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Functional Description
1321
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Inter-Integrated Circuit (I
2
C) Interface
19.3.2.1 Standard, Fast, and Fast Plus Modes
Standard, fast, and fast plus modes are selected using a value in the I
2
C Master Timer Period (I2CMTPR)
register that results in an SCL frequency of 100 kbps for standard mode, 400 kbps for fast mode, or 1
Mbps for fast mode plus.
The I
2
C clock rate is determined by the parameters CLK_PRD, TIMER_PRD, SCL_LP, and SCL_HP
where:
•
CLK_PRD is the system clock period
•
SCL_LP is the low phase of SCL (fixed at 6)
•
SCL_HP is the high phase of SCL (fixed at 4)
TIMER_PRD is the programmed value in the I2CMTPR register (see
). This value is
determined by replacing the known variables in
and solving for TIMER_PRD. The I
2
C clock
period is calculated as follows:
SCL_PERIOD = 2 × (1 + TIMER_PRD) × ( SCL_HP) × CLK_PRD
(61)
For example:
•
CLK_PRD = 50 ns
•
TIMER_PRD = 2
•
SCL_LP = 6
•
SCL_HP = 4
Yields an SCL frequency of: 1 / SCL_PERIOD = 338 KHz
lists examples of the timer periods that should be used to generate standard, fast mode, and
fast mode plus SCL frequencies based on various system clock frequencies.
Table 19-1. Examples of I
2
C Master Timer Period Versus Speed Mode
System Clock
Standard Mode
Fast Mode
Fast Mode Plus
Timer Period
Data Rate
Timer Period
Data Rate
Timer Period
Data Rate
4 MHz
0x01
100 kbps
-–
–
–
–
6 MHz
0x02
100 kbps
–
–
–
–
12.5 MHz
0x06
89 kbps
0x01
312 kbps
–
–
16.7 MHz
0x08
93 kbps
0x02
278 kbps
–
–
20 MHz
0x09
100 kbps
0x02
333 kbps
–
–
25 MHz
0x0C
96.2 kbps
0x03
312 kbps
–
–
33 MHz
0x10
97.1 kbps
0x04
330 kbps
–
–
40 MHz
0x13
100 kbps
0x04
400 kbps
0x01
1000 kbps
50 MHz
0x18
100 kbps
0x06
357 kbps
0x02
833 kbps
80 MHz
0x27
100 kbps
0x09
400 kbps
0x03
1000 kbps
100 MHz
0x31
100 kbps
0x0C
385 kbps
0x04
1000 kbps
120 MHz
0x3B
100 kbps
0xE
400 kbps
0x5
1000 kbps