James Fraser wrote: > Hello, > > --- On Mon, 6/8/09, Clark Martin <[email protected]> wrote: > > >> The Mac Plus and earlier mice use discrete signals (wires) >> carrying the mouse click and encoding phases (two each) of the mouse X >> & Y directions (as well as power and ground). ADB (Apple Desktop >> Bus) transmits data bi-directionally on it's bus. It can do this for a >> number of devices connected to the same bus. It is much like USB >> although slower and limited in available devices. >> > > Let me see if I understand this correctly: > > The primary difference between a Mac Plus mouse and an ADB mouse > is that, in the former, there is very little circuit decoding done inside of > the mouse: the decoding is done by the Mac itself. > > But the ADB mouse is able to perform most of the decoding work inside itself > and send data signals direct to the CPU indicating what is happening to the > mouse at any given time. > > Does that sound right?
The Mac Plus/etc mouse is a pretty dumb device generally speaking - the sensors are wired straight into a 6522 which generated an interrupt whenever the mouse moved a notch any direction and a line to sense the button. Pretty simple design, but not very flexible. It worked for the one design of mouse, and not much else. Functionally speaking, ADB is somewhat similar to USB from a logical perspective (Greatly simplifying - this is not to say there's any chance of adapting between the two without significant work, just that when thinking about them they're similarly set up). Each device is assigned an address, which is used by the hardware and OS to address it specifically and tell it apart on the line and read registers from it. It could, theoretically, have been used for a lot more than it was - networking, storage, etc. It just ended up not being practical with the other options available. Lots of good in-depth info on both here: http://folklore.org/StoryView.py?project=Macintosh&story=Apple_II_Mouse_Card.txt http://en.wikipedia.org/wiki/Apple_desktop_bus If you *really* want the nitty-gritty, then you can also read http://developer.apple.com/documentation/mac/Devices/Devices-205.html Scott --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
