
2-23
2
The 4899A/4809A's internal pullup resistor at pin 20 is used to pullup the
SD(B) and RD(B) lines and apply a positive signal to the Tx/Rx- line. A
1 kohm resistor from SD(A) and RD(A) to ground is the pulldown resistor
for the Tx/Rx+ line. The 220 ohm load resistor completes the circuit.
98
99
CC
CA
CB
B5
D6
D5
EZ
8
AC Power
4899A/4809A
DB-25P
1
2
3
14
20
220
1K
RD(A)
SD(B)
SD(A)
Tx/Rx-
Tx/Rx+
78
F
96
7
+5 V
3K
16
RD(B)
Figure 2-15 RS-485 Network connections to a Watlow
EZ Zone Controller
Figure 16 shows an 4829A driving a single Watlow EZ Zone Controller
with it RS-485 output. The 4829A has an internal termination network
with a 220 ohm load resistor so it does not need external resistors. If the
internal W4 and W5 jumppers are installed (the gray links in Figure 2-16),
then no external jumpers are required and the EXZ Zone Controler can be
connected to either (A)-(B) signal pair.
98
99
CC
CA
CB
B5
D6
D5
EZ
8
AC Power
4829A
DE-9S
1
2
3
4
5
SD(A)
SD(B)
RD(A)
RD(B)
Vcc
1K
Tx/Rx-
Tx/Rx+
1K
GPIB
RS-232
78
F
96
Figure 2-16 4829A connection to an EZ Zone Controller
Содержание 4809A
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