TLC320AD56 datasheet(23/42 Pages) TI1

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3–3

3.2

Secondary Serial Communication

Secondary serial communication is used to read or write 16-bit words that program both the options and the

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

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

value for a particular register is desired, then the user could omit addressing it during secondary

communication. The NOOP command addresses a pseudo-register, register 0, and no register

programming takes place during this secondary communication.

There are two methods for initiating secondary communications. They are 1) by asserting a high signal level

on FC, or 2) by asserting the LSB of the 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 of DIN)

Internal TLC320AD56C

Figure 3–2. Hardware and Software Ways to Make a Secondary Request

Figures 3–3 and 3–4 show the two different ways FC requests secondary communication words

as well as the timing for FS, DOUT, DIN, and SCLK. The examples span two primary

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

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

value to a register, the DIN line contains the value to be written. The data returned on DOUT is

00H. When performing a read function, the DIN line may still provide data to be written to an

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

addressed by DIN.

In Figure 3–3, FC is clocked in and latched on the rising edge of frame sync (FS). This causes

the start of the secondary information 32 FCLKs after the start of the primary communication

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

Figure 3–4 shows the use of software function control.

The software request 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 3–2.

Table 3–2. Least Significant Bit Control Function

Control Bit D0

Control Bit Function

No operation (NOOP)

Secondary communication request

On the falling edge of the next FS, D15–D1 is input to DIN or D15–D0 is output to DOUT.

When a secondary communication request is made, FS goes low 32 FCLKs after the beginning of the

primary frame.

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