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Serial Port Functions
The serial port provides a variety of functions. Modem connection to the serial port
allows access to the internet. Synchronous X.25 modems are used for
telecommunications in Europe. An ASCII text window is accessible through the serial
port on non-graphic systems. Low-speed printers, button boxes (for CAD/CAM
applications) and exotic devices that function like a mouse are also accessible
through the serial port. The additional speed of the serial port can be used to execute
communications with a CSU/DSU for a partial T1 line to the internet at 384 Kbaud
per second.
EIA Levels
Each serial port supports both RS-232 and RS-423 protocols. RS-232 signaling levels
are between -3 VDC and -15 VDC and +3 VDC and +15 VDC. A binary 1 (0012) is
anything greater than +3 VDC and a binary 0 (0002) is anything less than -3 VDC.
The signal is undefined in the transition area between -3 VDC and +3 VDC. The line
driver switches at -10 VDC and +10 VDC with a maximum of -12 VDC and +12 VDC
in RS-232 mode. RS-423 is similar except that signaling levels are between -4 VDC to
-6 VDC and +4 VDC and +6 VDC. The line driver switches at -5.3 VDC and +5.3
VDC with a maximum of -6 V and +6 VDC. Switching from RS-232 to RS-423
protocol is accomplished by changing jumpers J2604 and J2605. Jumper positions 1
and 2 are for RS-232 and jumper positions 2 and 3 are for RS-423.
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Sun Enterprise 220R Server Service Manual ♦ January 2000, Revision A