The DACx0501 digital interface is programmed to work in I²C mode when the logic level of the SPI2C pin is 1 at power up. In I²C mode, the DACx0501 have a 2-wire serial interface: SCL, SDA, and one address pin, A0, as shown in Section 6. The I²C bus consists of a data line (SDA) and a clock line (SCL) with pull-up structures. When the bus is idle, both the SDA and SCL lines are pulled high. All the I²C-compatible devices connect to the I²C bus through the open-drain I/O pins, SDA and SCL.

The I²C specification states that the device that controls communication is called a controller, and the devices that are controlled by the controller are called targets. The controller device generates the SCL signal. The controller device also generates special timing conditions (start condition, repeated start condition, and stop condition) on the bus to indicate the start or stop of a data transfer. Device addressing is completed by the controller. The controller device on an I²C bus is typically a microcontroller or DSP. The DACx0501 operate as a target device on the I²C bus. A target device acknowledges controller commands, and upon controller control, receives or transmits data.

Typically, the DACx0501 operate as a target receiver. A controller device writes to the DACx0501, a target receiver. However, if a controller device requires the DACx0501 internal register data, the DACx0501 operate as a target transmitter. In this case, the controller device reads from the DACx0501 According to I²C terminology, read and write refer to the controller device.

The DACx0501 are target devices that support the following data transfer modes:

1. Standard mode (100Kbps)
2. Fast mode (400Kbps)
3. Fast mode plus (1.0Mbps)

The data transfer protocol for standard and fast modes is exactly the same; therefore, these modes are referred to as F/S-mode in this document. The fast-mode plus (FM+) protocol is supported in terms of data transfer speed, but not output current. The low-level output current is 3 mA, similar to the case of standard and fast modes. The DACx0501 support 7-bit addressing. The 10-bit addressing mode is not supported. These devices support the general call reset function. Send the following sequence to initiate a software reset within the device: Start/Repeated Start, 0x00, 0x06, Stop. The reset is asserted within the device on the falling edge of the ACK bit, following the second byte.

Other than specific timing signals, the I²C interface works with serial bytes. At the end of each byte, a ninth clock cycle generates and detects an acknowledge signal. Acknowledge is when the SDA line is pulled low during the high period of the ninth clock cycle. A not-acknowledge is when the SDA line is left high during the high period of the ninth clock cycle as shown in Figure 8-4.

Figure 8-4 Acknowledge and Not Acknowledge on the I²C Bus