NSAM265SF datasheet(12/58 Pages) NSC

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20 Functional Description (Continued)

TLEE12378 – 4

FIGURE 2-1 Recommended Power-On Reset Circuit

23 THE SERIAL MICROWIRE INTERFACE

The CompactSPEECH supports the MICROWIRE synchro-

nous serial communication protocol The communication

protocol used by the CompactSPEECH is an extension of

this protocol scheme The microcontroller is the protocol

master and provides the clock for the protocol The Com-

pactSPEECH supports clock rates of up to 400 kHz This

transfer rate refers to the bit transfer the actual throughput

is slower due to byte processing 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 (1) the

MWRDY signal to signal the microcontroller that it is busy

with the byte processing Another byte can be transferred

only when the MWRDY signal is asserted (0) by the Com-

pactSPEECH When the CompactSPEECH transmits data it

expects to receive the value 0xAA as an echo after each

transmitted byte The CompactSPEECH reports any status

change by asserting the MWRQST signal (0)

If a parameter of a CompactSPEECH command is bigger

than one byte the Most Significant Byte (MSB) should be

transmitted first by the microcontroller If a return value is

bigger than one byte the MSB is transmitted first by Com-

pactSPEECH

Note

Although the CompactSPEECH does not enforce a lower limit on the

bit transfer rate the time between bytes within the same command

must not exceed 2 ms

231 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 host 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 asserted (0)

to indicate that the CompactSPEECH is accessed Assert-

ing the MWCS causes the CompactSPEECH to start driving

the MWDOUT with bit 7 of the transmitted value Negating

the signal resets the transfer-bit counter of the protocol so

it can be used as a synchronization between the Compact-

SPEECH 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 deactivated (1)

by the CompactSPEECH upon each byte transfer comple-

tion It remains deactivated while the CompactSPEECH is

busy reading the byte writing the next byte or executing the

received command (after the last parameter has been re-

ceived) MWRDY is asserted by 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 (1) after the CompactSPEECH receives a GSW (Get

Status Word) command from the microcontroller After re-

set this signal is active (0) to indicate that a reset occurred

MWRQST unlike all the signals of the communication pro-

tocol is an asynchronous line that is controlled by the Com-

pactSPEECH firmware

232 Signal Use in the Interface Protocol

After reset the MWRQST signal is activated (0) and the

MWRDY signal is activated (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

mechanism 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 one

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