Echelon LONWORKS PLT-22, User Manual

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disabled, the threshold for the BIU signal is increased to 84dBµVrms to reduce the
possibility that power mains noise activates the BIU indicator. When the CENELEC
access protocol is disabled, an active BIU signal does not prevent the PLT-22
transceiver from transmitting. Connecting the BIU signal to an LED is most useful
when the CENELEC access protocol is enabled, since in this case the BIU signal
indicates when the PLT-22 transceiver's transmissions are restricted.
The PKD signal is active whenever a valid LonTalk
®
packet is being received by the
PLT-22 transceiver. The receive sensitivity of the transceiver is considerably greater
than that of the BIU indicator. The PKD signal will go active when the PLT-22
transceiver receives packets whose signal level is as small as 36dBµVrms. Thus it is
not uncommon for the PKD indicator to signal that a packet is present without the
BIU indicator turning on; this occurs in cases where the received packet signal
strength is less than the BIU threshold.
Both the BIU and PKD signals are driven directly by the PLT-22 transceiver’s DSP
processor. ESD protection diodes should be connected to these pins in applications
where the BIU and PKD signals drive LEDs that could be subject to ESD exceeding
2kV. In applications where the LEDs are surrounded by a metallic ground plane,
such as a hole in a grounded metal enclosure, the ESD diodes may not be necessary.
However, if a plastic or metal enclosure without a good ground connection is used,
then ESD diodes are needed to prevent damage to the PLT-22 transceiver. ESD
protection diodes include industry part types 1N4148 (thru-hole) and BAV99 (SMT).
Typical sources for BAV99 diodes include Motorola (BAV99LT1), National (BAV99),
and Diodes, Inc. (BAV99).
Neuron Chip Connections
The link between the Neuron Chip and the PLT-22 transceiver makes use of the
Neuron Chip's special-purpose mode interface. This interface requires that the CP
and ~RESET lines of the two devices be interconnected as shown in table 2.3.
Table 2.3 Neuron Chip and PLT-22 Transceiver Interconnections
Neuron Chip Pin PLT-22 Pin
CP0 7
CP1 6
CP2 5
CP3
Do not connect
CP4 4
~Reset 13
CLK1 10
The Neuron Chip and PLT-22 transceiver should be placed adjacent to one another
on the same printed circuit board. The length of the ~RESET and CP lines should be
kept to an absolute minimum and in no case should exceed 50mm (2"). In addition,
2-8 Using the PLT-22 Transceiver