Cirrus Logic CS8420 - Manual (Page 54)

54 DS245F4
CS8420
Miscellaneous Pins:
U - User Data
The U pin may optionally be used to input User data for transmission by the AES3 transmitter (see Figure 20 for
timing information). Alternatively, the U pin may be set to output User data from the AES3 receiver (see Figure 19
for timing information). If not driven, a 47 k Ω pull-down resistor is recommended for the U pin since the default state
of the UD direction bit sets the U pin as an input. The pull-down resistor ensures that the transmitted user data will
be zero. If the U pin is always set to be an output, thereby causing the U bit manager to be the source of the U data,
the resistor is not necessary. The U pin should not be tied directly to ground in case it is programmed to be an output
and subsequently tries to output a logic high. This situation may affect the long-term reliability of the device. If the U
pin is driven by a logic level output, a 100
Ω series resistor is recommended.