RFM DNT500 Series, Integration Manual, Page: 22 / 43

DNT500
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2008 by RF Monolithics, Inc. 18 M-0500-0000 Rev D
3.5 Interfacing to 5 V Logic Systems
All logic signals including the serial ports on the DNT500 are 3.3 V signals. To interface
to 5 V signals, the resistor divider network shown below must be placed between the 5 V
signal outputs and the DNT500 signal inputs. The output voltage swing of the DNT500
3.3 V signals is sufficient to drive 5 V logic inputs.
5 V
L o g i c
D N T 5 0 0
2 . 2 K
4 . 3 K
3.6 Power-On Reset Requirements
The DNT500 has an internal reset circuit that generates and maintains the DNT500 in a
reset state until the power supply voltage reaches 3.3 volts for 100 milliseconds. This re-
set circuit protects the radio and non-volatile memory from brown-out voltage conditions.
If devices that communicate with the DNT500 have shorter reset periods, an allowance
must be made to allow the DNT500 to come out of reset. Commands and data sent before
the DNT500 is out of reset will be ignored.
3.7 Analog RSSI Output
Pin 4 on the DNT500 provides a 0.3 to 3.0 V output proportional to received signal
strength in dB, as follows:
V
RSSI
= 0.03*S
RF
+ 3.6
Where:
V
RSSI
is the RSSI output in volts, over the range of 0.3 to 3.0 V
S
RF
is the RF signal strength in dBm, over the range of -110 to -20 dBm
The analog RSSI output on a DNT500 remote represents the signal strength of the last
base station transmission received. The RSSI output on a base station represents the sig-
nal strength of the last remote transmission heard.
3.8 Mounting and Enclosures
DNT500 radio modules are mounted by reflow soldering them to a host circuit board.
DNT500P modules are mounted by plugging their pins into a set of mating connectors on
the host circuit board. Refer to the DNT500 data sheet for a suitable solder reflow profile
and details of the connectors for the DNT500P.
DNT500 radio module enclosures must be made of plastics or other materials with low
RF attenuation to avoid compromising antenna performance. Metal enclosures are not
suitable as they will block antenna radiation and reception. Outdoor enclosures must be
water tight, such as a NEMA 4X enclosure.