CS49400 datasheet(68/100 Pages) CIRRUS

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Message Register.

3) Once the host knows that the DSP is ready for

a new control word, it should write the 32-bit

control word to the Host Message Register

(FA[1:0]

00b)

using

the

selected

communication mode (Intel or Motorola).

4) If the host would like to write any more 32-bit

control words to DSPC, the host should once

again poll the Host Control Register (return to

step 1).

6.3.7.2 Control Read in a Parallel Host Mode

for DSPC

When reading control data from DSPC, the same

protocol is used whether the host is reading a single

32-bit word, or a string of message words.

Reads and writes to the Host Message Register are

always 32-bits (4-bytes), and reads of the Host

Control Register are always a single byte.

The example shown in this section can be used for

any control read situation. The generic function

‘Read_Word_*()’ is used in the following example

generalized

reference

either

Read_Word_MOT() (Motorola 32-bit word read)

or Read_Word_INT() (Intel 32-bit word read).

Figure 51 shows a typical read sequence. The

protocol presented in Figure 51 will now be

described in detail.

1) Optionally, INTREQ going low may be used as

an interrupt to the host to indicate that DSPC

has an outgoing message.

2) The host reads the Host Control Register

(A[1:0] = 01b) in order to determine the state of

the communication interface.

3) In order to determine whether DSPC has an

outgoing control word that is valid, the host

must check the HOUTRDY bit of the Host

Control Register (bit 1, A[1:0] = 01b). If

HOUTRDY is high, then the Host Message

host. If HOUTRDY is low, then the DSP has

not placed a new control word in the Host

Message Register, and the host should poll the

Host Control Register again.

4) Once the host knows that the DSP is ready to

provide a new 32-bit response word, the host

can safely read a word from the Host Message

communication protocol (Motorola or Intel).

5) If the host expects to read more 32-bit response

words, the host should once again check the

FINTREQ = 0?

MORE WORDS TO

READ?

FINISHED

READ_BYTE_*( HOST

CONTROL REGISTER)

READ_WORD_*( HOST

MESSAGE REGISTER)

HOUTRDY == 1

READ_BYTE_*( HOST

CONTROL REGISTER)

HOUTRDY == 1

WAIT 100 MICROSEC

Figure 51. Typical Parallel Host Mode Control Read

Sequence Flow Diagram for DSPC

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