TLC320AD56C Datasheet, PDF (23/43 Pages) Texas Instruments – Sigma-Delta Analog Interface Circuit

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).
FC
(Hardware)
(LSB of DIN)
Secondary
Request
Internal TLC320AD56C
16-Bit Mode
(Control 1 Register,
Bit 0)
Figure 3–2. Hardware and Software Ways to Make a Secondary Request
1. 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.
2. 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
0
No operation (NOOP)
1
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.
3–3