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

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.

ORKS

Router User’s Guide