MFJ-1278B MULTI-MODE COMPUTER INTERFACING
If your computer is configured as DCE, you will have to wire pin 2 of your MFJ-1278B to
pin 3 of the computer RS-232C connector. Then wire pin 2 of the computer's RS-232C
connector to pin 3 of your MFJ-1278B. Please note that pin 7 of the computer's RS-232C
connector will still connect to pin 7 of your MFJ-1278B serial port. Some computers may
require that pin 5 of the computer serial port connector be connected. Others may require
connections for pin 8 and pin 20. You can use the computer's output signals on pins 4 and 6
as shown in Fig. 2-3.
MFJ-1278B RS-232C Computer RS-232C
2 2
3 3
7 7
| 4
| 5
| 6
| 8
| 20
Fig. 2-3. Serial port wiring with jumpers for
auxiliary signals.
Other Computers with Nonstandard Serial Ports
Computers with non-standard serial ports must meet the following conditions.First, the signal
levels should be RS-232C compatible. The MFJ-1278B requires that the voltage levels sent
from the computer be greater than about +3 volts in one state and less than about +1 volt in
the other state.
Second, the polarity of the signals must conform to the RS- 232C standard. This means that
the low voltage state must correspond to a logical "1" and the high voltage state to a logical
"0".
Third, the computer must be able to correctly receive a signal that meets the RS-232C
specification. The MFJ-1278B supplies signals that meet this specification.
Make or buy a cable that provides the following connections. The common pin on the
computer's RS-232C serial port must be connected to pin 7 on the MFJ-1278B serial port.
Connect the line that sends data from the computer to pin 2 on the MFJ-1278B RS-232C
port. Connect the line that your computer receives data on to pin 3 on the MFJ-1278B RS-
232C port.
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