RFM70
The PTX device stays in TX mode until it
finishes transmitting the current packet. If CE
= 0 it returns to standby-I mode. If CE = 1, the
next action is determined by the status of the
TX FIFO. If the TX FIFO is not empty the
PTX device remains in TX mode, transmitting
the next packet. If the TX FIFO is empty the
PTX device goes into standby-II mode.
If the auto retransmit is enabled (EN_AA=1)
and
auto
acknowledge
is
required
(NO_ACK=0), the PTX device will enter TX
mode from standby-I mode when ARD
elapsed and number of retried is less than
ARC.
PRX device (PRIM_RX=1)
The PRX device will enter TX mode from RX
mode only when EN_AA=1 and NO_ACK=0
in received packet to transmit acknowledge
packet with pending payload in TX FIFO.
V1.0
set high. Or PRX device can enter this mode
from TX mode after transmitting an
acknowledge packet when EN_AA=1 and
NO_ACK=0 in received packet.
In this mode the receiver demodulates the
signals from the RF channel, constantly
presenting the demodulated data to the packet
processing engine. The packet processing
engine continuously searches for a valid
packet. If a valid packet is found (by a
matching address and a valid CRC) the
payload of the packet is presented in a vacant
slot in the RX FIFO. If the RX FIFO is full,
the received packet is discarded.
The PRX device remains in RX mode until the
MCU configures it to standby-I mode or
power down mode.
In RX mode a carrier detection (CD) signal is
available. The CD is set to high when a RF
signal is detected inside the receiving
frequency channel. The internal CD signal is
filtered before presented to CD register. The
RF signal must be present for at least 128 µs
before the CD is set high.
PTX device (PRIM_RX=0)
The PTX device will enter RX mode from TX
mode only when EN_AA=1 and NO_ACK=0
to receive acknowledge packet.
4.6
RX Mode
PRX device (PRIM_RX=1)
The RX mode is an active mode where the
RFM70 radio is configured to be a receiver.
To enter this mode from standby-I mode, the
PRX device must have the PWR_UP bit set
high, PRIM_RX bit set high and the CE pin
5
Packet Processing
5.1
Packet Format
The packet format has a preamble, address, packet control, payload and CRC field.
Preamble 1 byte
Address 3~5 byte
Packet Control 9/0 bit Payload 0~32 byte
CRC 2/1 byte
Payload Length 6 bit
PID 2 bit
NO_ACK 1 bit
Figure 5 Packet Format
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8
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