NSAM266SAASLASHV datasheet(30/52 Pages) NSC

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20 Software (Continued)

The CompactSPEECH MICROWIRE interface implements

the MICROWIREPLUS interface in slave mode with an ad-

ditional ready signal It enables a microcontroller to inter-

face efficiently with the CompactSPEECH application

The microcontroller is the protocol master and provides the

clock for the protocol

The CompactSPEECH supports

clock rates of up to 400 kHz This transfer rate refers to the

bit transfer the actual throughput is slower due to byte pro-

cessing by the CompactSPEECH and the microcontroller

Communication is handled in bursts of eight bits (one byte)

In each burst the CompactSPEECH is able to receive and

transmit eight bits of data After eight bits have been trans-

ferred an internal interrupt is issued for the Compact-

SPEECH to process the byte or to prepare another byte for

sending In parallel the CompactSPEECH sets MWRDY to

1 to signal the microcontroller that it is busy with the byte

processing Another byte can be transferred only when the

MWRDY signal is cleared to 0 by the CompactSPEECH

When the CompactSPEECH transmits data it expects to

receive the value 0xAA before each transmitted byte The

CompactSPEECH reports any status change by clearing the

MWRQST signal to 0

If a parameter of a CompactSPEECH command is bigger

than one byte the microcontroller should transmit the Most

Significant Byte (MSB) first If a return value is bigger than

one byte the CompactSPEECH transmits the MSB first

212 SIGNAL DESCRIPTION

The following signals are used for the interface protocol

Input and output are relative to the CompactSPEECH

INPUT SIGNALS

MWDIN

MICROWIRE Data In Used for input only for transferring

data from the microcontroller to the CompactSPEECH

MWCLK

This signal serves as the synchronization clock during com-

munication One bit of data is transferred on every clock

cycle The input data is available on MWDIN and is latched

on the clock rising edge The transmitted data is output on

MWDOUT on the clock falling edge The signal should re-

main low when switching MWCS

MWCS

MICROWIRE Chip Select The MWCS signal is cleared to 0

to indicate that the CompactSPEECH is being accessed

Setting MWCS to 1 causes the CompactSPEECH to start

driving MWDOUT with bit 7 of the transmitted value Setting

the MWCS signal resets the transfer-bit counter of the pro-

tocol so the signal can be used to synchronize between the

CompactSPEECH and the microcontroller

To prevent false detection of access to the Compact-

SPEECH due to spikes on the MWCLK signal use this chip

select signal and toggle the MWCLK input signal only when

the CompactSPEECH is accessed

OUTPUT SIGNALS

MWDOUT

MICROWIRE Data Out Used for output only for transferring

data from the CompactSPEECH to the microcontroller

When the CompactSPEECH receives data it is echoed back

to the microcontroller on this signal unless the received

data is 0xAA In this case the CompactSPEECH echoes a

command’s return value

MWRDY

MICROWIRE Ready When active (0) this signal indicates

that the CompactSPEECH is ready to transfer (receive or

transmit) another byte of data

This signal is set to 1 by the CompactSPEECH after each

byte transfer has been completed It remains 1 while the

CompactSPEECH is busy reading the byte writing the next

byte or executing the received command (after the last pa-

rameter has been received) MWRDY is cleared to 0 after

reset

For proper operation after a hardware reset this signal

should be pulled up

MWRQST

MICROWIRE Request When active (0) this signal indicates

that new status information is available MWRQST is deacti-

vated (set to 1) after the CompactSPEECH receives a GSW

(Get Status Word) command from the microcontroller After

reset this signal is active (0) to indicate that a reset oc-

curred MWRQST unlike all the signals of the communica-

tion protocol is an asynchronous line that is controlled by

the CompactSPEECH firmware

2121 Signal Use in the Interface Protocol

After reset both MWRQST and MWRDY are cleared to 0

The MWRQST signal is activated to indicate that a reset

occurred The EV

RESET bit in the status register is used

to indicate a reset condition

The GSW command should be issued after reset to verify

that the EV

RESET event occurred and to deactivate the

MWRQST signal

While the MWCS signal is active (0) the CompactSPEECH

reads data from MWDIN on every rising edge of MWCLK

CompactSPEECH also writes every bit back to MWDOUT

This bit is either the same bit which was read from MWDIN

(in this case it is written back as a synchronization echo

after some propagation delay) or it is a bit of a value the

CompactSPEECH transmits to the microcontroller (in this

case it is written on every falling edge of the clock)

When a command has more than one parameterreturn-val-

ue the parametersreturn-values are transmitted in the or-

der of appearance If a parameterreturn-value is more than

one byte long the bytes are transmitted from the most sig-

nificant to the least significant

The MWRDY signal is used as follows

1 Active (0) MWRDY signals the microcontroller that the

last eight bits of data transferred tofrom the voice mod-

ule were accepted and processed (see below)

2 The MWRDY signal is deactivated (set to 1 by the

CompactSPEECH) after 8-bits of data were transferred

tofrom the CompactSPEECH The bit is set following the

falling edge of the eighth MWCLK clock-cycle

3 The MWRDY signal is activated (cleared to 0) by the

CompactSPEECH when it is ready to receive the first pa-

rameter 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 microcontroller

must read the value before issuing a new command

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