Introduction

GPIO means General Purporse Input/Output and is the generic name for all the pins of the AVR32UC3A microcontroller. Every pin of the microcontroller is a GPIO pin except for the power supply pins, the pin that resets the processor and the USB JTAG signal connections. This includes the connections to the SDRAM and every other input or output signal.

Each of the GPIO pins can be programmed to have one of three functions, and the three functions are different for every pin. When the Mizar32 is turned on, it is deaf and blind and the first thing that the on-board software must do is to program the correct function for each of the GPIO pins that are necessary for it to be able to talk to the rest of the world.

For example, Hempl does the following when it starts up:

it programs the pins that are connected to the oscillator crystals to function as oscillator inputs. This increases its processing speed from 115kHz (its internal oscillator) to 66MHz (the external oscillator). It also programs the pins connected to the 32768Hz crystal as oscillator inputs so that it can measure time accurately;
it programs the LCDpins connected to the SDRAM memory to work as SDRAM memory pins so that, as well as the 64Kbyte (Models A and B) or 32Kbyte (Model C) internal RAM, it can also access the 32Mbyte SDRAM memory chip;
if you have configured the Hempl console to be on the serial port, it programs UART0's RX and TX pins to talk RS232;
if your Hempl firmware includes MMC/SD card support, the pins of the second SPI port, SPI1, are programmed to talk the MMC/SD card.

The GPIO pins for all other devices are programmed to perform their function the first time you call them from Lua. If you are not using some device you are free to use its GPIO pins as simple input/output pins: see the PIO section for further details on how to do this.

Pin functions

On the Mizar32, the following functions are assigned to the GPIO pins:

Legend:

X = Pin is not connected to anything
Foo/Bar = signal is used for more than one thing

Port A
PIN	SIGNAL	Description	Bus pin
PA00	UART0_RX	Right bus serial port	BUS4 pin 3
PA01	UART0_TX	Right bus serial port	BUS4 pin 4
PA02	GPIO2	Bus GPIO, 4mA max, VGA SRAM /HOLD pin	BUS5 pin 11
PA03	UART0_RTS	Right bus serial port	BUS4 pin 5
PA04	UART0_CTS	Right bus serial port	BUS4 pin 6
PA05	UART1_RX	Left bus serial port	BUS3 pin 3
PA06	UART1_TX	Left bus serial port	BUS3 pin 4
PA07	GPIO7	Bus GPIO, 4mA max	BUS5 pin 12
PA08	UART1_RTS	Left bus serial port	BUS3 pin 10
PA09	UART1_CTS	Left bus serial port	BUS3 pin 9
PA10	SPI0_CS0	Left bus SPI	BUS1 pin 12
PA11	SPI0_MISO		BUS1 pin 13
PA12	SPI0_MOSI		BUS1 pin 14
PA13	SPI0_SCK		BUS1 pin 15
PA14	SPI1_CS0	SD card chip select	None
PA15	SPI1_SCK	Right bus SPI/SD card clock	BUS4 pin 9
PA16	SPI1_MOSI	Right bus SPI/SD card data in (host->card)	BUS4 pin 10
PA17	SPI1_MISO	Right bus SPI/SD card data out (card->host)	BUS4 pin 11
PA18	SPI1_CS1	"FREE"	None
PA19	SPI1_CS2	Right bus SPI chip select	BUS4 pin 12
PA20	EXT_INT	?	BUS5 pin 13
PA21	ADC0	ADC	BUS5 pin 5
PA22	ADC1		BUS5 pin 6
PA23	ADC2		BUS5 pin 7
PA24	ETHERNET	Ethernet interrupt	BUS2 pin 3
PA25	ADC4	ADC	BUS6 pin 4
PA26	ADC5		BUS6 pin 5
PA27	ADC6		BUS6 pin 6
PA28	ADC7		BUS6 pin 7
PA29	SDA	I2C	BUS2 pin 10
PA30	SCL	I2C	BUS2 pin 11

Port B
PIN	SIGNAL	Description	Bus pin
PB00	REF_CLK	Ethernet	BUS1 pin 3
PB01	TX_EN		BUS1 pin 4
PB02	TX0		BUS1 pin 5
PB03	TX1		BUS1 pin 6
PB04	X		None
PB05	RX0		BUS2 pin 5
PB06	RX1		BUS2 pin 6
PB07	RX_ER		BUS2 pin 7
PB08	MDC		BUS2 pin 4
PB09	MDIO		BUS2 pin 8
PB10	SDCK	SDRAM	None
PB11	SDCKE		None
PB12	RASn		None
PB13	CASn		None
PB14	SDWEn		None
PB15	RX_DV	Ethernet	BUS1 pin 7
PB16	SDA10	SDRAM A10	None
PB17	GPIO49	Bus GPIO, 4mA max	BUS5 pin 8
PB18	GPIO50/PWM6	Bus GPIO, 4mA max/PWM channel 6	BUS5 pin 9
PB19	PWM0	PWM	BUS4 pin 7
PB20	PWM1		BUS4 pin 8
PB21	PWM2		None
PB22	PWM3		BUS6 pin 1
PB23	UART1_DCD	Left bus serial port	BUS3 pin 5
PB24	UART1_DSR		BUS3 pin 6
PB25	UART1_DTR		BUS3 pin 7
PB26	UART1_RI		BUS3 pin 8
PB27	PWM4	PWM channel 4	BUS6 pin 2
PB28	PWM5	PWM channel 4	BUS6 pin 3
PB29	GPIO61/LED	On-board LED (0=lit)	None
PB30	GPIO62	Bus GPIO, 4mA max	BUS6 pin 9
PB31	GPIO63	Bus GPIO, 4mA max	BUS6 pin 10

Port C
PIN	SIGNAL	Description
PC00	Xin32	32768Hz crystal "X2" (*)
PC01	Xout32	32768Hz crystal "X2" (*)
PC02	Xin0	12MHz crystal "X1"
PC03	Xout0	12MHz crystal "X1"
PC04	Xin1	Not used
PC05	Xout1	Not used

) On circuit pads C47 before Mizar32 v1.3.2

Port X
PIN	SIGNAL	Description	Bus pin
PX00	D10	SDRAM	None
PX01	D9
PX02	D8
PX03	D7
PX04	D6
PX05	D5
PX06	D4
PX07	D3
PX08	D2
PX09	D1
PX10	D0
PX11	DQM1
PX12	X
PX13	X
PX14	CS1n
PX15	X
PX16	GPIO88/BUTTON	Bus GPIO/Push button on main board (low when pressed)	BUS6 pin 13
PX17	A17	SDRAM BA1	None
PX18	A16	SDRAM BA0	None
PX19	GPIO85	Bus GPIO, 4mA max	BUS6 pin 12
PX20	A14	SDRAM A12	None
PX21	A13	SDRAM A11	None
PX22	GPIO82	Bus GPIO, 4mA max (SDRAM A10 is on PB16)	BUS6 pin 11
PX23	A11	SDRAM A9	None
PX24	A10	SDRAM A8
PX25	A9	SDRAM A7
PX26	A8	SDRAM A6
PX27	A7	SDRAM A5
PX28	A6	SDRAM A4
PX29	A5	SDRAM A3
PX30	A4	SDRAM A2
PX31	A3	SDRAM A1
PX32	A2	SDRAM A0
PX33	GPIO71	Bus GPIO, 4mA max	BUS5 pin 10
PX34	DQM0	SDRAM	None
PX35	D15
PX36	D14
PX37	D13
PX38	D12
PX39	D11

Bus renaming:
In Mizar32 v1.3.2, the bus connectors were renamed

Old	New	Also known as
P3	BUS1	BUS_HALF_LEFT_UP
P4	BUS2	BUS_HALF_LEFT_DOWN
P2	BUS3	BUS_HALF_LEFT_EXT
P5	BUS4	BUS_HALF_RIGHT_UP
P6	BUS5	BUS_HALF_RIGHT_DOWN
P7	BUS6	BUS_HALF_RIGHT_EXT

Introduction

Pin functions

Further reading