Maple — Maple v0.0.11 Documentation

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# Maple

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

Contents

- 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
  - Low-Noise ADC Pins
- Board-Specific Values
- Hardware Design Files
- Failure Modes
- Errata
  - General
  - By Rev
    - Rev 5
    - Rev 3
    - Rev 1
- Recommended Reading

## 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 (GPIO)
- 15 PWM pins at 16 bit resolution (PWM)
- 15 analog input pins, 12-bit ADC resolution (ADC)
- 2 SPI peripherals (SPI)
- 2 I2C peripherals (I2C)
- 7 Channels of Direct Memory Access (DMA) (dma.h)
- 3 USART peripherals (USART)
- One advanced and three general-purpose timers (Timers)
- Dedicated USB port for programming and communications (USB)
- JTAG (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
- 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.

Warning

Silkscreens on Maples up through Rev 5s manufactured in Spring 2011 falsely indicated that the barrel jack could be supplied by up to 18 V. We recommend a barrel jack input voltage no greater than 12 V.

See this erratum for more information.

## 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` 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.

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

### 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, 42
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, 39
EXTI14 | 22, 33, 40
EXTI15 | 23, 34, 41

### USART Pin Map

The Maple has three serial ports (also known as 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

### 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 7 V — 18 V. In fact, 18 V is too high and should not be supplied to your board. The recommended maximum voltage you should apply is 12 V.

  The original voltage regulators used on the Maple were rated up to 18 V. However, the voltage regulators on current Maple Revs are rated up to 16 V. Our tests indicate that they operate correctly through 12 V. We do not recommend higher input voltages.

- 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, 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); general, definitive resource for 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.

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