Echelon LonWorks Router - Manual (Page 54)

Figure 20 shows example RX and TX network activity indicator circuits for a
Router 5000 half-router connected to an EIA-485 transceiver. You can use the
same network activity circuits for other transceiver types, although other
transceiver types have different connections to the Router 5000. See Developing
a Router with the Router 5000 Chip for more information about connecting
external transceivers to a Router 5000.
Both network indicator circuits use non-inverting bus buffer/line drivers that
support TTL-compatible input and 5V CMOS output (assuming a transceiver
that requires 5 V supply voltage). Both circuits also use standard rectifying
diodes; if your transceiver uses 3.3 V supply voltage, consider replacing these
diodes with Schottkey diodes.
For the TX network indicator, the Router 5000 CP2 pin (TX Enable) is low when
idle. However, for the RX network indicator, the Router 5000 CP0 pin (RX)
retains its state from the end of the previous received bit, and thus can be high or
low when idle.
TLC372
CP0
CP1
CP3
CP2
CP4
32 RX
34 TX
38
37 TXEN
39
Router 5000
VDD3V3
+3.3 V
8
10k
10k
+3.3 V
500 BAV99
0.1 µF
1M
604
TLC372
0.1 µF
604 BAV99 1 µF
BAV99 1M
R
RE~
DE
D
A
B
VDD
GND
EIA-485 Transceiver
+5 V
0.1 µF
12V
12V
MUR115
(x4)
A
B
RX Activity Indicator
TX Activity Indicator
+5 V +5 V
+5 V +5 V
500
Figure 20. RX and TX Network Activity Indicator Circuits – Router 5000
When packets are transmitted, the TX network activity LED is active for the
duration of the entire data transmission. When packets are received, the RX
network activity LED is active for each bit received, and inactive between bytes.
For both circuits, the approximate time constant for LED visibility is 100 ms.
44 LONWORKS Router Electrical Interfaces