SPRZ545C July 2023 – March 2024 TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1
I2C: Target Transmitter Mode, Standard Mode SDA Timings Limitation
0, A
The I2C peripheral present on the MCU is a Fast-mode device; it will clock-stretch the SCL (Clock) line when used with a Standard-mode host.
There is a requirement from the I2C Specification for a Fast-mode device used in a Standard-mode system to meet tSU:DAT (data set-up time) + tr(max) (rise time) before releasing the SCL line. See Footnote 4 of the "Characteristics of the SDA and SCL bus lines for Standard, Fast, and Fast-mode Plus I2C-bus devices" table in the NXP Semiconductors I2C-bus specification and user manual (UM10204).
However, the C2000 I2C clock-stretches the SCL line by a fixed amount = 6 * fmod Clock (I2C Clock rate of the C2000) in the above scenario. When the C2000™ microcontroller is acting as a target transmitter with a Standard-mode host, it is possible for the clock line (SCL) to be released by the C2000 before the data (SDA) is ready, if the tr of SDA is too long.
The "Pull-up resistor sizing" section in the NXP Semiconductors I2C-bus specification and user manual (UM10204) gives more details on choosing the appropriate PU resistor(Rp ), based on the rise time (tr ) and bus capacitance (Cb ) shown in Equation 1.
fmod Clock (MHz) | fmod Period (ns) | SCL Clock- Stretch Delay from C2000 I2C (ns): (6*fmod Clock) | Data Set-up Time (ns): tSU:DAT (Standard Mode) | SDA Data Rise Time Requirement (ns): tr |
---|---|---|---|---|
7 | 142.9 | 857 | 250 | 607 |
8 | 125 | 750 | 500 | |
9 | 111 | 666 | 416 | |
10 | 100 | 600 | 350 | |
11 | 90.9 | 545 | 295 | |
12 | 83.3 | 500 | 250 |
fmod Clock (MHz) | SDA Data Rise Time Requirement (ns): tr | Rp (kΩ) for Cb = 100 pF |
Rp (kΩ) for Cb = 200 pF |
Rp (kΩ) for Cb = 300 pF |
Rp (kΩ) for Cb = 400 pF |
---|---|---|---|---|---|
7 | 607 | 7.1 | 3.5 | 2.3 | 1.7 |
8 | 500 | 5.9 | 2.9 | 1.9 | 1.4 |
9 | 416 | 4.9 | 2.4 | 1.6 | 1.2 |
10 | 350 | 4.1 | 2.0 | 1.3 | 1.0 |
11 | 295 | 3.4 | 1.7 | 1.1 | 0.8 |
12 | 250 | 2.9 | 1.4 | 0.9 | 0.7 |