TLC320AD55CDW datasheet(21/41 Pages) TI1

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3–3

3.2

Secondary Serial Communication

Secondary serial communication reads or writes 16-bit words that program both the options and the circuit

configurations of the device. All register programming occurs during secondary communications. Four

primary and secondary communication cycles are required to program the four registers. When the default

value for a particular register is desired, the user can omit addressing it during secondary communication.

A no-op command addresses the no-op register (register 0), and no register programming takes place

during this secondary communication.

There are two methods for initiating secondary communications (see Figure 3–3):

1) by asserting a high level on FC, or 2) by asserting the LSB of DIN 16-bit serial communication high while

not in 16-bit mode (see control 1 register bit 0).

Secondary

Request

16-Bit Mode

(Control 1 Register,

Bit 0)

(Hardware)

(LSB 0f DIN)

Internal TLC320AD55C

Figure 3– 3. Hardware and Software Methods to Initate a Secondary Request

Figures 3–5 and 3–6 show the two different methods by which FC requests secondary

communication words as well as the timing for FS, DOUT, DIN, and SCLK. The examples span

two primary communication frames. Figure 3–5 shows the use of hardware function control.

During a secondary communication, a register can be written to or read from. When writing a

value to a register, DIN contains the value to be written (see Figure 3–7). The data returned on

DOUT is 00(hex). When performing a read function, DIN can still provide data to be written to an

addressed register; however, DOUT contains the most recent value contained in the register

addressed by DIN.

DIN

(Secondary

Read)

8 Bits

DIN

(Secondary

Write)

8 Bits

R/W

Don’t Care

Data to the

Figure 3– 4. Secondary DIN Format

In Figure 3–5, FC clocks in and latches on the rising edge of frame sync (FS). This causes the

start of the secondary update 32 FCLKs (see Fk divide register, Appendix A) after the start of the

primary communication frame. Read and write examples are shown for DIN and DOUT.

Figure 3–6 shows the use of software function control.

The software request for function control is typically used when the required resolution of the DAC

channel is less than 16 bits. Then the least significant bit (D0) can be used for the secondary

requests as shown in Table 3–1.

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