RF70 Datasheet, PDF (9/25 Pages) –

5.1.1 Preamble
The preamble is a bit sequence used to detect 0
and 1 levels in the receiver. The preamble is
one byte long and is either 01010101 or
10101010. If the first bit in the address is 1 the
preamble is automatically set to 10101010 and
if the first bit is 0 the preamble is
automatically set to 01010101. This is done to
ensure there are enough transitions in the
preamble to stabilize the receiver.
5.1.2 Address
This is the address for the receiver. An address
ensures that the packet is detected by the target
receiver. The address field can be configured
to be 3, 4, or 5 bytes long by the AW register.
The PRX device can open up to six data pipes
to support up to six PTX devices with unique
addresses. All six PTX device addresses are
searched simultaneously. In PRX side, the data
pipes are enabled with the bits in the
EN_RXADDR register. By default only data
pipe 0 and 1 are enabled.
Each data pipe address is configured in the
RX_ADDR_PX registers.
Each pipe can have up to 5 bytes configurable
address. Data pipe 0 has a unique 5 byte
address. Data pipes 1-5 share the 4 most
significant address bytes. The LSB byte must
be unique for all 6 pipes.
To ensure that the ACK packet from the PRX
is transmitted to the correct PTX, the PRX
takes the data pipe address where it received
the packet and uses it as the TX address when
transmitting the ACK packet.
On the PRX the RX_ADDR_Pn, defined as
the pipe address, must be unique. On the PTX
the TX_ADDR must be the same as the
RX_ADDR_P0 on the PTX, and as the pipe
address for the designated pipe on the PRX.
RF70 V1.0
No other data pipe can receive data until a
complete packet is received by a data pipe that
has detected its address. When multiple PTX
devices are transmitting to a PRX, the ARD
can be used to skew the auto retransmission so
that they only block each other once.
5.1.3 Packet Control
When Dynamic Payload Length function is
enabled, the packet control field contains a 6
bit payload length field, a 2 bit PID (Packet
Identity) field and, a 1 bit NO_ACK flag.
 Payload length
The payload length field is only used if the
Dynamic Payload Length function is enabled.
 PID
The 2 bit PID field is used to detect whether
the received packet is new or retransmitted.
PID prevents the PRX device from presenting
the same payload more than once to the MCU.
The PID field is incremented at the TX side
for each new packet received through the SPI.
The PID and CRC fields are used by the PRX
device to determine whether a packet is old or
new. When several data packets are lost on the
link, the PID fields may become equal to the
last received PID. If a packet has the same PID
as the previous packet, RF70 compares the
CRC sums from both packets. If the CRC
sums are also equal, the last received packet is
considered a copy of the previously received
packet and discarded.
 NO_ACK
The NO_ACK flag is only used when the auto
acknowledgement feature is used. Setting the
flag high, tells the receiver that the packet is
not to be auto acknowledged.
The PTX can set the NO_ACK flag bit in the
Packet Control Field with the command:
W_TX_PAYLOAD_NOACK.However, the
function must first be enabled in the
FEATURE register bysetting the
EN_DYN_ACK bit. When you use this option,
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