Cirrus Logic CS5484 - Manual (Page 8)

CS5484
8 DS981F3
2.2.4 UART/SPI™ Serial Interface
The CS5484 provides five pins—SSEL, RX/SDI,
TX/SDO, CS, and SCLK—for communication between
a host microcontroller and the CS5484.
SSEL is an input that, when low, indicates to the
CS5484 to use the SPI port as the serial interface to
communicate with the host microcontroller. The SSEL
pin has an internal weak pull-up. When the SSEL pin is
left unconnected or pulled high externally, the UART
port is used as the serial interface.
2.2.5 SPI
The CS5484 provides a Serial Peripheral Interface
(SPI) that operates as a slave device in 4-wire mode
and supports multiple slaves on the SPI bus. The 4-wire
SPI includes CS, SCLK, SDI, and SDO signals.
CS is the chip select input for the CS5484 SPI port. A
high logic level de-asserts it, tri-stating the SDO pin and
clearing the SPI interface. A low logic level enables the
SPI port. Although the CS pin may be tied low for
systems that do not require multiple SDO drivers, using
the CS signal is strongly recommended to achieve more
reliable SPI communications.
SCLK is the serial clock input for the CS5484 SPI port.
Serial data changes as a result of the falling edge of
SCLK and is valid at the rising edge. The SCLK pin is a
Schmitt-trigger input.
SDI is the serial data input to the CS5484.
SDO is the serial data output from the CS5484.
The CS5484 SPI transmits and receives data MSB first.
Refer to
Switching Characteristics on page 14 and
Figure 7 on page 15 for more detailed information about
SPI timing.
2.2.6 UART
The CS5484 device contains an asynchronous,
full-duplex UART. The UART may be used in either
standard 2-wire communication mode (RX/TX) for
connecting a single device or 3-wire communication
mode (RX/TX/
CS ) for connecting multiple devices.
When connecting a single CS5484 device, CS should
be held low to enable the UART. Multiple CS5484
devices can communicate to the same master UART in
the 3-wire mode by pulling a slave CS pin low during
data transmissions. Common RX and TX signals are
provided to all the slave devices, and each slave device
requires a separate CS signal for enabling
communication to that slave. The multi-device UART
mode connections are shown in
Figure 2 .
Figure 2. Multi-device UART Connections
The multi-device UART mode timing diagram provides
the timing requirements for the CS control (see
Figure
8. Multi-Device UART Timing on Page 15).
The CS5484 UART operates in 8-bit mode, which
transmits a total of 10 bits per byte. Data is transmitted
and received LSB first, with one start bit, eight data bits,
and one stop bit.
Figure 3. UART Serial Frame Format
The baud rate is defined in the SerialCtrl register. After
chip reset, the default baud rate is 600, if MCLK is
4.096MHz. The baud rate is based on the contents of
bits BR[15:0] in the SerialCtrl register and is calculated
as follows:
BR[15:0] = Baud Rate x (524288/MCLK)
or
Baud Rate = BR[15:0] / (524288/MCLK)
The maximum baud rate is 512K if MCLK is 4.096MHz.
2.2.7 MODE Pin
The MODE pin must be tied to VDDA for normal
operation. The MODE pin is used primarily for factory
test procedures.
UART
MASTER
SLAVE 0
SLAVE 1
SLAVE N
CS
RX
TX
CS
RX
TX
CS
RX
TX
CS0
CS1
CSN
RX
TX
0 1 2 7 IDLE STOP 3 4 5 6 START
DATA
IDLE