Echelon 14315R, User Manual

Page: 41 / 99

LonWorks Router User’s Guide 31
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Traps
In some cases it is desirable to use the input capability of the RST~ pin to allow
other devices to reset the Router 5000. Examples of external devices that can be
used for this purpose include push button switches, microcontrollers, and
external low-voltage detectors.
Important: If the proper external reset circuitry is not used, the Router 5000
can become applicationless or unconfigured. The applicationless or unconfigured
state occurs when the checksum error verification routine detects corruption in
memory which could have been falsely detected because of an improper reset
sequence.
The following guidelines must be followed in order for the Router 5000’s reset
functions to operate reliably:
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Any device connected to the RST~ pin must have an open-drain (or
equivalent) output. If an external device were to actively drive the RST~
pin high, contention between that device and the Router 5000’s internal
circuitry could result in anomalous behavior ranging from applicationless
errors to device failure.
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A capacitor should be connected between RST~ and ground to provide
noise immunity. The value of this capacitor should be at least 100 pF,
and must not exceed 1000 pF. For even greater noise immunity, two
capacitors (t otaling ≤1000 pF) can be used, with one connected from the
RST~ pin to ground and the other from RST~ to V
DD33
. These capacitors
should be located within 5 mm of the Series 5000 chip’s RST~ pin.
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During board level in-circuit testing (ICT), the RST~ pin should be hard
wired to ground through a “pogo pin”.
Figure 15 on page 32 shows an example reset circuit, where the A side and B
side reset pins are tied together.
If one of the router halves uses a Router 5000 chip and the other half uses a
Series 3100 chip, you need to modify the reset circuit shown in Figure 15 to
account for the different voltage standards (3.3 V for the Router 5000 and 5 V for
the Series 3100). Contact Echelon Support for additional information.