CM109 Datasheet, PDF (27/36 Pages) C-Media Electronics – USB I/O Controller

CM109
High Integration / Low Cost USB Audio Controller
for PC Internet Phone
In the write transfer, MCU keep acting as the master and the transfer direction is not
changed. The following figure gives an example of one byte write transfer.
CM109 regards the first DATA byte as the register address. The second DATA byte is
the content that MCU writes at the register address. If there is the third DATA byte,
CM109 will auto-increment this byte to the next register address.
The figure below shows an example of two bytes read transfer. Because CM109 has
auto-increment function, the second DATA byte will be the register data on the next
address.
Please note that the USB host tries to get new HID data every 32mS. It’s quite slow.
If the continuous write transfers are too close in time, the former transfer may have no
effect.
Date: 08/Sep/2005
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Version: 1.3a