Texas Instruments TMS320C642X manual Start and Stop Conditions, Data Validity

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2.4.2Data Validity

The data on SDA must be stable during the high period of the clock (see Figure 5). The high or low state of the data line, SDA, can change only when the clock signal on SCL is low.

Figure 5. Bit Transfer on the I2C-Bus

Data line

stable data

SDA

SCL

Change of data allowed

2.5START and STOP Conditions

The I2C peripheral can generate START and STOP conditions when the peripheral is configured to be a master on the I2C-bus, as shown in Figure 6:

•The START condition is defined as a high-to-low transition on the SDA line while SCL is high. A master drives this condition to indicate the start of a data transfer.

•The STOP condition is defined as a low-to-high transition on the SDA line while SCL is high. A master drives this condition to indicate the end of a data transfer.

The I2C-bus is considered busy after a START condition and before a subsequent STOP condition. The bus busy (BB) bit of ICSTR is 1. The bus is considered free between a STOP condition and the next START condition. The BB is 0.

The master mode (MST) bit and the START condition (STT) bit in ICMDR must both be 1 for the I2C peripheral to start a data transfer with a START condition. The STOP condition (STP) bit must be set to 1 for the I2C peripheral to end a data transfer with a STOP condition. A repeated START condition generates when BB is set to 1 and STT is also set to 1. See Section 3.9 for a description of ICMDR (including the MST, STT, and STP bits).

Figure 6. I2C Peripheral START and STOP Conditions

SDA

SCL

START	STOP
condition (S)	condition (P)

12	Inter-Integrated Circuit (I2C) Peripheral	SPRUEN0D –March 2011
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