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CLK

SYNC

ValidWriteSequence:

Output/ModeUpdates onthe24thFallingEdge

24thFallingEdge

DB23

DB0

DB23

DB0

Invalid/InterruptedWriteSequence:

Output/ModeDoesNotUpdate onthe24thFallingEdge

DAC7565

www.ti.com

SBAS412B

– FEBRUARY 2008 – REVISED MARCH 2011

SYNC INTERRUPT

LDAC FUNCTIONALITY

In a normal write sequence, the SYNC line stays low

The DAC7565 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

DAC7565 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

POWER-ON RESET TO ZERO-SCALE OR

asynchronous

DAC

updates.

LDAC

MID-SCALE

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

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

The DAC7565 contains a power-on reset circuit that

Multiple single-channel updates can be done in order

controls

the

output

voltage

during

power-up.

to set different channel buffers to desired values and

Depending on the RSTSEL signal, on power-up, the

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

DAC registers are reset and the output voltages are

channels must be loaded with desired data before an

set to zero-scale (RSTSEL = 0) or mid-scale

LDAC

rising

edge.

After

low-to-high

LDAC

(RSTSEL = 1); they remain that way until a valid write

transition, all DACs are simultaneously updated with

sequence and load command are made to the

the contents of the corresponding data buffers. If the

respective DAC channel. The power-on reset is

contents of a data buffer are not changed by the

useful in applications where it is important to know

serial

interface,

the

corresponding

DAC

output

the state of the output of each DAC while the device

remains unchanged after the LDAC trigger.

is in the process of powering up.

No device pin should be brought high before power is

ENABLE PIN

applied to the device. The internal reference is

powered on by default and remains that way until a

For normal operation, the enable pin must be driven

valid reference-change command is executed.

to a logic low. If the enable pin is driven high, the

DAC7565 stops listening to the serial port. However,

SCLK, SYNC, and DIN must not be kept floating, but

must be at some logic level. This feature can be

useful for applications that share the same serial port.

Figure 95. SYNC Interrupt Facility

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