TLC320AD50CSLASHI datasheet(29/54 Pages) TI2

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3–2

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

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:

By asserting a high level on FC

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.

Secondary

Request

16-Bit Mode

(Control 1 Register, Bit 0)

(Hardware)

(LSB of DIN)

Internal TLC320AD50C

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

No operation (NOOP)

Secondary communication request

If a secondary communication request is made, FS goes low after 128 SCLKs after the beginning of the primary frame.

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