TLC5618, TLC5618A

PROGRAMMABLE DUAL 12-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS156E – JULY 1997 – REVISED SEPTEMBER 1999

17

POST OFFICE BOX 655303

APPLICATION INFORMATION

double-buffer-only write (D15 = low, D12 = high)

The SIR data are written to the double buffer only. Latch A and B contents are unaffected.

Serial

Interface

Register

D12 = High

D15 = Low

Latch A

Latch B

Double

Buffer

To DAC A

To DAC B

Figure 22. Double-Buffer-Only Write

purpose and use of the double buffer

Normally only one DAC output can change after a write. The double buffer allows both DAC outputs to change

after a single write. This is achieved by the two following steps.

1.

A double-buffer-only write is executed to store the new DAC B data without changing the DAC A and B

outputs.

2.

Following the previous step, a write to latch A is executed. This writes the SIR data to latch A and also

writes the double-buffer contents to latch B. Thus both DACs receive their new data at the same time,

and so both DAC outputs begin to change at the same time.

Unless a double-buffer-only write is issued, the latch B and double-buffer contents are identical. Thus, following

a write to latch A or B with another write to latch A does not change the latch B contents.

operational examples

changing the latch A data from zero to full code

Assuming that latch A starts at zero code (e.g., after power-up), the latch can be filled with 1s by writing (bit D15

on the left, D0 on the right)

1X0X 1111 1111 1111

to the serial interface. Bit D14 can be zero to select slow mode or one to select fast mode. The other X can be

zero or one (don’t care).

The latch B contents and the DAC B output are not changed by this write unless the double-buffer contents are

different from the latch B contents. This can only be true if the last write was a double-buffer-only write.

changing the latch B data from zero to full code

Assuming that latch B starts at zero code (e.g., after power-up), the latch can be filled with 1s by writing (bit D15

on the left, D0 on the right).

0X00 1111 1111 1111

to the serial interface. Bit D14 can be zero to select slow mode or one to select fast mode. The data (bits D0

to D11) are written to both the double buffer and latch B.

The latch A contents and the DAC A output are not changed by this write.