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

• 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 (GPIOs)
• 18 PWM pins at 16 bit resolution
• 15 analog input (ADC) pins at 12 bit resolution
• Built-in, 2 channel DAC at 12 bit resolution (dac.h).
• 2 SPI peripherals with I2S support
• 2 I2C peripherals
• 12 Channels of Direct Memory Access (DMA) (dma.h) with 2 DMA controllers
• 3 USART (serial port) peripherals
• 2 advanced, 4 general-purpose, and 2 basic 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 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 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 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.

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, 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 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.

Recommended Reading

STMicro documentation for STM32F103RE microcontroller:

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