MT9V032
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14
TWO−WIRE SERIAL INTERFACE SAMPLE READ AND WRITE SEQUENCES
16−Bit Write Sequence
A typical write sequence for writing 16 bits to a register
is shown in Figure 9. A start bit given by the master, followed
by the write address, starts the sequence. The image sensor
then gives an acknowledge bit and expects the register
address to come first, followed by the 16−bit data. After each
8−bit word is sent, the image sensor gives an acknowledge
bit. All 16 bits must be written before the register is updated.
After 16 bits are transferred, the register address is
automatically incremented, so that the next 16 bits are
written to the next register. The master stops writing by
sending a start or stop bit.
Figure 9. Timing Diagram Showing a Write to R0x09 with Value 0x0284
SCLK
START ACK
0xB8 ADDR 0000 0010
R0x09
ACK ACK ACK
STOP
1000 0100
S
DATA
16−Bit Read Sequence
A typical read sequence is shown in Figure 10. First the
master has to write the register address, as in a write
sequence. Then a start bit and the read address specify that
a read is about to happen from the register. The master then
clocks out the register data 8 bits at a time. The master sends
an acknowledge bit after each 8−bit transfer. The register
address is auto−incremented after every 16 bits is
transferred. The data transfer is stopped when the master
sends a no−acknowledge bit.
Figure 10. Timing Diagram Showing a Read from R0x09; Returned Value 0x0284
SCLK
START ACK
0xB8 ADDR 0xB9 ADDR 0000 0010
R0x09
ACK ACK ACK
STOP
1000 0100
NACK
S
DATA
8−Bit Write Sequence
To be able to write 1 byte at a time to the register, a special
register address is added. The 8−bit write is done by first
writing the upper 8 bits to the desired register and then
writing the lower 8 bits to the special register address
(R0xF0). The register is not updated until all 16 bits have
been written. It is not possible to just update half of a register.
In Figure 11, a typical sequence for 8−bit writing is shown.
The second byte is written to the special register (R0xF0).
Figure 11. Timing Diagram Showing a Bytewise Write to R0x09 with Value 0x0284
STOP
ACKSTART
0xB8 ADDR
ACK
SCLK
ACKACKACKACK
R0x09
0xB8 ADDR
0000 0010 1000 0100
START
S
DATA
R0xF0
8−Bit Read Sequence
To read one byte at a time the same special register address
is used for the lower byte. The upper 8 bits are read from the
desired register. By following this with a read from the
special register (R0xF1) the lower 8 bits are accessed
(Figure 12). The master sets the no−acknowledge bits
shown.
