TLC320AD50C-I_15 Datasheet, PDF (29/57 Pages) Texas Instruments – SIGMA-DELTA ANALOG INTERFACE CIRCUITS WITH MASTER-SLAVE FUNCTION

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. Register programming always occurs during secondary communication. Four primary
and secondary communication cycles are required to program the four registers. If the default value for a particular
register is desired, then the register addressing can be omitted during secondary communications. The NOOP
command addresses a pseudoregister, register 0, and no register programming takes place during this secondary
communication. If secondary communication is desired for any device (either master or slave), then a secondary
communication must be requested for all devices, starting with the master. This results in a secondary frame sync
(FS) for all devices. The NOOP command can be used for devices that do not need a secondary operation.
During secondary communication, a register may be written to or read from. When writing a value to a register, DIN
contains the value to be written. When reading the value in a register, the data is stepped out on DOUT.
There are two methods for initiating secondary communications:
1. By asserting a high level on FC
2. By asserting the LSB of the DIN 16-bit serial communication high while in the15-bit mode
Both methods are illustrated in Figure 3–2.
FC
(Hardware)
(LSB of DIN)
Secondary
Request
Internal TLC320AD50C
16-Bit Mode
(Control 1 Register, Bit 0)
Figure 3–2. Hardware and Software Methods to Make a Secondary Request
FC should be pulled high before the rising edge of the frame sync (FS). This causes the start of the secondary
communication, 128 SCLKs after the start of the primary communication frame. If slaves are present, FC should
remain high until the rising edge of the frame sync for the last slave.
The second method for secondary communication is by asserting the LSB high. The least significant bit (D0) can be
used for the secondary requests as shown in Table 3–1. The request is made by placing the device in the 15-bit DAC
mode and making the LSB of DIN equal to 1. All devices should be in the 15-bit DAC mode and secondary
communication should be requested for all devices.
Table 3–1. Least Significant Bit Control Function
CONTROL BIT D0
CONTROL BIT FUNCTION
0
No operation (NOOP)
1
Secondary communication request
If a secondary communication request is made, FS goes low after 128 SCLKs after the beginning of the primary frame.
3–2