Re: (no subject given)

[david@uow.edu.au (David Wilson)]

mab22@po.CWRU.Edu (Michael A. Balfour) writes:
>This might sound like a silly question, but I really don't understand:
>how does Flashing text work in the Apple II series of computers.  I've
>been looking through Apple IIe schematics, and I don't see any video
>invert signals tied to the output of the character generator ROM.

>My assumption is that the IOU chip is switching between normal and
>inverse text at some unknown constant rate.  Can anybody confirm/refute
>this assumption?  Any idea what that rate is?  Does anybody have Apple
>II+ schematics where the IOU logic was all contained in TTL logic?

Correct (this also explains why the mousetext characters were put where they
were - if they were put in the obvious position ($00-$1F) they would have
broken flashing characters.

A full description can be found in Jim Sather's Understanding the Apple //e.

The ][+ schematics can be found in Jim Sather's Understanding the Apple ][.

The ][(+) uses a 555 timer chip to invert the flashing characters.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia  david@uow.edu.au