cb meeks wrote:
> That's actually where I got the information from. That page only really
> show a crude picture. It explains it uses a VIA and a flip-flop. What I
> was hoping to find is the schematics and possibly the driver. I think it
> would be awesome to preserve and build a replica of what Burrell designed.
I just read this article. This job can't be very complicated, IMHO. The
6522 is easy to connect to the bus. The address space is selected by
The connection of the mouse should be the same as in the Mac
The 74LS74 (half of it) is a bit more complicated. Q or /Q must be
connected to a port pin of the 6522. We cannot know which one they used
in the past. So it's your decision, i.e. PA0. /PRE and /CLR are set to
high. D is connected to D0 from the Applebus. CLK should be connected to
The rising edge of PHI0 transfers the level of D to Q. Q can be read
The article mentions the problem of a slow 6502 (10 cycles per loop) and
their solution running a loop of 17 cycles ("if the loop time was
relatively prime to the display frequency ..."). The job is to find the
one and only '0' on the data bus while video scanner is on. They set the
whole screen to '1', and when vertical/horizonatal blanking is on the
pullups set the bus also to '1'.
Easy and very smart, IMHO.