BC9824 Datasheet, PDF (7/22 Pages) Holtek Semiconductor Inc – Low Power High Performance Low Power High Performance

BC9824
Packet Processing
Packet Format
The packet format has a preamble, address, packet
control, payload and CRC field.
• 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.
• 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.
No other data pipe can receive data until a com-
plete 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.
• 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, BC9824 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 by
setting the EN_DYN_ACK bit. When you use this
option, the PTX goes directly to standby-I mode
after transmitting the packet and the PRX does
not transmit an ACK packet when it receives the
packet.
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
Packet Format
NO_ACK 1 bit
Rev. 1.00
7
October 20, 2015