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Still
looking for the x-y encoder?
Think at what you're clicking on - it's your mouse.
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The mysterious X-sensors Ltd. doesn't exist. If you
already discovered it, congratulations! Not many designers think at the mouse as an incremental x-y encoder, and many more don't even know how to use it. As discovering the mouse secrets is as simple as monitoring a serial connection, the worst kept information technology secret remains unknown to most of us! |
How Microsoft (tm) mouse works
The mouse connects to any RS232 serial port (COM1, 2, etc.). In its basic form, it uses only RX (PC side) and GND to communicate, while the RTS (sometimes coupled with TX) line is used as a power source to feed mouse circuitry. Every time you move the mouse, or just press or release a button, three bytes are sent over the serial line at a speed of 1200 baud, 8 data bits, no parity, two stop bits.
| MSB= B7 | B6 | B5 | B4 | B3 | B2 | B1 | LSB=B0 | |
| first byte | 1 | 1 | L | R | Y7 | Y6 | X7 | X6 |
| second byte | 1 | 0 | X5 | X4 | X3 | X2 | X1 | X0 |
| third byte | 1 | 0 | Y5 | Y4 | Y3 | Y2 | Y1 | Y0 |
L and R are the status of the left
and right buttons, 0 = released and 1 = pressed.
X7..X0 and Y7..Y0 are the binary digits of the X and Y counters. They hold
the number of X and Y steps from last transmission. This makes the mouse a
relative encoder, that is there is no "zero" or absolute position
as every movement is relative to the last position transmitted.
I'm waiting for your suggestions: what would you do with it? Not many years ago, engineers would have killed for an hardware like this! E-mail me your ideas!
I built this provokation to let you think about a few points:
1) Our everyday's life involves much more high technology than we are aware of.
2) Mass production can make high technology simple, cheap, widespread and available.
3) In the beginning, it doesn't matter if a technology is expensive or difficult to design. If it is useful, people will use it. The Moore's law and mass production will make it affordable in the long run. First mouses were research lab tools for edge CAD technologist.
Some other everyday's life examples are: cars, remote control, cellular phones, color printers, CD players. And now internet capable devices are coming...
Last update 22/11/98.
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