Figure 3. Output Buffer And Current Flow; Figure 4. Logical Level Compatibility - ST STM32 Application Note

AN4899
In case of communication exchange, STM32 output signals must be compatible with the
V / V
IL IH
the transmitter device as shown in
V
OHmin
V
OLmax
For the CMOS technology, the input threshold voltages are relative to V
V ~ 2 / 3 V
IHmin
For the TTL technology, the levels are fixed and equal to V
The V
OH
general input/output characteristics given in the STM32 datasheet.

Figure 3. Output buffer and current flow

VDD
DATA FROM
CORE
'1'
Ouput
control
'0'
GND
of the receptor device and STM32 inputs must be compliant with the V

Figure 4. Logical level compatibility

Output
V
DDIO
High level = 1
Intermediate region
Low level = 0
0 V
and V ~ 1 / 3 V
DD ILmax
,V , V , V levels and the values of output-driving currents are part of the
OL IH IL
GPIO electrical characteristics and definitions
I
OH
ON
OFF
EXTERNAL
OFF
ON
I
OL
Figure 4.
V
DDIO
Noise margin
Noise margin
0 V
.
DD
AN4899 Rev 3
PAD
MSv46874V2
Input
High level = 1
Intermediate region
Low level = 0
as follows:
DD
= 2V and V
IHmin ILmax
/ V of
OL OH
V
IHmin
V
ILmax
MSv46875V2
= 0.8 V.
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