CS493253 datasheet(49/90 Pages) CIRRUS

49 / 90 page

CS49300 Family DSP

DS339F7

either Read_Byte_MOT() or Read_Byte_INT(),

and ‘Write_Byte_*()’ is a generic reference to

Write_Byte_MOT() or Write_Byte_INT(). Figure 28

shows a typical write sequence. The protocol

presented in Figure 28 will now be described in

detail.

1) When the host is communicating with the

CS493XX, the host must verify that the DSP is

ready to accept a new control byte. If the DSP

is in the midst of an interrupt service routine, it

will be unable to retrieve control data from the

Host Message Register. Please note that

‘Read_Byte_*()’

and

‘Write_Byte_*()’

are

generic references to either the Intel or

Motorola communication protocol.

If the most recent control byte has not yet

been read by the DSP, the host must not

write a new byte.

2) In order to determine whether the CS493XX is

ready to accept a new control byte the host

must check the HINBSY bit of the Host Control

DSP is not prepared to accept a new control

byte, and the host should poll the Host Control

may write a control byte into the Host Message

3) The host knows that the DSP is ready for a new

control byte at this point and should write the

control byte to the Host Message Register

(A[1:0] = 00b).

4) If the host would like to write any more control

bytes to the CS493XX, the host should once

again poll the Host Control Register (return to

step 1).

6.2.3.2. Control Read in a Parallel Host

Mode

When reading control data from the CS493XX, the

same protocol is used whether the host is reading

a single byte or a 6 byte message.

During the boot procedure, a handshaking protocol

is used by the CS493XX. This handshake consists

of a 3 byte write to the CS493XX followed by a 1

byte response from the DSP. The host must read

the response byte and act accordingly. The boot

procedure is discussed in Section 8.1, “Host Boot”

on page 54.

During

regular

operation

(at

run-time),

the

responses from the CS493XX will always be 6

bytes in length.

The example shown in this section can be used for

any control read situation. The generic function

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

generalized

reference

either

Read_Byte_MOT()

Read_Byte_INT().

Figure 29 shows a typical read sequence. The

protocol presented in Figure 29 will now be

described in detail.

1) Optionally, INTREQ going low may be used as

an interrupt to the host to indicate that the

CS493XX has an outgoing message. Even

with the use of INTREQ, HOUTRDY must be

checked to insure that bytes are ready for the

host during the read process. Please note that

INTREQ does not go low to indicate an

outgoing message during boot.

2) The host reads the Host Control Register

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

Figure 28. Typical Parallel Host Mode Control

Write Sequence Flow Diagram

READ_BYTE_*(HOST CONTROL REGISTER)

WRITE_BYTE_*(HOST MESSAGE REGISTER)

MORE BYTES

HINSBY==1

YES

TO WRITE?

YES

FINISHED

CS493253 Datasheet(PDF) 49 Page - Cirrus Logic

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