NSAM266SA Datasheet, PDF (31/52 Pages) National Semiconductor (TI) – NSAM266SA CompactSPEECHTM Digital Speech Processor with Serial Flash Interface

2 0 Software (Continued)
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 (cleared to 0) after reset
and after a protocol time-out (See Section 2 12 2 )
The MWRQST signal is used as follows
1 The MWRQST signal is activated (cleared to 0) when the
status word is changed
2 The MWRQST signal remains active (0) until the
CompactSPEECH receives a GSW command
Figure 2-5 illustrates the sequence of activities during a
MICROWIRE data transfer
2 12 2 Interface Protocol Error Handling
Interface Protocol Time-Outs
Depending on the CompactSPEECH’s state if more than
20 ms – 30 ms elapse between two consecutive byte trans-
missions or two byte receptions within the same command
or return value after the MWRDY signal is asserted a time-
out event occurs and the CompactSPEECH 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 (clears it to 0)
4 Activates the MWRDY signal (clears 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 causes 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
The CompactSPEECH transmits a byte as an echo when it
receives the value 0xAA from the microprocessor Upon de-
tection of an error the CompactSPEECH activates the
MWRQST signal and sets the ERR COMM bit in the error
word
2 13 THE MASTER MICROWIRE INTERFACE
The CompactSPEECH’s Master MICROWIRE controller im-
plements the MICROWIRE PLUS interface in master mode
It enables the CompactSPEECH to control flash devices
Several devices may share the Master MICROWIRE chan-
nel This can be implemented by connecting device selec-
tion signals to general purpose output ports
2 13 1 Master MICROWIRE Data Transfer
The Signals
The Master MICROWIRE controller’s signals are the Master
MICROWIRE serial CLocK (MMCLK) the Master MICRO-
WIRE serial Data OUT (MMDOUT) signal and the Master
MICROWIRE serial Data In (MMDIN) signal
The Master MICROWIRE controller can handle up to four
flash devices The CompactSPEECH uses the signals
CS0 – CS3 as required for the number of devices in use as
device chip-select signals
The Clock for Master MICROWIRE Data Transfer
Before data can be transferred the transfer rate must be
determined and set The rate of data transfer on the Master
MICROWIRE is determined by the Master MICROWIRE se-
rial CLocK (MMCLK) signal This rate is the same as the
Codec CLocK (CCLK) signal As long as the Master MICRO-
WIRE is transferring data the codec interface must be en-
abled and its sampling rate should not be changed
FIGURE 2-5 Sequence of Activities during a MICROWIRE Byte Transfer
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