AMC7812SPAPR Datasheet, PDF (58/92 Pages) Texas Instruments – 12-Bit Analog Monitoring and Control Solution with Multichannel ADC, DACs, and Temperature Sensors

AMC7812
SBAS513E – JANUARY 2011 – REVISED SEPTEMBER 2013
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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.
C
B
A
SDI
SDI-C SDO-C
SDI-B
SDO-B
SDI-A
SDO-A
SDO
CS
SCLK
Figure 108. Three AMC7812s in a Daisy-Chain Configuration
CS
SDI-C
SDO-C
SDI-B
SDO-B
SDI-A
SDO-A
Cycle 0
RA0 RB0 RC0
XX RA0 RB0
XX RA0 RB0
XX
XX RA0
XX
XX RA0
XX
XX
XX
Cycle 1
RA1
CD0
CD0
BD0
BD0
AD0
RB1
RA1
RA1
CD0
CD0
BD0
RC1
RB1
RB1
RA1
RA1
CD0
Cycle 2
RA2
CD1
CD1
BD1
BD1
AD1
RB2
RA2
RA2
CD1
CD1
BD1
RC2
RB2
RB2
RA2
RA2
CD1
RAn (RBn, RCn) = Read Command for Register N of device A (B,C)
ADn (BDn, CDn) = Data from Register N of device A (B, C)
XX = Don’t care, undefined
Figure 109. Reading Multiple Registers
Cycle 3
RA3
CD2
CD2
BD2
BD2
AD2
RB3
RA3
RA3
CD2
CD2
BD2
RC3
RB3
RB3
RA3
RA3
CD2
58
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