MRF39RA datasheet(38/72 Pages) MICROCHIP

38 / 72 page

MRF39RA

DS40001778B-page 38

 2015 Microchip Technology Inc.

4.5.5

HANDLING LARGE PACKETS

When Payload length exceeds FIFO size (66 bytes)

whether in fixed, variable or unlimited length packet

format, in addition to PayloadReady or CrcOk in Rx, the

FIFO interrupts/flags can be used as follows:

FIFO must be unfilled on the fly during Rx to prevent

FIFO overrun.

Start reading bytes from the FIFO when

FifoNotEmpty or FifoThreshold becomes set.

Suspend reading from the FIFO if FifoNotEmpty

clears before all bytes of the message have

been read

Continue to step 1 until PayloadReady

Read all remaining bytes from the FIFO either in

Rx or Sleep/Standby mode.

4.5.6

PACKET FILTERING

MRF39RA’s packet handler offers several mechanisms

for packet filtering, ensuring that only useful packets

are made available to the uC, reducing significantly

system power consumption and software complexity.

4.5.6.1

Sync Word-Based

Sync word filtering/recognition is used for identifying

the start of the payload and also for network

identification. As previously described, the sync word

recognition block is configured (size, error tolerance,

value) in RegSyncValue registers. This information is

used to filter packets in Rx.

Every received packet which does not start with this

locally configured sync word is automatically discarded

and no interrupt is generated.

When the sync word is detected, payload reception

automatically

starts

and

SyncAddressMatch

asserted.

4.5.6.2

Address-Based

Address

filtering

can

enabled

via

the

AddressFiltering bits. It adds another level of filtering

above sync word (i.e., sync must match first), typically

useful in a multi-node networks where a network ID is

shared between all nodes (sync word) and each node

has its own ID (address).

Two address-based filtering options are available:

AddressFiltering = 01: Received address field is

compared with internal register NodeAddress. If

they match, then the packet is accepted and

processed, otherwise it is discarded.

AddressFiltering = 10: Received address field is

compared with internal registers NodeAddress

and BroadcastAddress. If either is a match, the

received packet is accepted and processed, oth-

erwise it is discarded. This additional check with

a constant is useful for implementing broadcast

in a multi-node networks.

As address filtering requires a sync word match, both

features

the

same

interrupt

flag

SyncAddressMatch.

Note that the received address byte, as part of the

payload, is not stripped off the packet and is made

available in the FIFO.

4.5.6.3

Length-Based

In variable length Packet mode, PayloadLength must

be programmed with the maximum payload length

permitted. If received length byte is smaller than this

maximum, then the packet is accepted and processed,

otherwise it is discarded.

Note that the received length byte, as part of the

payload, is not stripped off the packet and is made

available in the FIFO.

To disable this function, the user must set the value of

the PayloadLength to 255.

Note:

AES decryption is not feasible on large

packets, since all Payload bytes need to

be in the FIFO at the same time to perform

decryption.

Note:

Sync word values containing 0x00 byte(s)

are forbidden.

MRF39RA Datasheet(PDF) 38 Page - Microchip Technology

MRF39RA Datasheet(HTML) 38 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

Datasheet Download

Link URL