2-17
2
2.7.3.2 Serial Header Connections
The Serial Header J4 is a 10-pin male header with 0.025 square pins on 0.1
centers. Pin 8 is the key position and is omitted from the header. The Serial
Header location on the 4863 lower board is shown in Figure 2-6. Signal pin
assignments are listed in Table 2-2.
TABLE 2-2 SERIAL HEADER PIN ASSIGNMENTS
Pin
Signal
Function
1
Chassis
Shield tie point
2
RxD
RS-232 Input
3
TxD
RS-232 Output
4
Tx/Rx+
RS-485 + Signal
5
Tx/Rx-
RS-485 - Signal
6
Vcc
+ 5 Vdc
7
Ground
RS-232 Signal Ground
8
-
key
9
Ground
Logic Ground
10
Reset#
Reset Input. A low input resets the 4863.
Table 2-3 shows a suggested way to wire the serial connections to a 25-pin
or a 9-pin connector. The RS-232 Standard specifies female connectors
(DB-25S) for DCE devices and male connectors (DB-25P) for DTE
devices. Because the 4863 only has Tx and Rx signals, the user can easily
make a Data Terminal (DTE) or Data Communication (DCE) style interface
for the end product by adding the appropriate jumpers and voltages as
shown in Table 2-3. The recommendation is to add the jumpers in case the
mating device uses hardware handshaking signals.
RS-485 interfaces do not have a standard interface connector. Our
recommendation is to use a 9 pin or smaller connector. The 4863's RS-485
interface operates in the half-duplex mode and has a resistor network that
biases the RS-485 signals to the mark (logic '1') condition when they are not
being driven. The resistor network has 1 kohm pullup and pulldown
resistors on each side of a 220 ohm load resistor. This resistor network
should be sufficient for cables distances up to 100 feet in length. For longer
length cables, the user should provide a similar network at the other end of
the serial link.
