CS5461

DS546PP2

29

6. SERIAL PORT OVERVIEW

The CS5461's serial port incorporates a state machine with transmit/receive buffers. The state machine in-

terprets 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 comple-

tion of 24 SCLKs before performing a transfer. The internal registers are used to control the ADC's func-

tions. All registers are 24-bits in length.

The CS5461 is initialized and fully operational in its active state upon power-on. After a power-on, the

device 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

operation, or transfer data to or from an internal register.

6.1 Commands

All command words are 1 byte in length. Any 8-bit word that is not listed in this section is considered an invalid com-

mand word. 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).

6.1.1 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

6.1.2 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.

6.1.3 SYNC1 Command

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

B7

B6

B5

B4

B3

B2

B1

B0

1110

C

000

B7

B6

B5

B4

B3

B2

B1

B0

11111110

B7

B6

B5

B4

B3

B2

B1

B0

11111111