Datasheet

DB23 DB0
=Don’tCare
Bit23=MSB
Bit0=LSB
MultipleReadings
CS
SCLK
SDI
CommandtoRead
RegisterA
CommandtoRead
RegisterB
DB23 DB0 DB23 DB0 DB23 DB0
CommandtoRead
RegisterC
NOPCommand
(write ‘1’ toNOPbit)
DB23 DB0
SDO
Undefined Datafrom
RegisterA
DB23 DB0 DB23 DB0 DB23 DB0
Datafrom
RegisterB
Datafrom
RegisterC
DB23DB0
SingleReading
CS
SCLK
SDI
READCommandSpecifies
RegistertobeRead
NOPCommand
(write ‘1’ toNOPbit)
DB23
DB23DB0
SDO
Undefined Datafrom
SelectedRegister
DB23
R/W= ‘1’ R/W= ‘0’
R/W= ‘1’ R/W= ‘1’ R/W= ‘1’ R/W= ‘0’
DB23
Command
DB23
Undefined
DB0
DB0
DB0
DB0
DAC8218
SBAS460A –MAY 2009–REVISED DECEMBER 2009 www.ti.com
Shift Register, thus greatly speeding up the data transfer. For example, consider three DAC8218s (A, B, and C)
in a daisy-chain configuration. The data from the SPI controller are transferred first to A, then to B, and finally to
C. In normal daisy-chain operation, a total of 72 clocks are needed to transfer one word to C. However, if A and
B are placed into Sleep mode, the first 24 data bits are directly transferred to C (through A and B); therefore, only
24 clocks are needed.
To wake the device up from sleep mode and return to normal operation, either one of following methods can be
used:
1. Pull the WAKEUP pin low, which forces the SLEEP bit to '0' and returns the device to normal operating
mode.
2. Use the W2 bit and the CS pin.
When the W2 bit = '1', if CS is applied with no more than one falling edge of SCLK, then the rising edge of CS
wakes the device from sleep mode back to normal operation. However, the device will not wake-up if more than
one falling edge of SCLK exists while CS is low.
Read-Back Operation
The READ command is used to start read-back operation. However, before read-back operation can be initiated,
the SDO pin must be enabled by setting the DSDO bit in the Configuration Register to '0'; this bit is cleared by
default. Read-back operation is then started by executing a READ command (R/W bit = '1', see Table 9). Bits A4
to A0 in the READ command select the register to be read. The remaining data in the command are don’t care
bits. During the next SPI operation, the data appearing on the SDO output are from the previously addressed
register. For a read of a single register, a NOP command can be used to clock out the data from the selected
register on SDO. Multiple registers can be read if multiple READ commands are issued. The readback diagram
in Figure 100 shows the read-back sequence.
Figure 100. Read-Back Operation
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