CS493105 View Datasheet(PDF) - Cirrus Logic
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MFG CO.
CS493105 Datasheet PDF : 90 Pages
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CS49300 Family DSP
SPI START: CS (LOW)
WRITE ADDRESS BYTE
WITH MODE BIT
SET TO 0 FOR WRITE
NO
INTREQ LOW?
YES
SEND DATABYTE
Y
MORE DATA?
N
CS (HIGH)
CS (LOW)
WRITE ADDRESS BYTE
WITH MODE BIT
SET TO 1 FOR READ
READ DATA BYTE
Figure 19. SPI Write Flow Diagram
4) When all of the bytes have been transferred,
chip select should be raised to signify an end of
write. Once again it is crucial that the serial
clock transitions from high to low on the last bit
of the last byte before chip select is raised, or a
loss of data will occur.
The same write routine could be used to send a
single byte, message or an entire application code
image. From a hardware perspective, it makes no
difference whether communication is by byte or
multiple bytes of any length as long as the correct
hardware protocol is followed.
6.1.1.2. Reading in SPI
A read operation is necessary when the CS493XX
signals that it has data to be read. The CS493XX
does this by dropping its interrupt request line
(INTREQ) low. When reading from the device in
SPI, the same protocol will be used whether
reading a single byte or multiple bytes. The
examples shown in this document can be
expanded to fit any read situation. Figure 20, "SPI
Read Flow Diagram" on page 37 shows a typical
read sequence:
YES
INTREQ STILL LOW?
NO
CS (HIGH)
Figure 20. SPI Read Flow Diagram
The following is a detailed description of an SPI
read sequence with the CS493XX.
1) An SPI read transaction is initiated by the
CS493XX dropping INTREQ, signaling that it
has data to be read.
2) The host responds by driving chip select (CS)
low.
3) This is followed by a 7-bit address and the
read/write bit set high for a read. The address
for the CS493XX defaults to 0000000b. It is
necessary to clock this address in prior to any
transfer in order for the CS493XX to
acknowledge the read. In other words a byte of
0x01 should be clocked into the device
preceding any read. The 0x01 byte represents
the 7 bit address 0000000b, and the least
DS339F7
37
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