Maple Mini

This page is a general resource for information specific to the Maple Mini. The Maple Mini is a smaller version of the Maple that fits on a breadboard.

Technical Specifications

• MCU: STM32F103CBT6, a 32-bit ARM Cortex M3 microprocessor
• Clock Speed: 72 MHz
• 128 KB Flash and 20 KB SRAM
• 34 digital I/ pins (GPIOs)
• 12 PWM pins at 16 bit resolution
• 9 analog input (ADC) pins at 12 bit resolution
• 2 SPI peripherals
• 2 I2C peripherals
• 7 Channels of Direct Memory Access (DMA) (dma.h)
• 3 USART (serial port) peripherals
• 1 advanced and 3 general-purpose timers
• Dedicated USB port for programming and communications
• JTAG
• Nested Vectored Interrupt Controller (NVIC) (including external interrupt on GPIOs)
• Supplies up to 500 mA at 3.3 V, with separate 250 mA digital and analog regulators for low-noise analog performance
• Open source, four layer design
• Support for low power, sleep, and standby modes (<500 μA)
• Operating Voltage: 3.3 V
• Input Voltage (recommended): 3 V — 12 V
• Dimensions: 2.02″ × 0.72″

Powering the Maple Mini

You can power the Maple Mini via the USB plug or by powering Vin directly.

Warning

The silkscreen on the Maple Mini suggests it will accept an input voltage up to 16 V. We recommend applying no greater than 12 V, and potentially even lower depending upon the current draw requirements of the application. Please see Power Regulation on the Maple Mini for more information.

Power Regulation on the Maple Mini

Power regulation on the Maple is provided by two low dropout linear voltage regulators. (The part is the MCP1703 from Microchip, in the SOT-23A package. You can download the datasheet here ). One of the regulators supplies power to the digital voltage plane; the other supplies power to the analog voltage plane.

These voltage regulators nominally take an input of up to 16V. In addition, while the maximum continuous output current for the board is 250mA, if you are powering the board off higher voltages the amount current it can supply goes down, due to the regulators needing to dissipate the extra power. So if you are powering the board off 12V, the max current is about 40mA at room temperature. In general (again, at room temperature) the max power dissipation (PD) for the chip is about .37W, and output current = PD/(Vin-Vout). For exact max current calculations, please refer to the datasheet linked above.

If you are planning to draw a lot of current from the Maple board, it is necessary to provide input power as close to 3.3V as possible. Powering the microcontroller circuitry and LEDs on the board alone takes approximately 30mA, so if you are powering the board with 12V that leaves only 10mA (at best) available for powering any user circuitry. Attempting to draw more than 10mA runs the risk of shorting out the power regulators and bricking your board.

GPIO Information

The Maple Mini features 34 total input/output pins, numbered D0 through D33. These numbers correspond to the numeric values next to each header on the Maple Mini’s silkscreen. However, some of them have special uses by default [1].

Pin D23 is the USB D+ line, and D24 is the USB D- line. To use them as GPIOs, your program will need to disable SerialUSB first. Be aware, however, that disabling SerialUSB means that the bootloader won’t work properly, and you’ll need to use Perpetual Bootloader Mode to make your next upload.

Pin D32 is the Mini’s button pin. It is thus mainly useful as an input. The pin will read HIGH when the button is pressed.

Pin D33 is the Mini’s LED pin. It is thus mainly useful as an output. The LED will glow when HIGH is written to it. (It also supports PWM, for finer-grained brightness control).

Master Pin Map

This table shows a summary the available functionality on every GPIO pin, by peripheral type. The “5 V?” column documents whether or not the pin is 5 volt tolerant.

Note that this table is not exhaustive; on some pins, more peripherals are available than are listed here.

Pin	GPIO	ADC	Timer	I2C	UART	SPI	5 V?
D0	PB11			2_SDA	3_RX		Yes
D1	PB10			2_SCL	3_TX		Yes
D2	PB2						Yes
D3	PB0	CH8	3_CH3
D4	PA7	CH7	3_CH2			1_MOSI
D5	PA6	CH6	3_CH1			1_MISO
D6	PA5	CH5				1_SCK
D7	PA4	CH4			2_CK	1_NSS
D8	PA3	CH3	2_CH4		2_RX
D9	PA2	CH2	2_CH3		2_TX
D10	PA1	CH1	2_CH2		2_RTS
D11	PA0	CH0	2_CH1_ETR		2_CTS
D12	PC15
D13	PC14
D14	PC13
D15	PB7		4_CH2	1_SDA			Yes
D16	PB6		4_CH1	2_SCL			Yes
D17	PB5			1_SMBA
D18	PB4						Yes
D19	PB3						Yes
D20	PA15						Yes
D21	PA14						Yes
D22	PA13						Yes
D23	PA12		1_ETR		1_RTS		Yes
D24	PA11		1_CH4		1_CTS		Yes
D25	PA10		1_CH3		1_RX		Yes
D26	PA9		1_CH2		1_TX		Yes
D27	PA8		1_CH1		1_CK		Yes
D28	PB15					2_MOSI	Yes
D29	PB14				3_RTS	2_MISO	Yes
D30	PB13				3_CTS	2_SCK	Yes
D31	PB12		1_BKIN	2_SMBA	3_CK	2_NSS	Yes
D32	PB8		4_CH3				Yes
D33	PB1	CH9	3_CH4

GPIO Port Pin Map

The following table shows what pins are associated with each GPIO port.

GPIOA	GPIOB	GPIOC
PA0: D11	PB0: D3	PC0: -
PA1: D10	PB1: D33	PC1: -
PA2: D9	PB2: D2	PC2: -
PA3: D8	PB3: D19	PC3: -
PA4: D7	PB4: D18	PC4: -
PA5: D6	PB5: D17	PC5: -
PA6: D5	PB6: D16	PC6: -
PA7: D4	PB7: D15	PC7: -
PA8: D27	PB8: D32	PC8: -
PA9: D26	PB9: -	PC9: -
PA10: D25	PB10: D1	PC10: -
PA11: D24	PB11: D0	PC11: -
PA12: D23	PB12: D31	PC12: -
PA13: D22	PB13: D30	PC13: D14
PA14: D21	PB14: D29	PC14: D13
PA15: D20	PB15: D28	PC15: D12

Timer Pin Map

The following table shows what pins are associated with a particular timer’s capture/compare channels.

Timer	Ch. 1	Ch. 2	Ch. 3	Ch. 4
1	D27	D26	D25	D24
2	D11	D10	D9	D8
3	D5	D4	D3	D33
4	D16	D15	D32

EXTI Line Pin Map

The following table shows which pins connect to which EXTI lines.

EXTI Line	Pins
EXTI0	D3, D11
EXTI1	D10, D33
EXTI2	D2, D9
EXTI3	D8, D19
EXTI4	D7, D18
EXTI5	D6, D17
EXTI6	D5, D16
EXTI7	D4, D15
EXTI8	D27, D32
EXTI9	D26
EXTI10	D1, D25
EXTI11	D0, D24
EXTI12	D23, D31
EXTI13	D14, D22, D30
EXTI14	D13, D21, D29
EXTI15	D12, D20, D28

USART Pin Map

The Maple Mini has three serial ports (also known as USARTs). They communicate using the pins given in the following table.

Serial Port	TX	RX	CK	CTS	RTS
Serial1	D26	D25	D27	D24	D23
Serial2	D9	D8	D7	D11	D10
Serial3	D1	D0	D31	D30	D29

Low-Noise ADC Pins

Maple Mini has an electrically isolated analog power plane with its own regulator, and a geometrically isolated ground plane, connected to the digital plane by an inductor. Its analog input pins, D3 — D11, are laid out to correspond with these analog planes, and our measurements indicate that they generally offer low noise ADC performance. However, analog performance may vary depending upon the activity of the other GPIOs. Consult the Maple Mini hardware design files for more details.

Board-Specific Values

This section lists the Maple Mini’s board-specific values.

• CYCLES_PER_MICROSECOND: 72
• BOARD_BUTTON_PIN: 32
• BOARD_LED_PIN: 33
• BOARD_NR_GPIO_PINS: 34
• BOARD_NR_PWM_PINS: 12
• boardPWMPins: 3, 4, 5, 8, 9, 10, 11, 15, 16, 25, 26, 27
• BOARD_NR_ADC_PINS: 9
• boardADCPins: 3, 4, 5, 6, 7, 8, 9, 10, 11
• BOARD_NR_USED_PINS: 4
• boardUsedPins: BOARD_LED_PIN, BOARD_BUTTON_PIN, 23, 24 (23 and 24 are used by USB)
• BOARD_NR_USARTS: 3
• BOARD_USART1_TX_PIN: 26
• BOARD_USART1_RX_PIN: 25
• BOARD_USART2_TX_PIN: 9
• BOARD_USART2_RX_PIN: 8
• BOARD_USART3_TX_PIN: 1
• BOARD_USART3_RX_PIN: 0
• BOARD_NR_SPI: 2
• BOARD_SPI1_NSS_PIN: 7
• BOARD_SPI1_MOSI_PIN: 4
• BOARD_SPI1_MISO_PIN: 5
• BOARD_SPI1_SCK_PIN: 6
• BOARD_SPI2_NSS_PIN: 31
• BOARD_SPI2_MOSI_PIN: 28
• BOARD_SPI2_MISO_PIN: 29
• BOARD_SPI2_SCK_PIN: 30
• BOARD_JTMS_SWDIO_PIN: 22
• BOARD_JTCK_SWCLK_PIN: 21
• BOARD_JTDI_PIN: 20
• BOARD_JTDO_PIN: 19
• BOARD_NJTRST_PIN: 18

Hardware Design Files

The hardware schematics and board layout files are available in the Maple Mini GitHub repository.

From the GitHub repository main page, you can download the entire repository by clicking the “Download” button. If you are familiar with Git, you can also clone the repository at the command line with

$ git clone git://github.com/leaflabs/maplemini.git

Failure Modes

The following known failure modes apply to all Maple boards. The failure modes aren’t design errors, but are easy ways to break or damage your board permanently.

• High voltage on non-tolerant pins: not all header pins are 5 V compatible; so e.g. connecting certain serial devices in the wrong way could over-voltage the pins. The pin-mapping master table details which pins are 5 V-tolerant.

Errata

This section lists known issues and warnings for the Maple Mini Rev 2 (the first Rev sold to the public).

• Silkscreen Vin voltage mistake: The silkscreen on the Maple Mini falsely indicates that Vin may be supplied with up to 16V. We recommend an input voltage no greater than 12V, and potentially even lower depending upon the current draw requirements of the application. Please see Power Regulation on the Maple Mini for more information.

Recommended Reading

STMicro documentation for STM32F103CB microcontroller:

• Datasheet (PDF); covers STM32F103x8, STM32F103xB.
• Reference Manual RM0008 (PDF); definitive resource for peripherals on the STM32F1 line.
• Programming Manual PM0056 (PDF); assembly language and register reference.
• STM32F103CB overview page with links to further references.

Footnotes

[1]	See boardUsedPins for more information.