TLC320AD55CDW datasheet(23/41 Pages) TI1

23 / 41 page

3–5

In Figure 3–6, FC hardware terminal 15 is left in its nonasserted state (0). FC is asserted through software

by embedding an asserted high level (1) in the LSB of the 16-bit primary word. This is possible when not

in 16-bit mode (control 1 register bit 2 = 0) because the user is using only 15 bits of DAC information.

ADC Data

Out

ADC Data

Out

DAC Data In

DOUT

DAC Data In

DIN

ADC Data

Out

All Bits 0

16 SCLKs

Communication Frame 1 (CF1)

NOTE A: For a read cycle, the last 8 bits are don’t care.

D15–D1

D0 = 0

D15–D1

D0 = 1

(Secondary

Read)

(Secondary

Read or Write)

(Secondary

Write)

Primary

Secondary

Primary

No Secondary

Request

64 FCLKs†

32 FCLKs†

Data

Secondary

Update

† See Fk divide register in Appendix A.

Communication Frame 2 (CF2)

ADC Data

Out

8 SCLKs

Software FC Bit

Figure 3– 6. Software FC Secondary Request (Phone Mode Disabled)

Table 3–2 shows the secondary communications format. D13 is the R/W bit, the read/not-write bit.

D12 through D8 are address bits. The register map is specified in the register set section in Appendix A.

D7 through D0 are data bits. The data bits are values for the specified register addressed by data bits D12

through D8.

Table 3– 2. Secondary Communication Data Format

D15

D14

D13

D12

D11

D10

R/W

3.3

Conversion Rate Versus Serial Port

The SCLK frequency can be programmed independently from the FCLK frequency. This can create a

problem with the interpretation of the serial port data. The serial port is designed to initiate a primary

communication every 64 SCLKs. There must be an integer number of SCLKs

≥ 40 per sample period. Two

examples follow to demonstrate the possible output of the serial port. SCLK must be fast enough to collect

all data from each frame.

Example 1: MCLK = 4.096 MHz, sample rate = 8 kHz, 8 kHz = MCLK/ (Fk

× 256), set Fk = 2,

SCLK = MCLK/ (Fsclk

× 2), set Fsclk = 2, SCLK = 1.024 MHz. With this configuration,

SCLK = sample rate

× 128. Therefore, each primary communication is a valid sample.

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