CS494002 datasheet(56/100 Pages) CIRRUS

56 / 100 page

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()

(Motorola

byte

read)

Read_Byte_INT() (Intel byte read). Figure 41

shows a typical read sequence. The protocol

presented in Figure 41 will now be described in

detail.

1) Optionally, FINTREQ going low may be used

as an interrupt to the host to indicate that

DSPAB has an outgoing message. Note that

even with the use of FINTREQ, HOUTRDY

must be checked to ensure that the current byte

is readytobereadbythe hostduringthe read

process. Please note that the state of FINTREQ

is undefined during boot, and it is valid only

once the application code is loaded.

2) The host reads the Host Control Register

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

of the communication interface.

3) In order to determine whether DSPAB has an

outgoing control byte that is valid, the host

must check the HOUTRDY bit of the Host

Control Register (bit 1, FA[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 byte 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 response byte, the host can

safely read a byte from the Host Message

communication protocol (Motorola or Intel).

5) If the host expects to read any more response

bytes, the host should once again check the

HOUTRDY bit (return to step 1). Messages

from the application code (post-download) on

the DSP will always be 6 bytes, unless

otherwise stated in the associated Application

Note.

6) After the response has been read the host

should wait at least 100 uS and check

HOUTRDY one final time. If HOUTRDY is

high once again this means that an unsolicited

message has come during the read process and

the host has another message to read (i.e. skip

back to step 4 and read out the new message). It

is the host’s responsibility to insure that any

pending messages are read from the DSP.

F I NT RE Q = 0 ?

( o p t ional)

M O R E BYT ES T O

RE A D ?

F I N ISH ED

R E AD _ B YT E _ * ( H O S T

CO NT RO L R E G I S T E R)

R E AD _ B YT E _ * ( H O S T

M E SS AG E R EG I S T E R )

HO U T RD Y = = 1

R E AD _ B YT E _ * ( H O S T

CO NT RO L R E G I S T E R)

HO U T RD Y = = 1

W A I T 100 M IC R O S E C

Figure 41. Typical Parallel Host Mode Control Read

Sequence Flow Diagram for DSPAB

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