NSAM266SAASLASHV datasheet(31/52 Pages) NSC

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20 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 2122)

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

2122 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

(ie 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

213 THE MASTER MICROWIRE INTERFACE

The CompactSPEECH’s Master MICROWIRE controller im-

plements the MICROWIREPLUS 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

2131 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

TLEE12584 – 29

FIGURE 2-5 Sequence of Activities during a MICROWIRE Byte Transfer

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