receive a Quick Command, it should be expecting such a command because it must write the
I2CSDR
with a specific value when
R/S
is set.
18.3.2
Available Speed Modes
The I
2
C bus can run in Standard mode (100 kbps), Fast mode (400 kbps), Fast mode plus (1 Mbps)
or High-Speed mode (3.4 Mbps, provided correct system clock frequency is set and there is
appropriate pull strength on SCL and SDA lines). The selected mode should match the speed of
the other I
2
C devices on the bus.
18.3.2.1
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 page 1313). This value is
determined by replacing the known variables in the equation below and solving for
TIMER_PRD
.
The I
2
C clock period is calculated as follows:
SCL_PERIOD
= 2 × (1 +
TIMER_PRD
) × (
SCL_LP
+
SCL_HP
) ×
CLK_PRD
For example:
CLK_PRD
= 50 ns
TIMER_PRD
= 2
SCL_LP
=6
SCL_HP
=4
yields a SCL frequency of:
1/
SCL_PERIOD
= 333 Khz
Table 18-2 gives 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 18-2. Examples of I
2
C Master Timer Period Versus Speed Mode
Fast Mode
Plus
Timer
Period
Fast Mode
Timer Period
Standard Mode
Timer Period
System Clock
-
-
-
-
100 Kbps
0x01
4 MHz
-
-
-
-
100 Kbps
0x02
6 MHz
-
-
312 Kbps
0x01
89 Kbps
0x06
12.5 MHz
-
-
278 Kbps
0x02
93 Kbps
0x08
16.7 MHz
-
-
333 Kbps
0x02
100 Kbps
0x09
20 MHz
-
-
312 Kbps
0x03
96.2 Kbps
0x0C
25 MHz
-
-
330 Kbps
0x04
97.1 Kbps
0x10
33 MHz
June 18, 2014
1284
Texas Instruments-Production Data
Inter-Integrated Circuit (I
2
C) Interface