Datasheet

2.5 Register Loop-Back Jumper
The evaluation module contains a loop-back jumper, labeled SDO_R. The purpose of this jumper is
to allow read back of the gain register values. This is helpful when diagnosing problems with the PC
parallel port interface or host controller communications.
The serial interface is basically a 32 bit serial IN, serial OUT shift register. The SDI pin is the input,
while SDO is the output. As 32 bits of new data are shifted into the PGA4311, the previously
programmed 32-bits are being shifted out. This allows the user to read back the values to determine
if the device is being programmed correctly. It also allows multiple PGA4311 devices to be cascaded,
or daisy-chained, to form a 32 • N-bit long shift register, where N is the number of devices included
in the chain. This arrangement allows a 3-wire interface to program multiple PGA4311 devices
connected in a daisy-chain fashion.
Hardware Guide
2-3