Maple

This page is a general resource for information specific to the Maple.

Technical Specifications

• MCU: STM32F103RBT6, a 32-bit ARM Cortex M3 microprocessor
• Clock Speed: 72 MHz
• 128 KB Flash and 20 KB SRAM
• 43 digital I/O pins (GPIOs)
• 15 PWM pins at 16 bit resolution
• 15 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
• One advanced and three 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): 4 V — 12 V
• Dimensions: 2.05″ × 2.1″

Identifying your Rev

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.

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. This pin feeds into both the digital and analog voltage regulators. However, don’t do this while simultaneously powering the board from another source, or you could damage it.

When powering the board from a barrel jack, double check the polarity of the barrel. The appropriate polarity is noted on the silkscreen right next to the connector.

Warning

Silkscreens on Maples up through Rev 5s manufactured in Spring 2011 falsely indicated that the barrel jack could be supplied by up to 18V. (Rev5s manufactured after Spring 2011 may still have this error on the silk, but it has been marked over.) We recommend a barrel jack input voltage no greater than 12V, and potentially even lower depending upon the current draw requirements of the application. The same goes for powering off LiPo batteries.

Please see Power Regulation on the Maple for more information.

Power Regulation on the Maple

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 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.

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 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 on the back of the Maple’s silkscreen) 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 a summary of 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	PA3	CH3	2_CH4		2_RX
D1	PA2	CH2	2_CH3		2_TX
D2	PA0	CH0	2_CH1_ETR		2_CTS
D3	PA1	CH1	2_CH2		2_RTS
D4	PB5			1_SMBA
D5	PB6		4_CH1	1_SCL			Yes
D6	PA8		1_CH1		1_CK		Yes
D7	PA9		1_CH2		1_TX		Yes
D8	PA10		1_CH3		1_RX		Yes
D9	PB7		4_CH2	1_SDA			Yes
D10	PA4	CH4			2_CK	1_NSS
D11	PA7	CH7	3_CH2			1_MOSI
D12	PA6	CH6	3_CH1			1_MISO
D13	PA5	CH5				1_SCK
D14	PB8		4_CH3				Yes
D15	PC0	CH10
D16	PC1	CH11
D17	PC2	CH12
D18	PC3	CH13
D19	PC4	CH14
D20	PC5	CH15
D21	PC13
D22	PC14
D23	PC15
D24	PB9		4_CH4				Yes
D25	PD2		3_ETR				Yes
D26	PC10						Yes
D27	PB0	CH8	3_CH3
D28	PB1	CH9	3_CH4
D29	PB10			2_SCL	3_TX		Yes
D30	PB11			2_SDA	3_RX		Yes
D31	PB12			2_SMBA	3_CK	2_NSS	Yes
D32	PB13				3_CTS	2_SCK	Yes
D33	PB14				3_RTS	2_MISO	Yes
D34	PB15					2_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

GPIO Port Pin Map

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

GPIOA	GPIOB	GPIOC
PA0: D2	PB0: D27	PC0: D15
PA1: D3	PB1: D28	PC1: D16
PA2: D1	PB2: -	PC2: D17
PA3: D0	PB3: D42	PC3: D18
PA4: D10	PB4: D43	PC4: D19
PA5: D13	PB5: D4	PC5: D20
PA6: D12	PB6: D5	PC6: D35
PA7: D11	PB7: D9	PC7: D36
PA8: D6	PB8: D14	PC8: D37
PA9: D7	PB9: D24	PC9: D38
PA10: D8	PB10: D29	PC10: D26
PA11: -	PB11: D30	PC11: -
PA12: -	PB12: D31	PC12: -
PA13: D39	PB13: D32	PC13: D21
PA14: D40	PB14: D33	PC14: D22
PA15: D41	PB15: D34	PC15: D23

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	D2, D15, D27
EXTI1	D3, D16, D28
EXTI2	D1, D17, D25
EXTI3	D0, D18, D42
EXTI4	D10, D19
EXTI5	D4, D13, D20
EXTI6	D5, D12, D35
EXTI7	D9, D11, D36
EXTI8	D6, D14, D37
EXTI9	D7, D25, D28
EXTI10	D8, D26, D29
EXTI11	D30
EXTI12	D31
EXTI13	D21, D32, D39
EXTI14	D22, D33, D40
EXTI15	D23, D34, D41

USART Pin Map

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

Serial Port	TX	RX	CK	CTS	RTS
Serial1	D7	D8	D6
Serial2	D1	D0	D10	D2	D3
Serial3	D29	D30	D31	D32	D33

Low-Noise ADC Pins

The six pins at the bottom right of the board (D15—D20) generally offer lower-noise ADC performance than other pins on the board. If you’re concerned about getting good ADC readings, we recommend using one of these pins to take your measurements.

Maple has an electrically isolated analog power plane with its own regulator, and a geometrically isolated ground plane. Pins D15—D20 are laid out to correspond with these analog planes, and our measurements indicate that they generally have the lowest noise of all the analog lines. However, analog performance may vary depending upon the activity of the other GPIOs. Consult the Maple hardware design files for more details.

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 (however, pin D43 is not usable)
• BOARD_NR_PWM_PINS: 15
• boardPWMPins: 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 14, 24, 27, 28
• BOARD_NR_ADC_PINS: 15
• boardADCPins: 0, 1, 2, 3, 10, 11, 12, 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 5 V tolerant.

Errata

This section documents design flaws and other errors.

General

• Barrel jack power supply voltage mistake: The acceptable voltage range given next to the barrel jack on the Maple through Rev 5s manufactured in Spring 2011 is incorrect. The given range is 7V — 18V. In fact, 18V is too high and should not be supplied to your board. The original voltage regulators used on the Maple were rated up to 18V. However, the voltage regulators on current Maple Revs are rated up to only 16V, and due to the current draw requirements of the board, operate properly only up to 12V. The recommended maximum voltage you should apply is 12V, and potentially even lower depending upon the current draw requirements of the application. Please see Power Regulation on the Maple for more information.

• 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 can 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.

• 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.

• PWM marketing mistake: We originally advertised the Maple as having 22 PWM-capable pins; the correct number is 15.

• ADC marketing mistake: We originally advertised the Maple as having 16 analog input pins. Due to the following issue, the correct number is 15.

• ADC on BOARD_LED_PIN: We originally sold the Maple RET6 Edition advertising 16 analog input lines. However, one of them (the one on pin 13) is also connected to the built-in LED. The voltage drop across the LED means that the analog to digital converter on that pin is not really useful. While it is still usable, its readings will be incorrect.

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.

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 (say that three times fast!), 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.

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 Vref 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.

Recommended Reading

STMicro documentation for STM32F103RB 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.
• STM32F103RB overview page with links to further references.

Footnotes

[1]	Revs 2 and 4 were prototypes that didn’t pass internal testing.