NSAM265SR Datasheet, PDF (13/58 Pages) National Semiconductor (TI) – CompactSPEECH Digital Speech Processors

2 0 Functional Description (Continued)
The MWRDY signal is used as follows
1 An active (0) MWRDY signal signals the microcontroller
that the last eight bits of data transferred to from the
CompactSPEECH were accepted and processed (see
below)
2 The MWRDY signal is deactivated (set to 1 by the Com-
pactSPEECH) after 8 bits of data were transferred to
from the CompactSPEECH The bit is set following the
falling edge of the eighth MWCLK clock-cycle
3 The MWRDY signal is activated (by the Compact-
SPEECH) when the CompactSPEECH is ready to receive
the first parameter byte (if there are any parameters) and
so on till the last byte of parameters is transferred An
active MWRDY signal after the last byte of parameters
indicates that the command was parsed and (if possible)
executed If that command has a return value the micro-
controller must read the value before issuing a new com-
mand
4 When a return value is transmitted the MWRDY signal is
deactivated after every byte and activated again when
the CompactSPEECH is ready to send another byte or to
receive a new command
The MWRDY signal is activated (set to 0) after reset and
protocol timeout (See Section 2 3 3 )
The MWRQST signal is used as follows
1 The MWRQST signal is activated (0) when the status
word is changed
2 The MWRQST signal remains active (0) until the Com-
pactSPEECH receives a GSW command
Figure 2-2 illustrates the sequence of activities during a
MICROWIRE data transfer
2 3 3 Interface Protocol Error Handling
Interface Protocol Time-Outs
When the time between two consecutive byte transmis-
sions or bytes reception within the same command or re-
turn value exceeds two milliseconds after the MWRDY sig-
nal is asserted a time-out event occurs and the Compact-
SPEECH responds as follows
1 Sets the error bit in the status word to 1
2 Sets the EV TIMEOUT bit in the error word to 1
3 Activates the MWRQST signal (sets it to 0)
4 Activates the MWRDY signal (sets it to 0)
5 Waits for a new command (After a time-out occurs the
microcontroller must wait at least four milliseconds before
issuing the next command )
Echo Mechanism
The CompactSPEECH echoes back to the microcontroller
all the bits received by the CompactSPEECH Upon detec-
tion of an error in the echo the microcontroller should stop
the protocol clock which eventually will cause a time-out
error (i e ERR TIMEOUT bit is set in the error word)
Note When a command has a return value the CompactSPEECH transmits
bytes of the return value instead of the echo value
When the CompactSPEECH is transmitting a byte it ex-
pects to receive the value 0xAA as an echo Upon detection
of an error the CompactSPEECH activates the MWRQST
signal and sets the ERR COMM bit in the error word
2 4 CODEC INTERFACE
The CompactSPEECH provides an on-chip interface to a
serial codec The interface supports codec operation in long
or short-frame formats The format is selected with the CFG
command
The codec interface uses four signals CDIN CDOUT
CCLK and CFS0
Data is transferred to the codec through the CDOUT pin
Data is read from the codec through the CDIN pin
Data transfer between the CompactSPEECH and the serial
codec starts by the CompactSPEECH asserting (high) the
CFS0 frame sync signal After one clock cycle the Com-
pactSPEECH de-asserts CFS0 data from the Compact-
SPEECH is sent to the codec through CDOUT and simulta-
neously data from the codec is sent to the Compact-
SPEECH through CDIN
FIGURE 2-2 Sequence of Activities During a MICROWIRE Byte Transfer
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