wts701 Winbond Electronics Corp America, wts701 Datasheet - Page 20

• Manufacturer Part Number: wts701
• Description: Winbond Single-chip Text-to-speech Processor
• Manufacturer: Winbond Electronics Corp America

WTS701
7.3.1 Command Classes
The SPI transactions to the WTS701 fall into four classes. The four classes represent variations in
how the command, and any associated data, is handled. The class of a command is defined by the
two most significant bits of the command byte. A summary of the command classes is given below
Class 0 Commands
These are commands that are executed irrespective of the state of the WTS701. That is, the
command will execute even if the device is busy or powered down. These commands are executed
internally by a hardware command interpreter. All commands not of class 0 require that the WTS701
be in a powered up state. Example of class 0 command is the Read Status (RDST) command.
Class 1 Commands
Class 1 commands require interpretation by the internal firmware of the WTS701. Class 1 commands
consist only of a command byte and command data byte. Any further data sent in a transaction is
ignored. Class 1 commands are most often used for setting a configuration register in the device or
sending commands that have no data such as the conversion pause (PAUS) command.
Class 2 Commands
Class 2 commands have associated data. After the command word, any data bytes following are
loaded into an internal FIFO buffer for processing. If this FIFO becomes full, the R/ B signal is
asserted (LOW) indicating that the host must pause data transfer. An alternative to monitoring the
R/ B line, the R/ B bit of the status register can be monitored instead (see subsection 7.3.2) or via the
RDST command. The R/ B bit cannot be used for intra-byte flow control, e.g. if a string of characters
is sent, only every other byte is checked.
Class 3 Commands
Class 3 commands have data to return to the host. The R/ B line will go to busy immediately following
the command word indicating that the WTS701 is fetching the requested data. Data is put into the
BCNT0 and BCNT1 (see subsection 7.3.4) registers and is read out in the two subsequent bytes after
R/ B is released. If more than two bytes are returned from the command, R/ B will again be asserted
until data is ready to read. The primary Class 3 commands are to read the contents of internal
configuration registers such as RREG command.
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