Rainbow Electronics AT76C551 - Manual (Page 18)

18
AT76C551
1612D–08/01
The memory interface supports two ports for efficient use of the memory unit. Each port pro-
vides access to all memories independently of the other. A round-robin priority scheme is used
when both ports require access to the same memory. One port is dedicated to the ARM inter-
face while the other can be used by either the PCMCIA interface or the USB interface. The
selection is determined by the PC_OR_UN pin.
PCMCIA Interface
Unit The PCMCIA interface unit implements a PCMCIA 2.1/JEIDA 4.2 compatible 8-bit wide PC-
card front-end interface. The PCMCIA interface unit provides the host with master access to
internal/external SRAM and external Flash memory. The PCMCIA interface unit contains a
number of general purpose registers to allow configuration and/or status information exchange
between the host and Bluetooth firmware. Moreover, the PCMCIA interface unit provides the
host and the ARM core with the capability to raise interrupts to each other.
Consequently, the host driver software uses the PCMCIA interface unit to exchange configura-
tion information, to monitor operation, to receive network indications and to transfer network
data from/to network data buffers in SRAM.
Baseband
Processor The baseband processor unit carries out the low-level Bluetooth link functions. This unit has
been designed to automatically handle many time-critical physical network management tasks
used by the Bluetooth link control.
Bluetooth Clock
and Internal
Hardware Timers A 28-bit counter running at 3.2 kHz provides the timing signals required for the baseband pro-
cessing. Also other timers are included which provide general purpose interrupts or determine
the timing of specific transceiver programming events.
Frequency
Hopping
Sequence
Generator The frequency hopping sequence generator chooses the correct hop frequency depending on
the Bluetooth clock, the device address and the device mode.
Access Code
Generation and
Detection This module generates the correct access code for access to other Bluetooth devices from the
corresponding Lower Address Part (LAP) of the utilized Bluetooth Device address. A correla-
tor is used to detect a Bluetooth transmission with a valid access code.
Forward Error
Correction (FEC) Two types of forward error correction are used. The first type is a simple 3-times repetition
code where each bit is repeated three times. Majority decision decoding is used in the
receiver.
The second type of code is a (15,10) shortened Hamming code. The data is divided into 10-bit
blocks. Each block is allocated a 15-bit code word. This code can correct all single-bit errors
while it can detect double bit errors in each code word.
Header Error
Check (HEC) Dedicated header error generation and checking is provided to guarantee correct decoding of
the important information included in the header. The generator calculates the HEC field in the
header of a transmitted Bluetooth packet while the HEC detects corrupted packet headers.
Cyclic
Redundancy
Generation and
Check (CRC) A 16-bit CRC is used to protect the payload data transmitted using certain types of
Bluetooth packets. During transmission, the CRC is automatically generated and appended at
the end of the packet. Checking for received BT packets is a fully automated fund of the CRC
in the ARM Core. It is a simple matter of checking the corresponding CRC status bit.