Cirrus Logic CS5461A - Manual (Page 22)

CS5461A
22 DS661F3
5.13 Serial Port Overview
The CS5461A incorporates a serial port transmit and re-
ceive buffer with a command decoder that interprets
one-byte (8 bits) commands as they are received. There
are four types of commands; instructions, synchroniz-
ing, register writes and register reads (See
Section 5.14
Commands on page 23).
Instructions are one byte in length and will interrupt any
instruction currently executing. Instructions do not affect
register reads currently being transmitted.
Synchronizing commands are one byte in length and
only affect the serial interface. Synchronizing com-
mands do not affect operations currently in progress.
Register writes must be followed by three bytes of data.
register reads can return up to four bytes of data.
Commands and data are transferred most-significant bit
(MSB) first.
Figure 1 on page 11, defines the serial port
timing and required sequence necessary to write to and
read from the serial port receive and transmit buffer, re-
spectively. While reading data from the serial port, com-
mands and data can be simultaneously written. Starting
a new register read command while data is being read
will terminate the current read in progress. This is ac-
ceptable if the remainder of the current read data is not
needed. During data reads, the serial port requires input
data. If a new command and data is not sent, SYNC0 or
SYNC1 must be sent.
5.13.1 Serial Port Interface
The serial port interface is a “4-wire” synchronous serial
communications interface. The interface is enabled to
start excepting SCLKs when CS (Chip Select) is assert-
ed. SCLK (Serial bit-clock) is a Schmitt-trigger input that
is used to strobe the data on SDI (Serial Data In) into the
receive buffer and out of the transmit buffer onto SDO
(Serial Data Out).
If the serial port interface becomes unsynchronized with
respect to the SCLK input, any attempt to clock valid
commands into the serial interface may result in unex-
pected operation. The serial port interface must then be
re-initialized by one of the following actions:
- Drive the CS pin high, then low.
- Hardware Reset (drive RESET pin low, for at
least 10 µs).
- Issue the Serial Port Initialization Sequence,
which is 3 (or more) SYNC1 command bytes
(0xFF) followed by one SYNC0 command byte
(0xFE).
If a resynchronization is necessary, it is best to re-initial-
ize the part either by hardware or software reset (0x80),
as the state of the part may be unknown.