Peritek VCD-V, User Manual

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Peritek
Installing Your Peritek Graphics Board 2-25
The mouse relies on the current which can be sourced through the serial
port's transmit, RTS and CTS lines for power. However, since the graphics
board mouse port is really just data leads only, fused +12 and -12 volts are
supplied to these lines instead.
Both Peritek Mouse units are suitable for applications which require long
cables, because they use the RS-232C electrical protocol which can
support cable lengths well in excess of 100 feet. Peritek uses a DB9 male
D-Sub connector to pass data and power to the mouse, which re12
and -12.
Note
If you experience difficulty getting a device to work, especially a Mouse or
Trackball, you may be drawing too much current from pins 3, 4, or 7.
There are current limiting resistors in series with the power sources for
these lines.
Table 2-12 Mouse Connector Pinout
9-pin D-Sub Pin Number Description
1 not used
2 Data from Mouse
3 -12 Volts via 470 ohm resistor
4 +12 Volts via 1000 ohm resistor
5 Ground
6 not used
7 +12 Volts via 1000 ohm resistor
8 not used
9 not used
The resistors are to make the marginal RS-232 circuits of low-cost mice
and trackballs work correctly. They also limit current inrush which can
damage some devices.