Serial port overview, 1 commands, Cs5550 – Cirrus Logic CS5550 User Manual

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CS5550

DS630F1

4. SERIAL PORT OVERVIEW

The CS5550's serial port incorporates a state machine with transmit/receive buffers. The state machine
interprets 8-bit command words on the rising edge of SCLK. Upon decoding of the command word, the
state machine performs the requested command or prepares for a data transfer of the addressed register.
Request for a read requires an internal register transfer to the transmit buffer, while a write waits until the
completion of 24 SCLKs before performing a transfer. The internal registers are used to control the ADC's
functions. All registers are 24-bits in length.

The CS5550 is initialized and fully operational in its active state upon power-on. After a power-on, the de-
vice will wait to receive a valid command (the first 8-bits clocked into the serial port). Upon receiving and
decoding a valid command word, the state machine instructs the converter to either perform a system op-
eration, or transfer data to or from an internal register. The user should refer to the “Commands” section
to decode all valid commands.

4.1 Commands

All command words are 1 byte in length. Any 8-bit word that is not listed in this section should be considered an
illegal command word, and issuing any such illegal command word to the serial interface can result in unpredictable
operation of the CS5550. Commands that write to a register must be followed by 3 bytes of register data. Commands
that read data can be chained with other commands (e.g., while reading data, a new command can be sent to SDI
which can execute before the original read is completed). This allows for “chaining” commands.

4.1.1 Start Conversions

This command indicates to the state machine to begin acquiring measurements and calculating results. The device
has two modes of acquisition.

C =

Modes of acquisition/measurement
0 = Perform a single computation cycle
1 = Perform continuous computation cycles

4.1.2 SYNC0 Command

This command is the end of the serial port re-initialization sequence. The command can also be used as a NOP
command. The serial port is resynchronized to byte boundaries by sending three or more consecutive SYNC1 com-
mands followed by a SYNC0 command.

4.1.3 SYNC1 Command

This command is part of the serial port re-initialization sequence. The command also serves as a NOP command.