XR18W753
8
SINGLE CHIP 868MHZ TO 956MHZ RF TRANSCEIVER REV. 1.0.0
2.0 PRODUCT DESCRIPTION
2.1 Radio Frequency Standards
The XR18W753 is designed to operate in licensed-free European 868 MHz SRD, North American / Australian
915 MHz ISM, and 950 - 956 MHz bands.
2.2 Transmitter Block
The transmitter block is a direct-up-conversion I/Q modulator consisting of D/A converters, interpolation filters,
balanced I/Q mixers and a power amplifier.
2.3 Receiver Block
The receiver is a Low-IF digital receiver consisting of a low-noise amplifier (LNA), I/Q mixers, IF filters, variable
gain amplifiers, and A/D converters.
2.4 Modem Block
The modem block is a Direct-Sequence-Spread-Spectrum (DSSS) O-QPSK digital modem with built-in
automatic gain control (AGC), Physical Layer Management Entity (PLME), Frame Check Sum (FCS)
computation, and Cyclical Redundancy Check (CRC) hardware.
2.5 Supporting Block
The supporting block in the XR18W753 includes voltage/current reference, supply voltage stabilizer, and
crystal oscillator.
2.6 Baseband Microcontroller Interface
Interface to the XR18W753 can easily be made via the I
2
C bus as in the XR18W750 baseband microcontroller.
All internal registers and data buffers are accessible via this bus. A 16MHz CMOS clock is provided to the
microcontroller, eliminating the cost of an extra clock or crystal.
2.6.1 I
2
C-bus Interface
The I
2
C-bus interface is compliant with the Standard-mode and Fast-mode I
2
C-bus specifications. The I
2
C-
bus interface consists of two lines: serial data (SDA) and serial clock (SCL). In the Standard-mode, the serial
clock and serial data can go up to 100 kbps and in the Fast-mode, the serial clock and serial data can go up to
400 kbps. The first byte sent by an I
2
C-bus master contains a start bit (SDA transition from HIGH to LOW
when SCL is HIGH), 7-bit slave address and whether it is a read or write transaction. The next byte is the sub-
address that contains the address of the register to access. The XR18W751 responds to each write with an
acknowledge (SDA driven LOW by XR18W751 for one clock cycle when SCL is HIGH). If the TX FIFO is full,
the XR18W751 will respond with a negative acknowledge (SDA driven HIGH by XR18W751 for one clock
cycle when SCL is HIGH) when the CPU tries to write to the TX FIFO. The last byte sent by an I
2
C-bus master
is a stop bit (SDA transition from LOW to HIGH when SCL is HIGH). For complete details, see the I
2
C-bus
specifications.
F
IGURE 5. I
2
C START AND STOP CONDITIONS
SDA
SCL
S
P
START condition
STOP condition
