There are several other considerations
for writing on the SPI:
- The R/W bit must be set to 0.
- The data on SDI pin is
clocked into a shift register on each rising edge on the SCK pin.
- The CS# must be held low for
data to be clocked. The device ignores clock pulses if CS# is held
high.
- Recommended SPI settings for
this device are CPOL=0 and CPHA=0.
- When SCK and SDI lines are
shared between devices, TI recommends to hold the CS# line high on the
device that is not to be clocked.
There are several other considerations
for SPI readback:
- The R/W bit must be set to 1.
- The MUXOUT pin remains
tri-stated for the address portion of the transaction.
- The data on MUXOUT is clocked
out at the falling edge of SCK. In other words, the readback data is
available at the MUXOUT pin tCD after the clock falling
edge.
- The data portion of the
transition on the SDI line is always ignored.
- The MUXOUT pin is
automatically enabled during the readback transaction. After readback
activity is over, it is automatically tri-stated. MUXOUT pin has dual
functionality in multiplier mode, as multiplier lock status is also
indicated on MUXOUT pin. When sharing the SPI bus readback pin with other
devices, make sure to set LD_DIS=1, if readback is required in multiplier
mode.
- If READBACK_CTRL is set to 0,
the values read back even for R/W bits are not always the value written but
rather an internal device state that takes into account the programmed value
as well as other factors, such as pin states.