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4.4
The link layer protocol
The general protocol format is:
MD header
·
all multi-drop (MD) headers have the top bit set
·
the device address is a single byte in the range 0 to 16
·
all undefined commands have no effect
Multi-drop headers
The following MD headers may be transmitted to the 4407 by a controller
F3 - Send device data
This is followed by a device address and any command message for the 4407.
F4 - Device data request
This is followed by a device address. The device must respond with a single byte of
data. The null response may be sent if no data is ready.
F5 - Group poll
This causes any device with data to transmit a single null character. If more than one
device replies the controller may receive an overrun, framing or parity error. The
controller interprets any character received or any of the above error conditions as a
request to send data by one of the devices.
The multi-drop link layer only packages outgoing messages as all incoming data is of
one byte length.
4.5
Message layer
After the controller has issued a send device data byte (F3) followed by a device
address (hex 0l-l0), the next byte sent will be a command to that device.
The controller can send the following commands to the 4407:
set output level gain
This command sets the audio input, output gain, HHHH are the high gain bits, while
LLLL are the lower gain bits. Step size is 0.09375 dB per bit.
HHHHLLLL = 00 = -12db minimum gain setting
HHHHLLLL = 80 = 0db unity gain (if greater than 80 gain is set to 0db)
16
Device address
- byte 1 : 0001HHHH
- byte 2 : 0000LLLL
4407
Message
Issue 2
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