Echelon LonWorks Router - Manual (Page 48)

See the Series 5000 Chip Data Book for more information about the power and
ground requirements for a Series 5000 chip, including the Router 5000 and FT
Router 5000.
If your router uses a Series 3100 half-router for one of its sides, you can use a
low-dropout voltage regulator to provide power for the Series 5000 half-router (+5
V input from the Series 3100 router half power supply, and +3.3 V output for the
Router 5000 chip. See Connecting Half-Routers: Series 5000 and Series 3100 for
more information.
RST~
The RST~ pin is both an input and an output. As an input, the RST~ pin is
internally pulled high by a resistor. The RST~ pin becomes an output when any
of the following events occur:
• Internal LVI detects a low voltage condition
• Software reset initialization
• Watchdog Timer event (times out)
• Traps
In some cases it is desirable to use the input capability of the RST~ pin to allow
other devices to reset the Series 5000 half-router. 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 Series 5000
router 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 Series 5000 router’s
reset functions to operate reliably:
• 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 Series 5000 router’s
internal circuitry could result in anomalous behavior ranging from
applicationless errors to device failure.
• 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 (totaling ≤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 router chip’s RST~ pin.
• During board level in-circuit testing (ICT), the RST~ pin should be hard
wired to ground through a “pogo pin”.
Figure 16 shows an example reset circuit, where the A side and B side reset pins
are tied together.
38 LONWORKS Router Electrical Interfaces