Maple¶

Contents

Technical Specifications ¶

MCU: STM32F103RBT6, a 32-bit ARM Cortex M3 microprocessor

Clock Speed: 72 MHz

128KB Flash and 20KB SRAM

43 Digital I/O Pins (GPIO)

16 Analog Input Pins, 12-bit ADC resolution (ADC)

15 PWM pins at 16-bit resolution (PWM)

Dedicated USB port for programming and communications (USB)

External JTAG interface (JTAG)

64 Channel nested vector interrupt handler (including external interrupt on GPIOs)

Integrated SPI (SPI)

Integrated I2C (I2C)

7 Channels of Direct Memory Access (DMA) (dma.h)

3 USART divices (USART)

Four 4-channel timers (Timers)

Supplies up to 500mA @ 3.3v (with separate 250 mA digital and analog regulators)

Support for low power, sleep, and standby modes (<500uA)

Operating Voltage: 3.3V

Input Voltage (recommended): 3V-12V

Dimensions are 2.05″x2.1″

We went through three versions (“Revs”) of the Maple hardware: Rev 1, Rev 3, and Rev 5 [1]; Rev 5, the final design, is currently on sale. The following sections will help you to help you identify your Rev.

Rev 5 ¶

These boards went on sale in November 2010. They have white buttons, and “r5” in small print near the “LeafLabs Maple” text next to the “infinity leaf” logo. The Maple Rev 5 repositioned the double header on the right hand side to better fit 0.1 inch pitch breadboard. This necessitated the removal of pins 21 and 22 from the double header; they are still available, but don’t have any headers installed on them.

Rev 3 ¶

This batch of boards went on sale beginning in May 2010. They have a darker red silkscreen and the “infinity leaf” logo. The Maple Rev 3 was the first version which includes the built-in button, labeled BUT. It also includes a built-in LiPo battery charger.

Rev 1 ¶

A small number of Maple Rev 1 boards went on sale in late 2009. They have a light red silkscreen and a single pixelated leaf as a logo.

Powering the Maple ¶

The Maple’s power source is determined by the header to the left of the “LeafLabs” label on the silkscreen. All versions of the Maple can be powered from the barrel jack connector, USB, or a LiPo battery. We ship the Maple with a jumper on the USB selector. In order to power it off of an alternative source, unplug the Maple, then move the jumper to the desired selector before reconnecting power.

You can also power the Maple via the pin labeled “Vin” on the lower header. However, don’t do this while simultaneously powering the Maple from another source, or you could damage the board.

Using the Built-in Battery Charger ¶

Maples Rev 3 and Rev 5 also have a built-in LiPo battery charger. In order to use it, put a jumper across the CHRG header on the power selection header and across the USB, or EXT selectors, depending on whether you’re charging the battery via USB cable or barrel jack connector. The LED labeled CHRG will light up while the battery is being charged. When the battery is finished charging, the LED labeled DONE will also light up.

GPIO Information ¶

The Maple features 38 ready-to-use general purpose input/output (see GPIO) pins for digital input/output, numbered D0 through D37. These numbers correspond to the numeric values next to each header on the Maple silkscreen.

Pin D38 is the board’s button pin. It is thus mainly useful as an input. The pin will read HIGH when the button is pressed.

More GPIOs (numbered D39–D42) are available if you use the disableDebugPorts() function; see the board-specific debug pin constants for more information. (See this erratum for information about the pin numbered 43 on the silkscreen).

Master Pin Map ¶

This table shows the available functionality on every GPIO pin, by peripheral type. The “STM32” column refers to the port and number that the header is connected to on the microcontroller. The “5V?” column documents whether or not the pin is 5 volt tolerant.

Pin	STM32	ADC	Timer	I2C	UART	SPI	5v?
D0	PA3	ADC3	TIM2_CH4		USART2_RX
D1	PA2	ADC2	TIM2_CH3		USART2_TX
D2	PA0	ADC0	TIM2_CH1_ETR		USART2_CTS
D3	PA1	ADC1	TIM2_CH2		USART2_RTS
D4	PB5			ISC1_SMBA
D5	PB6		TIM4_CH1	I2C1_SCL			Yes
D6	PA8		TIM1_CH1		USART1_CK		Yes
D7	PA9		TIM1_CH2		USART1_TX		Yes
D8	PA10		TIM1_CH3		USART1_RX		Yes
D9	PB7		TIM4_CH2	I2C1_SDA			Yes
D10	PA4	ADC4			USART2_CK	SPI1_NSS
D11	PA7	ADC7	TIM3_CH2			SPI1_MOSI
D12	PA6	ADC6	TIM3_CH1			SPI1_MISO
D13	PA5	ADC5				SPI1_SCK
D14	PB8		TIM4_CH3				Yes
D15	PC0	ADC10
D16	PC1	ADC11
D17	PC2	ADC12
D18	PC3	ADC13
D19	PC4	ADC14
D20	PC5	ADC15
D21	PC13
D22	PC14
D23	PC15
D24	PB9		TIM4_CH4				Yes
D25	PD2		TIM3_ETR				Yes
D26	PC10						Yes
D27	PB0	ADC8	TIM3_CH3
D28	PB1	ADC9	TIM3_CH4
D29	PB10			I2C2_SCL	USART3_TX		Yes
D30	PB11			I2C2_SDA	USART3_RX		Yes
D31	PB12		TIM1_BKIN	I2C2_SMBA	USART3_CK	SPI2_NSS	Yes
D32	PB13		TIM1_CH1N		USART3_CTS	SPI2_SCK	Yes
D33	PB14		TIM1_CH2N		USART3_RTS	SPI2_MISO	Yes
D34	PB15		TIM1_CH3N			SPI2_MOSI	Yes
D35	PC6						Yes
D36	PC7						Yes
D37	PC8						Yes
D38	PC9						Yes
D39	PA13						Yes
D40	PA14						Yes
D41	PA15						Yes
D42	PB3						Yes

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	D6	D7	D8
2	D2	D3	D1	D0
3	D12	D11	D27	D28
4	D5	D9	D14	D24

EXTI Line Pin Map ¶

The following table shows which pins connect to which EXTI lines on the Maple.

EXTI Line	Pins
EXTI0	2, 15, 27
EXTI1	3, 16, 28
EXTI2	1, 17, 25
EXTI3	0, 18
EXTI4	10, 19
EXTI5	4, 13, 20
EXTI6	5, 12, 35
EXTI7	9, 11, 36
EXTI8	6, 14, 37
EXTI9	7, 25, 28
EXTI10	8, 26, 29
EXTI11	30
EXTI12	31
EXTI13	21, 32
EXTI14	22, 33
EXTI15	23, 34

USART Pin Map ¶

The Maple has three serial ports (also known as a UARTs or USARTs): Serial1, Serial2, and Serial3. They communicate using the pins summarized in the following table:

Serial Port	TX	RX	CK	CTS	RTS
`Serial1`	7	8	6
`Serial2`	1	0	10	2	3
`Serial3`	29	30	31	32	33

Board-Specific Values ¶

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

CYCLES_PER_MICROSECOND: 72
BOARD_BUTTON_PIN: 38
BOARD_LED_PIN: 13
BOARD_NR_GPIO_PINS: 44
BOARD_NR_PWM_PINS: 16
boardPWMPins: 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 14, 24, 25, 27, 28
BOARD_NR_ADC_PINS: 15
boardADCPins: 0, 1, 2, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 27, 28
BOARD_NR_USED_PINS: 7
boardUsedPins: BOARD_LED_PIN, BOARD_BUTTON_PIN, BOARD_JTMS_SWDIO_PIN, BOARD_JTCK_SWCLK_PIN, BOARD_JTDI_PIN, BOARD_JTDO_PIN, BOARD_NJTRST_PIN
BOARD_NR_USARTS: 3
BOARD_USART1_TX_PIN: 7
BOARD_USART1_RX_PIN: 8
BOARD_USART2_TX_PIN: 1
BOARD_USART2_RX_PIN: 0
BOARD_USART3_TX_PIN: 29
BOARD_USART3_RX_PIN: 30
BOARD_NR_SPI: 2
BOARD_SPI1_NSS_PIN: 10
BOARD_SPI1_MOSI_PIN: 11
BOARD_SPI1_MISO_PIN: 12
BOARD_SPI1_SCK_PIN: 13
BOARD_SPI2_NSS_PIN: 31
BOARD_SPI2_MOSI_PIN: 34
BOARD_SPI2_MISO_PIN: 33
BOARD_SPI2_SCK_PIN: 32
BOARD_JTMS_SWDIO_PIN: 39
BOARD_JTCK_SWCLK_PIN: 40
BOARD_JTDI_PIN: 41
BOARD_JTDO_PIN: 42
BOARD_NJTRST_PIN: 43

Hardware Design Files ¶

The hardware schematics and board layout files are available in the Maple Github repository. The design files for Rev 1, Rev 3, and Rev 5 are respectively in the maple-r1, maple-r3, and maple-r5 subdirectories. A schematic for a JTAG adapter suitable for use with Maple is available in the jtagadapter directory.

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/maple.git

Failure Modes ¶

The following are known failure modes. 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 5V 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 5V-tolerant.

Errata ¶

General ¶

Power Supply Marketing Mistake: We originally sold the Maple advertising that it was capable of supplying up to 800 mA; the correct value is 500 mA.

By Rev ¶

The following subsections lists known issues and warnings for each revision of the Maple board.

Rev 5 ¶

Pin 3 AIN missing: Pin 3 is capable of analog input, but on Rev 5s manufactured during Fall 2010, the corresponding “AIN” is missing from its silkscreen. This mistake was fixed in later manufacturing runs.

Reset and PB4 tied together: The Maple’s reset line is also connected to PB4, which is labeled on the silkscreen as pin 43. Thus, attempting to use pin 43 as a GPIO may reset your board. This has other implications. Since PB4 is also the JTAG NJTRST line, this prevents the JTAG “reset halt” command from working properly.

Rev 3 ¶

Pin 3 AIN missing: Pin 3 is capable of analog input, but the corresponding “AIN” is missing from the Rev 3 silkscreen.

Bad/Sticky Buttons: a number of Rev 3 boards sold in May-June 2010 have questionable RESET and BUT buttons.

What seems to have happened is that the flux remover we used to clean the boards before shipping eroded the plastic internals, which resulted in intermittent functionality. All buttons on all shipped boards did function in testing, but some may have been unreliable in regular use.

If you have this problem, we will be happy to ship you new buttons if you think you can re-solder them yourself, or you can ship us your board and we will swap out that part.

For reference, the button part number is KMR211GLFS and the flux remover we used is “Precision Electronics Cleaner” from RadioShack, which is “Safe on most plastics” and contains Dipropylene glycol monomethyl ether, hydrotreated heavy naphtha, dipropylene glycol methyl ether acetate, and carbon dioxide.
Resistors on pins 0 and 1: these header pins, which are RX/TX on USART2 (Serial2), have resistors in-line between the STM32 and the headers. These resistors increase the impedance of the lines for ADC reads and affect the open drain GPIO functionality of the pins.

These resistors were accidentally copied over from older Arduino USB designs, where they appear to protect the USB-Serial converter from TTL voltage on the headers.
Silkscreen Errors: the silkscreen on the bottom indicated PWM functionality on pin 25 and listen the external header GND pin as number 38 (actually 38 is connected to the BUT button). We manually sharpied over both of these mistakes.
PWM Marketing Mistake: We originally sold the Maple advertising 22 channels of 16-bit hardware PWM; actually the Maple only has 15.
Reset and NJTRST tied together: The MCU’s reset pin is tied to PB4, the NJTRST pin, which is pin 43. Thus, attempting to use pin 43 as a GPIO will reset your board (and also prevents the JTAG “reset halt”) command from working properly. It’s possible to cut the trace, but doing so will damage your board, so we do not recommend it unless you’re very sure about what you’re doing.

Rev 1 ¶

ADC noise: generally very high, in particular when the USB port is being used for communications (including keep-alive pings when connected to a computer).

This issue was resolved in Rev 3 with a 4-layer design and a geometrically isolated ADC V_ref plane.
Resistors on pins 0 and 1: these header pins, which are RX/TX on USART2 (Serial2), have resistors in-line between the STM32 and the headers. These resistors increase the impedance of the lines for ADC reads and affect the open drain GPIO functionality of the pins.

These resistors were accidentally copied over from older Arduino USB designs, where they appear to protect the USB-Serial converter from TTL voltage on the headers.
Silkscreen Differences: the pin numbering scheme on Rev 1 is different from Rev 3, and thus Rev 3 software is difficult to use with Rev 1 boards. Notably, the analog input bank is labeled A0-A4 on Rev 1 but 15-20 on Rev 3, and the extra header bank does not have a pinout table on the bottom.
No BUT Button: the BUT button, useful for serial bootloading, was only added in Rev 3. As a workaround, you can directly short the appropriate MCU pin to Vcc; see this forum posting.
PWM Marketing Mistake: We originally sold the Maple advertising 22 channels of 16-bit hardware PWM; the correct number is 15.
Reset and NJTRST tied together: The MCU’s reset pin is tied to PB4, the NJTRST pin, which is pin 43. Thus, attempting to use pin 43 as a GPIO will reset your board (and also prevents the JTAG “reset halt”) command from working properly. It’s possible to cut the trace, but doing so will damage your board, so we do not recommend it unless you’re very sure about what you’re doing.

Maple¶

Technical Specifications ¶

Identifying your Rev ¶

Rev 5 ¶

Rev 3 ¶

Rev 1 ¶

Powering the Maple ¶

Using the Built-in Battery Charger ¶

GPIO Information ¶

Master Pin Map ¶

Timer Pin Map ¶

EXTI Line Pin Map ¶

USART Pin Map ¶

Board-Specific Values ¶

Hardware Design Files ¶

Failure Modes ¶

Errata ¶

General ¶

By Rev ¶

Rev 5 ¶

Rev 3 ¶

Rev 1 ¶

Recommended Reading ¶

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