CM109 Datasheet, PDF (25/36 Pages) C-Media Electronics – USB I/O Controller

CM109
High Integration / Low Cost USB Audio Controller
for PC Internet Phone
report every 32mS. When there is any button pressed or released, or MCU data
coming, CM109 will transfer the 4 bytes of HID report to the USB host again.
CM109 can also transfer one byte MCU data from the USB host to its register. This is
accomplished by a ‘Set Output Report’ HID class request via default control pipe. MCU
can get this downward byte by interrupt or polling.
CM109 has one input pin ‘SCLK’ where it gets serial clock from MCU, and one
open-drain output pin ‘SDAT’ where it sends or receives serial signal to/from MCU. As
shown below, ‘SDAT’ should be stable when ‘SCLK’ is high, and can have transition only
when ‘SCLK’ is low.
START and STOP conditions shown below are the exception. Every transaction
begins from a START, and ends with a STOP, or another START (repeated START).
Date: 08/Sep/2005
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Version: 1.3a