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Electrical characteristics STM32WLE5J8/JB/JC
122/135 DS13105 Rev 4
5.3.26 Communication interfaces characteristics
I
2
C interface
characteristics
The I
2
C interface meets the timings requirements of the I
2
C-bus specification and user
manual rev. 03 for:
Standard-mode (Sm): bitrate up to 100 Kbit/s
Fast-mode (Fm): bitrate up to 400 Kbit/s
Fast-mode Plus (Fm+): bitrate up to 1 Mbit/s
The I
2
C timings requirements are guaranteed by design when the I2C peripheral is properly
configured (refer to the reference manual) and when the II2CCLK frequency is greater than
the minimum shown in the table below.
The SDA and SCL I/O requirements are met with the following restrictions:
The SDA and SCL I/O pins are not “true” open-drain. When configured as open-drain,
the PMOS connected between the I/O pin and V
DDIOx
is disabled, but is still present.
The 20 mA output drive requirement in Fast-mode Plus is partially supported. This
limits the maximum load C
load
supported in Fast-mode Plus, given by these formulas:
–t
r
(SDA/SCL) = 0.8473 x R
p
x C
load
–R
p
(min) = [V
DD
- V
OL
(max)] / I
OL
(max)
where R
p
is the I2C lines pull-up. Refer to Section 5.3.16: I/O port characteristics
for more details.
Table 83. IWDG min/max timeout period at 32 kHz (LSI)
(1)
Prescaler divider PR[2:0] bits Min timeout (RL[11:0] = 0x000) Max timeout (RL[11:0] = 0xFFF) Unit
/4 0x0 0.125 512
ms
/8 0x1 0.250 1024
/16 0x2 0.500 2048
/32 0x3 1.0 4096
/64 0x4 2.0 8192
/128 0x5 4.0 16384
/256 0x6 or 0x7 8.0 32768
1. The exact timings still depend on the phasing of the APB interface clock versus the LSI clock, hence there is always a full
RC period of uncertainty.
Table 84. Minimum I2CCLK frequency in all I2C modes
Symbol Parameter Conditions Min Unit
f
(I2CCLK)
I2CCLK frequency
Standard-mode - 2
MHz
Fast-mode
Analog filter ON, DNF = 0 8
Analog filter OFF, DNF = 1 9
Fast-mode Plus
Analog filter ON, DNF = 0 18
Analog filter OFF, DNF = 1 16