Maple RET6 Edition — Maple v0.0.11 Documentation

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# Maple RET6 Edition

This page is a general resource for information specific to the Maple RET6 Edition. The Maple RET6 Edition is a “beta” board released as a simple way to get a more powerful chip than the one on the base Maple (the STM32F103RET6, hence the name) in the hands of Maple developers.

Contents

- Technical Specifications
- Powering the Maple RET6 Edition
- 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
- Recommended Reading

## Technical Specifications

- MCU: STM32F103RET6, a 32-bit ARM Cortex M3 microprocessor
- Clock Speed: 72 MHz
- 512 KB Flash and 64 KB SRAM
- 43 Digital I/O Pins (GPIO)
- 18 PWM pins at 16 bit resolution (PWM)
- 15 analog input pins, 12 bit ADC resolution (ADC)
- Built-in, 2 channel DAC at 12 bit resolution (dac.h).
- 2 SPI peripherals with I2S support (SPI)
- 2 I2C peripherals (I2C)
- 12 Channels of Direct Memory Access (DMA) (dma.h) with 2 DMA controllers
- 3 USART devices (USART)
- 2 advanced, 4 general-purpose, and 2 basic 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 are 2.05″ × 2.1″

## Powering the Maple RET6 Edition

The Maple RET6 Edition is powered in the same way as the standard Maple.

Warning

The RET6 Edition silkscreen falsely indicates that the barrel jack accepts 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

The RET6 Edition has 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 RET6 Edition 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 RET6 Edition’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/USART | 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

3_MOSI

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

5_RX

Yes

D26

PC10

4_TX

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

1_BKIN

2_SMBA

3_CK

2_NSS

Yes

D32

PB13

1_CH1N

3_CTS

2_SCK

Yes

D33

PB14

1_CH2N

3_RTS

2_MISO

Yes

D34

PB15

1_CH3N

2_MOSI

Yes

D35

PC6

8_CH1

Yes

D36

PC7

8_CH2

Yes

D37

PC8

8_CH3

Yes

D38

PC9

8_CH4

Yes

D39

PA13

Yes

D40

PA14

Yes

D41

PA15

3_NSS

Yes

D42

PB3

3_SCK

Yes

### Timer Pin Map

The following table shows what pins are associated with a particular timer’s capture/compare channels. Note that timer 5’s channels share pins with timer 2 (e.g., timer 5 channel 1 is also available on D2, channel 2 on D3, etc.).

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
8 | D35 | D36 | D37 | D38

### EXTI Line Pin Map

The following table shows which pins connect to which EXTI lines on the Maple RET6 Edition.

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 RET6 Edition has three serial ports whose pins are broken out to headers (also known as USARTs). 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

Unfortunately, UART4 and UART5 aren’t completely available.

### 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. More details in the Maple hardware documentation.

## Board-Specific Values

This section lists the Maple RET6 Edition’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`: 18
- `boardPWMPins`: 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 14, 24, 27, 28, 35, 36, 37
- `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 (unfortunately, due to the Maple Rev 5 design, UARTs 4 and 5 have pins which are not broken out).
- `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 (unfortunately, due to the Maple Rev 5 design, SPI3 is unavailable).
- `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. Other than the processor used, the design files for the Maple RET6 edition are identical to the Maple Rev 5, which are in the `maple-r5` subdirectory of the Maple repository. 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 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 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

This section lists known issues and warnings for the Maple RET6 Edition. Some of these are simply due to the RET6 Edition using the Maple’s circuit board, which was not designed to accomodate extra features only available on the STM32F103RET6.

- Barrel jack power supply voltage mistake: The silkscreen next to the barrel jack connector incorrectly indicates that up to an 18 V input voltage is allowed. We do not recommend exceeding 12 V.

  See this Maple erratum for more information.

- Power supply marketing mistake: We originally sold the Maple RET6 Edition advertising that it was capable of supplying up to 800 mA; the correct value is 500 mA.

- UART4, UART5 GPIOs unavailable: Pins related to UARTs 4 and 5 are not broken out to headers (specifically, PC11/UART4_RX and PC12/UART5_TX). This is due to the RET6 Edition’s board layout being that of the Maple Rev 5, which was not designed with these RET6-specific features in mind.

- DAC channel 2 on BOARD_LED_PIN: The Maple Rev 5 connects PA5 to the board’s built-in LED; this is the same GPIO bit which is connected to the DAC’s channel 2 output. This is also due to the RET6 Edition’s board layout being that of the Maple Rev 5. The DAC output channel is still available, and (if you use libmaple) its output is buffered by default, so this may not significantly interfere with its functionality.

- Reset and PB4 tied together: The RET6 Edition’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. Also, since PB4 is SPI3_MISO, the SPI3 peripheral is not fully usable.

- SDIO lines not broken out: The RET6 Edition’s SDIO peripheral is not usable, as some of its data lines are either not broken out or used for other purposes. This is also due to the RET6 Edition’s board layout being that of the Maple Rev 5.

- 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.

## Recommended Reading

STMicro documentation for STM32F103RE microcontroller:

- Datasheet (PDF); covers STM32F103xC, STM32F103xD, STM32F103xE.
- Reference Manual RM0008 (PDF); general, definitive resource for STM32F1 line.
- Programming Manual PM0056 (PDF); assembly language and register reference.
- STM32F103RE overview page with links to further references.

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