Datasheet

RA0 RB0
RC0
RA0 RB0
RA0
RB0
RA0
RA0
RA1 RB1 RC1
RA1 RB1
CD0
BD0
CD0
RA1 RB1
CD0 RA1
AD0
BD0 CD0 RA1
BD0 CD0
RA2 RB2
RC2
CD1 RA2 RB2
CD1
RA2 RB2
BD1 CD1 RA2
BD1 CD1 RA2
AD1 BD1 CD1
RA3
RB3 RC3
CD2
RA3 RB3
CD2
RA3 RB3
BD2
BD2
CD2 RA3
CD2 RA3
AD2 BD2
CD2
XX
XX
XX
XX
XX
XX
XX
XX
XX
CS
SDI-C
SDO-C
SDI-B
SDO-B
SDI-A
SDO-A
Cycle0 Cycle1 Cycle2
Cycle3
RA
XX=Don’tcare,undefined
n n n N
n n n N
(RB ,RC )=ReadCommandforRegister ofdeviceA(B,C)
AD (BD ,CD )=DatafromRegister ofdeviceA(B,C)
SDI-C SDO-C
C
SDI-B SDI-A
SDO-B SDO-A
B A
SDO
SDI
CS
SCLK
AMC7812
SBAS513E –JANUARY 2011–REVISED SEPTEMBER 2013 www.ti.com
Daisy-Chain Operation
For systems that contain several AMC7812s, the SDO pin can be used to daisy-chain multiple devices together.
This daisy-chain feature is useful in reducing the number of serial interface lines. The first falling edge of CS
starts the operation cycle. SCLK is continuously applied to the Input Shift Register when CS is low.
If more than 24 clock pulses are applied, the data ripple out of the Shift Register and appear on the SDO line.
These data are clocked out on the rising edge of SCLK and are valid on the falling edge. By connecting the SDO
output of the first device to the SDI input of the next device in the chain, a multiple-device interface is
constructed. Each device in the system requires 24 clock pulses. Therefore, the total number of clock cycles
must equal 24N, where N is the total number of AMC7812s in the daisy chain. When the serial transfer to all
devices is complete, CS is taken high. This action transfers the data from the SPI Shifter Registers to the internal
register of each AMC7812 in the daisy chain and prevents any further data from being clocked in. The serial
clock can be continuous or gated. A continuous SCLK source can only be used if CS is held low for the correct
number of clock cycles. In gated clock mode, a burst clock containing the exact number of clock cycles must be
used and CS must be taken high after the final clock in order to latch the data.
Figure 108. Three AMC7812s in a Daisy-Chain Configuration
Figure 109. Reading Multiple Registers
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