Re: a USB for the Apple II smoke test

[Roger Johnstone <rojaws@orcon.net.nz>]

In <pan.2005.07.29.16.51.53.149868@emeraldcity.gov> The Wizard of Oz  
wrote:

> Since there are serial mice for older Apples and the 
> software appears to exist in GSOS (backwards compatibility) then a USB 
> mouse *should* work if properly connected. All he would have to do 
> would be to match the data format and baud rate.

Apple never made any RS232-type serial mice. The original mice sold for 
the early Macs, Apple II mouse card and Apple IIc have no processing 
circuitry in them at all. They rely on simple optical switches turning 
on and off as the ball rotates, which the CPU in the computer counts to 
work out how far it's moved. Each signal (X1, X2, Y1, Y2, button) has 
its own connection in the mouse cable.

The serial mice used with IBM PCs have their own microcontroller inside 
them which detects the movement, then sends that as serial data to the 
computer. ADB mice use the same scheme, except they use a significantly 
different protocol since they have to share a bus with multiple devices. 
In fact USB is a lot closer to ADB than it is to RS232 serial.

-- 
Roger Johnstone, Invercargill, New Zealand
http://vintageware.orcon.net.nz/
________________________________________________________________________
  No Silicon Heaven? Preposterous! Where would all the calculators go?

              Kryten, from the Red Dwarf episode "The Last Day"