AD7457: Discontinuous clock

Document created by analog-archivist Employee on Feb 23, 2016
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We need to connect the AD7457 to the SPI bus of the MPC8347E. The idea was to
use a general purpose IO to control the CS\ of the AD7457, then read out the
result of the conversion.

We have 2 questions about this.

1: can the AD7457 work with a gapped clock? We would start the conversion by
triggering the CS\ pin. At that moment there would be no SCLK. The SCLK would
only become active during readout. The SPI SCLK clock of the MPC8274E is only
active during transactions on the SPI bus.

2: can we connect two AD7457 to the same SPI bus, with separate CS\? In this
case, they would sometimes see SCLK activity when the other AD7457 on the bus
is accessed.


1) The AD7457 will work fine with a discontinuous clock.

2) There should be no implications on the deselected device due to clock
activity since the deselected device won't be converting at the time.  The
SDATA output of the deselected device will always be tri-stated.