DAC8564IAPW datasheet(29/46 Pages) TI

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SYNC INTERRUPT

LDAC FUNCTIONALITY

POWER-ON RESET TO ZERO-SCALE

CLK

SYNC

ValidWriteSequence:

Output/ModeUpdates onthe24thFallingEdge

24thFallingEdge

DB23

DB0

DB23

DB0

Invalid/InterruptedWriteSequence:

Output/ModeDoesNotUpdate onthe24thFallingEdge

DAC8564

SBAS403A – JUNE 2007 – REVISED NOVEMBER 2007

In a normal write sequence, the SYNC line stays low

The DAC8564 offers both a software and hardware

for at least 24 falling edges of SCLK and the

simultaneous

update

function.

The

DAC

addressed DAC register updates on the 24th falling

double-buffered architecture has been designed so

edge. However, if SYNC is brought high before the

that new data can be entered for each DAC without

24th falling edge, it acts as an interrupt to the write

disturbing the analog outputs.

sequence; the shift register resets and the write

DAC8564 data updates are synchronized with the

sequence is discarded. Neither an update of the data

falling edge of the 24th SCLK cycle, which follows a

buffer contents, DAC register contents, nor a change

falling edge of SYNC. For such synchronous updates,

the

operating

mode

occurs

(as

shown

the LDAC pin is not required and it must be

Figure 95).

connected to GND permanently. The LDAC pin is

used as a positive edge triggered timing signal for

asynchronous

DAC

updates.

LDAC

operation, single-channel store(s) should be done

The DAC8564 contains a power-on reset circuit that

(loading DAC buffers) by setting LD0 and LD1 to '0'.

controls the output voltage during power-up. On

Multiple single-channel updates can be done in order

power-up, the DAC registers are filled with zeros and

to set different channel buffers to desired values and

the output voltages are set to zero-scale; they remain

then make a rising edge on LDAC. Data buffers of all

that way until a valid write sequence and load

channels must be loaded with desired data before an

command are made to the respective DAC channel.

LDAC

rising

edge.

After

low-to-high

LDAC

The power-on reset is useful in applications where it

transition, all DACs are simultaneously updated with

is important to know the state of the output of each

the contents of the corresponding data buffers. If the

DAC while the device is in the process of powering

contents of a data buffer are not changed by the

up. No device pin should be brought high before

serial

interface,

the

corresponding

DAC

output

power is applied to the device. The internal reference

remains unchanged after the LDAC trigger.

is powered on by default and remains that way until a

valid reference-change command is executed.

Figure 95. SYNC Interrupt Facility

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