Rainbow Electronics AT76C551 - Manual (Page 19)

19
AT76C551
1612D–08/01
Encryption/
Decrytion Encryption and decryption is provided with the use of a secret key. Encryption and decryption
are carried out on-the-fly with minimal intervention from the processor. The encryption/decryp-
tion data are interchanged between the other Bluetooth low-level processing modules
automatically.
Authentication
Processing
Accelerator Processing-intensive authentication procedures are implemented in the hardware which
reduce the time for authentication key production.
Receiver Signal
Strength Indicator
(RSSI) This module provides a metric of the received signal strength of a Bluetooth transmission. It
uses an 8-bit A/D to read the RSSI value of the transceiver.
64-byte TX and RX
FIFOs A 64-byte Transmit and a 64-byte Receive FIFO are used to buffer data between the Blue-
tooth baseband and the ARM processor.
Baseband TX and
RX Processing
Sequencer Two dedicated sequencers are used, one for the Transmit direction and one for the Receive
direction, these automate the Bluetooth packet transactions.
These sequencers, in conjunction with firmware running on the ARM core, execute the link
control functions. The sequencer is used to free the ARM processor from the sequencing of
bit-level processing. The processing needed by the various Bluetooth packets differs from
packet type-to-packet type. The processing sequencers can be programmed according to the
different packet types and carry out the required processing functions without further ARM
processor intervention for the transmission of corresponding packet.
The baseband processor also eases the task of ensuring reliable data delivery. All bit-inten-
sive tasks are done in hardware. The ARM core configures the modules and reads the results.
Access code generation and correlation with received packet is carried out in hardware ensur-
ing minimal decoding delay. With the firmware reading the results of a successful packet
reception the HEC computation and header recognition is fully automated. The receive engine
is automatically configured according to the packet header and, when required, payload
header information, decodes the packet and stores it in the RX FIFO without further interven-
tion from the processor.
8-bit ADC Interface
for Bluetooth RX
Data An 8-bit external interface is used to connect an external analog-to-digital converter providing
the digital representation of the analog signal decoded by the transceiver during reception.
The analog signal is sampled at 4M samples per second requiring an external ADC capable of
handling this sample rate.
Automatic DC-
offset Cancellation
and Symbol
Recovery Modern low-cost transceivers used in FSK applications, employing open loop modulation
and/or demodulation together with limiter-discriminator detection at the receiver, produce out-
put baseband signals which suffer from moderate to severe DC-offset fluctuation. The useful
signal is a small fraction of the magnitude of the maximum DC-offset fluctuation. The number
of symbols available to a Bluetooth baseband controller for DC-offset compensation and sym-
bol timing recovery (STR) purposes are a mere 4 preamble bits, preceding the device access
code (DAC) in every packet. Fast symbol timing acquisition is a prerequisite to successful
decoding of the DAC and synchronization to the master device in a Bluetooth piconet. Due to
this fact and in order to comply with tight slot timing requirements, a state-of-the-art DC-offset
canceller, bit-symbol recovery circuit has been integrated. This module is capable of recover-
ing the original Bluetooth bitstream in the noisiest of environments.