Maple

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″

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.

Maple Rev 5

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.

Maple Rev 3

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.

Maple Rev 1

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 D39D42) 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 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.

  • 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.