Echelon LonWorks Router User Manual
Page 79

communication port (CP) or the I/O lines of the Router 5000 must be electrically
isolated.
The LPT-11 transceiver receives its clock input from the Router 5000 through its
CMOS input CLK pin. This pin is driven by the XOUT output of the Router
5000, buffered with a standard bus buffer/line driver that supports TTL-
compatible input and 5V CMOS output. Clock traces should be kept short (≤2
cm) to minimize noise coupling. In addition, a logic ground guard must be added
for the CLK trace to minimize clock noise and to help keep EMI levels low.
However, this ground guard should not be used as a ground source for digital
circuitry.
The LPT-11 transceiver can operate at 20, 10, or 5 MHz. When coupled to a
Router 5000, the LPT-11 transceiver operates at 10 MHz. The operating
frequency is automatically detected on the LPT-11 transceiver’s CLK pin.
Figure 35 shows the basic configuration for connecting a Router 5000 to an LPT-
11 Twisted-Pair Link Power Transceiver.
The major differences between connecting a Series 3100 Neuron Chip to an LPT-
11 transceiver (see the L
ON
W
ORKS
LPT-11 Link Power Transceiver User’s Guide)
and connecting a Router 5000 to an LPT-11 transceiver include:
•
The connection between the LPT-11 VCC pin and the Router 5000
VDD3V3 pin requires the addition of a low drop-out linear regulator to
convert the +5 V output from the LPT-11 transceiver to the +3.3 V input
for the Router 5000.
•
The connection between the LPT-11 TXD pin and the Router 5000 CP1
pin requires the addition of a non-inverting bus buffer/line driver that
supports TTL-compatible input and 5V CMOS output. The output of the
Router 5000 RST~ pin is also connected to the buffer/line driver to allow
the Router 5000 to propagate a device reset to the LPT-11 transceiver by
setting the buffer/line driver to a tri-state impedance state. An example
part for the buffer/line driver is an NXP 74AHCT1G126 bus buffer/line
driver.
•
The connection between the LPT-11 CLK pin and the Router 5000 XOUT
pin requires the addition of a standard (inverting or non-inverting) bus
buffer/line driver that supports TTL-compatible input and 5V CMOS
output.
L
ON
W
ORKS
Router User’s Guide
69