Re: Videx graphic switch ????

[Wayne Stewart <waynes@telus.spamless.net>]

akessel wrote:
> I acquired a little board about 1 inch by 2 inchs that attaches to videx
> videoterm boards video out, and probably the apple II video in for
> switching.  This is not a hard switch though.  it appears to attach to the
> apple II game port (guessing) - has connectors to go into the usual 16 pin
> dip.
>
> Anyone know about this board? how does it connect and how would it toggle
> between the different videos?
>
> Thanks, Andy


The videx Soft Video Switch. It basically allows the card to output either
40 or 80 column. The card goes in the socket of the chip at F-14. The chip
will either be a 9334 or a 74LS259. It's the chip on the far right on the
same row as the ROMs. The 5 pin connector should be facing the keyboard
and  the 4 pin the back of the computer.

How does it work? From the manual

"Soft Video Switch Theory of Operation.

The Soft Video Switch is controlled by two conditions: the state of 
annunciator zero and the color killer signal. If the color killer is 
off, the Apple ][ is in its color graphics mode and the Soft Video 
Switch will always display 40 columns (i.e. graphics). If the color 
killer is on, the Soft Video Switch follows the state of annunciator 
zero (set to off by Autostart on power up and reset). If the annunciator 
is off, the Soft Video Switch displays 40 columns. If the annunciator is 
 on, 80 columns is displayed. The firmware on the Videoterm sets 
annunciator zero on as EACH character is output. To turn annunciator 
zero on,  a memory reference to $C058 (�16296) must be made. To turn it 
off, $C059 (�16295)."

Email me if you want a PDF of the manual and can accept a 1.3mb
attachment(deleting the .spamless in my email address)

Wayne