CM109 Datasheet, PDF (28/36 Pages) C-Media Electronics – USB I/O Controller

CM109
High Integration / Low Cost USB Audio Controller
for PC Internet Phone
The figure below shows typical transactions between MCU and CM109. After a
START, MCU should send 7-bit slave address (0111000) first, and then the 8th bit
denotes a read transfer when it’s high; or a write transfer when it’s low.
MCU write:
S 0x70 0
0x00 0
Byte 0 0
Byte 1 0
Byte 2 0
Byte 3 0 P
MCU read:
S 0x70 0 0x04 0
S 0x71 0 Byte 0 0 Byte 1 0 Byte 2 0 Byte 3 1 P
S
0
Byte n
From CM109 to MCU
START condition
Positive acknowledge
One byte data (address n)
From MCU to CM109
P
STOP condition
1
Negative acknowledge
In a write transfer, MCU keeps acting as the transmitter. CM109 regards the first
DATA byte as start register address (it’s better to be 0x00). The following four DATA
bytes are the content that MCU writes to the register addresses. In a read transfer,
two transactions are necessary. MCU resets start register address by the first
transaction. Then MCU changes to be the receiver during the second transaction to
get four bytes of data.
Note 1: Bits 0~3 of the first HID byte always reflect button activity, so they can not be
written by MCU.
Date: 08/Sep/2005
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Version: 1.3a