STM32F107VC/GPIO

General Purpose and Alternate Function I/O

Standard GPIO I/O bit

5 volt tolerant GPIO I/O bit

GPIO functional description

Each of the general-purpose I/O ports has two 32-bit configuration registers (GPIOx_CRL, GPIOx_CRH), two 32-bit data registers (GPIOx_IDR, GPIOx_ODR), a 32-bit set/reset register (GPIOx_BSRR), a 16-bit reset register (GPIOx_BRR) and a 32-bit locking register (GPIOx_LCKR).

Subject to the specific hardware characteristics of each I/O port listed in the datasheet, each port bit of the General Purpose IO (GPIO) Ports, can be individually configured by software in several modes:

• Input floating
• Input pull-up
• Input-pull-down
• Analog
• Output open-drain
• Output push-pull
• Alternate function push-pull
• Alternate function open-drain

Each I/O port bit is freely programmable, however the I/O port registers have to be accessed as 32-bit words (half-word or byte accesses are not allowed). The purpose of the GPIOx_BSRR and GPIOx_BRR registers is to allow atomic read/modify accesses to any of the GPIO registers. This way, there is no risk that an IRQ occurs between the read and the modify access.

Default configuration

During and just after reset, the alternate functions are not active and the I/O ports are configured in Input Floating mode.

Port Bit Configuration

Each bit can be configured using the configuration registers shown below

GPIO Configuration Registers. (Note:x = Port A to G )

Name	Section	Name	r/w	Bits	Function
GPIOx_CRL	9.2.1	Port configuration register low	rw	CNF[1,0], MODE[1,0]	Configure lowest 8 bit of port x. IN or OUT
GPIOx_CRH	9.2.2	Port configuration register high	rw	CNF[1,0], MODE[1,0]	Configure highest 8 bit of port x. IN or OUT
GPIOx_IDR	9.2.3	port input data register	r	IDR[15:0]	Read state of pins configured for input on port x (Lowest 16 bits of word)
GPIOx_ODR	9.2.4	port output data register	rw	ODR[15:0]	Write to pins configured for Output on port x (Lowest 16 bits of word)
GPIOx_BSRR	9.2.5	Port bit set/reset register	w	BS[15:0], BR[15:0]	Atomic Set/Reset individual Pins configured for Output.
GPIOx_BRR	9.2.6	Port bit reset register	w	BR[15:0]	Atomic Reset individual Pins configured for Output. (Lowest 16 bits of word)
GPIOx_LCKR	9.2.7	Port configuration lock register	rw	LCK[15:0], LCKK	Lock individual pins of port x (Freeze CRL and CRH of ports)

Port bit configuration table

Configuration mode		CNF1	CNF0	MODE1	MODE0	PxODR register
General Purpose Output	Push-Pull	0	0	01 10 11 See Mode below		0 or 1
	Open Drain	1	0 or 1
Alternate function Output	Push-Pull	1	0	Don't Care
	Open Drain	1	Don't Care
Input	Analog	0	0	00		Don't Care
	Input Floating	1	Don't Care
	Input Pull-Down	1	0	0
	Input Pull-Up			1

Output MODE bits.

MODE[1:0]	Meaning
00	Reserved
01	Max. output speed 10 MHz
10	Max. output speed 2 MHz
11	Max. output speed 50 MHz

Detailed description

For detailed description of GPIO see STM32F107VC Reference Manual Chapter 9.