GPIO

1. GPIO and Clock
Configuration

2. GPIO Interface
GPIO Output:
LED
LCD
7 –segment
GPIO Input:
Key/switch
Keypad

3. What are the GPIO Configuration
parameters???

4. GPIO Configuration
GPIO_Input / GPIO_Output
GPIO_Output:
GPIO_Output level: Low/High
GPIO mode: Output push pull or open drain
GPIO pull-up/pull-down: pull-up / pull-down / no pull-up no pull-
down
Maximum Output Speed: Low / Medium / High

5. GPIO Configuration
What is Push-Pull &
What is Open Drain????

6. GPIO Configuration:
Push pull
• Two MOSFETs: one connected toVcc & other
connected to Ground
• Output goes Low, it is connected to ground
through n-channel MOSFET
• Output goes High, it is connected toVcc
through p-channel MOSFET
• Output  Low, actively ‘pulled’ to Ground
• Output  High, actively ‘pushed’ toVcc

7. GPIO Configuration:
Push pull

8. GPIO Configuration:
OPEN Drain
• Only one MOSFET; only n-channel MOSFET
• Drain of MOSFET taken out of IC
• Only active in one direction
• It can pull the towards Ground
• Cannot drive toVcc (High)
• Switch OFF  Output Floating
• Needs a Pull-up resistor

9. GPIO Configuration:
Pull-up / pull-down
• In Digital circuits, pin must be connected to
either HIGH or LOW
• Pin should not be left unconnected (floating)
• When floating, undetermined state (can be
HIGH or LOW or not both)
• To Correct, connect a resistor from signal line
toVcc or Ground
• Resistor will either pull-up signal pin toVcc
• Or pull-down to Ground
Pull-up
resistor
Pull-down
resistor
Output

10. GPIO Configuration:
GPIO Speed
• Controls the slew rate
• Rise time and fall time of output signal
• Good practice to keep slow slew rate
• Increase only when needed

11. GPIO Configuration:
GPIO Input
• Input with internal pull-up; input signal pulled-up toVcc
• Input with internal pull-down ; input signal pulled-down to
Ground
• Floating Input; Signal level follows the external signal
• No external signal; Schmitt trigger toggles between logical levels
induced by external noise on pin