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 (the STM32F103RET6, hence the name) than the one on the base Maple (the STM32F103RBT6) in the hands of Maple developers.

Technical Specifications

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 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 RET6

Power regulation on the Maple RET6 works in the same way as the standard Maple.

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 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 D39D42 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.

Note that this table is not exhaustive; on some pins, more peripherals are available than are listed here.

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

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. 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 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, D24, D38
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 RET6 Edition has three serial ports whose pins are broken out to headers (also known as USARTs). 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

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 acceptable voltage range given next to the barrel jack on the Maple RET6 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.
  • 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 the standard libmaple DAC interface) 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.