> Looks like the network around Q204/Q205 is the dark-yellow to brown
> translation in the IBM CGA montor.  I can scan that part of the circuit and
> post it if anyone's interested.

I wonder if we're looking at different schematics. In mine, Q204 and Q205 
form the buffer stage for the Hsync signal. The emitter of Q205 seems to 
be a blanking signal. the collector feeds sync to Q402 (the deflection 
oscillator IC). 

In mine, Q206 is the 'brwon kludge' I think.

> I haven't checked, but wasn't there also special-casing in the EGA BIOS
> code to handle the dark yellow=brown case?

I doubt it. I seem to rememebr a PROM in the input stages of the 5154 
monitor, which may well have done the same conversion, though. 


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