RFW-D100 Vishay, RFW-D100 Datasheet - Page 15

• Manufacturer Part Number: RFW-D100
• Manufacturer: Vishay

Specifications of RFW-D100

• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Package Type: LQFP
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (max): 3.6V
• Lead Free Status / Rohs Status: Supplier Unconfirmed

The address field in each incoming packet is
compared to NET_ID byte and NODE_ID byte. If one
of the above comparisons fails, then the packet is
discarded and the MCU will not be aware of it.
NET_ID and NODE_ID are both one byte. Their values
are stored in NIR and BIR registers accordingly. The
byte to which they are compared is set by LCR
register, i.e. their location in the packet header is
determined in the LCR register.
NET_ID location in the packet header must always
be before NODE_ID location.
Each
independently (PPR register).
NET_ID is targeted to be a filter on the network
address. It is supposed to be common for all nodes in
the network.
NODE_ID is targeted to be a filter on the specific node
address. It is supposed to be unique to each node in
the network.
The purpose of these filters is to save MCU power and
to reduce its load. In a multi-node network, a node can
filter all packets that are not sent to it, while in a
multi-network environment, a node can filter packets
from other RFWaves networks.
In certain networks, a multicast ability inside the
network is required. Even if NODE_ID filter is applied,
addresses ‘111111XX’ (where ‘X’ represents do not
care) in NODE_ID filter are preserved for multicast
transmissions. NODE_ID filter will not discard those 4
addresses in any case.
CARRIER SENSE
Carrier sense protocols are protocols in which a node
(station) listens to the common channel before it starts
transmitting. The
transmissions in order to avoid collision that might
block its own transmission. In a wider perspective, a
network that applies carrier sense protocol utilizes the
channel bandwidth more efficiently. A more efficient
network enables lower power consumption to each
node, shorter delay, and higher probability of reaching
destination to each packet.
The RFW-D100 uses two complimentary techniques in
order to achieve very robust carrier sense abilities. On
the one hand, it has an internal comparator that gives
it rough Radio Signal Strength Indicator (RSSI). The
RSSI enables the RFW-D100 to identify any strong
transmission that with good probability will block its
transmission. On the other hand, it has an internal
implementation of RFWaves Network Carrier Sense
algorithm. The second case enables it to avoid
collisions with other RFWaves stations on its network
or from other networks in the area.
Document Number 84675
Rev. 1.1, 22-Jan-07
of
them
can
node tries
be
enabled
For more information please contact: [e-mail]
to identify other
or
disabled
While the carrier sense status bits in SSR (CS and
COMP_IN) tell the MCU when not to transmit, the two
interrupt CS and LINK_DIS gives the MCU a flag when
to transmit. LINK_DIS will be invoked whenever any
transmission has ended, while CS interrupt will be
invoked only when an RFWaves transmission has
ended. An application of course, can use some of the
above mechanisms and not all of them - according to
its needs.
A more comprehensive discussion on how to
implement a CSMA protocol using the RFWaves
chipset is given in the “CSMA Protocol for Wireless
Keyboard and Mouse” document.
RSSI - RADIO SIGNAL STRENGTH INDICA-
TOR (COMPARATOR)
The purpose of the RSSI mechanism is to identify
strong transmissions in the area of the RFW-D100.
In general, the RFW-D100, using an internal
comparator, detects transmissions whose received
power exceeds a certain threshold. An external
resistor sets the threshold value. When a strong
transmission is identified, there is no use in starting to
transmit a new packet, since it is highly probable that it
will be blocked.
SCR1(5) (COMP_EN) enables/disables the use of the
comparator/RSSI.
The comparator output is given in SSR(7) – COMP_IN.
A more detailed description is given in Appendix A –
Radio Signal Strength Indicator (RSSI).
INTER/INTRA-RFWAVES NETWORKS CARRI-
ER SENSE
The RFW-D100 implements a carrier sense algorithm
that identifies similar RFWaves networks. The
algorithm uses the RFWaves special bit structure. This
mechanism enables the MCU to avoid collisions with
other nodes in its network or other networks in its area.
Even if the RSSI did not identify other transmissions, it
does not want to collide with other transmissions in the
network, since the network efficiency will decrease.
This will result in higher power consumption or even, in
extreme cases, prevent the transfer of all requested
packets.
The RFWaves network carrier sense mechanism
helps the MCU in two ways:
• Detecting transmission of a node from its network,
• Detecting transmission of a node from a similar
if it has started listening in the middle of the packet
(a PREAMBLE or a NET_ID will be recognized).
network in the area (different PREAMBLE or
NET_ID).
Vishay RFWaves
RFW-D100
www.vishay.com
15