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Vanguard Multiport 4520CP Controller User’s Guide A-5
Asynchronous Serial Cables
FIGURE 7. Asynchronous Modem Cable (DTE to DCE)
Asynchronous Null-Modem Cables
Null-modem cables are designed to connect devices that send and receive data on
the same pins, which is the case when you connect a DTE device to another DTE
device. Because both devices are trying to send and receive on the same pin, the
wiring of the cable must swap those signals.
Since the Vanguard Multiport cards are configured as DTE devices, you must use a
null-modem cable to connect them to other DTE devices such as terminals, printers,
and plotters.
There are several different types of null-modem cables available. Three of the most
common ones are
• XON/XOFF
• Request-To-Send (RTS)
• Data Terminal Ready (DTR)
The difference among the three cable types is the flow control they support:
• XON/XOFF supports software flow control only, with its three-wire configura-
tion for XON/XOFF handshaking (see Figure 8).
• RTS supports hardware handshaking when the peripheral uses the Request To
Send (pin 4) signal (see Figure 9).
• DTR supports hardware handshaking when the peripheral uses the Data Termi-
nal Ready (pin 20) signal (see Figure 10).
2
3
4
5
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7
8
20
2
3
4
5
6
7
8
20
Vanguard Multi-
port Connector
Modem
Connector
Modem
Cable
DTE DCE