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Serial Terminal: Hardware

Mecrisp Stellaris is programmed via a serial terminal, often running on a PC. Default communication parameters are serial, at 115200 baud, 8N1 and use the on MCU USART.

USB-3.3v Dongle or cables

USB serial Dongles or cables are usually the easiest way to connect a PC running Picocom to a STM32 Discovery Board. Don’t forget to buy at least four female to female pin connecting cables for a dongle. These are usually available online in bundles.

Unix friendly CP2102 chipset dongle, with Rx, Tx, nRTS,nCTS and other control signals, including +5 and +3.3 volts available on pins or holes for pins or wires to be soldered. Usually under $2 on eBay, and the most useful model in my opinion


Unix friendly PL2303 chipset dongle, with Rx, Tx, 3.3v, 5v available on pins at the rear, but no control signals, unless you want to hand solder fine wires to the SMT chip. Usually about $0.70 AUD each in a pack of 5 on Ebay


USB-3.3v cable. The cable length and flying leads make this a handy unit. About $25 on eBay

_images/usb-3_3V-cable.jpg _images/cbl-usb-rs232-3.3v.jpg
signal color
+5v Red
Ground Black
TX Orange (output)
RX Yellow (input)
nCTS Brown (input)
nRTS Green (output)


Don’t use RS-232 cables or you may blow up your Board/MCU from overvoltage

Serial Pin Connection Table For Various Boards

Mecrisp-Stellaris default serial pin connections. These can be usually be changed in the Mecrisp-Stellaris assembly source code without too much effort.
Board MCU Type TX RX MCU USB Available ? Notes
Stellaris Launchpad LM4F120 UART 0 ? ? Y  
Chinese QF-LM4F232 LM4F232H5QC ? ? ? ?  
Tiva Connected Launchpad TM4C1294 USB na na Y Use connector U22
TI MSP432 Launchpad MSP432P401R USCI 0 P1.3 P1.2 Y  
LPC1114FBD48 LPC1114FBD48 UART P1.7 P1.6    
LPC1114FN28 LPC1114FN28 UART P1.7 P1.6 N  
LPC1115FBD48 LPC1115FBD48 UART P1.7 P1.6 N  
STM32F030F4 STM32F030F4 USART1 PA9 PA10 N  
STM32F030K6 STM32F030K6 USART1 PA9 PA10 N  
STM32F0 Discovery STM32F051R8 USART1 PA9 PA10 N  
STM L053 Discovery STM32L053C8 USART1 PA9 PA10 N  
STM VL Discovery STM32F100RB USART1 PA9 PA10 N  
Blue Pill STM32F103C8T6 USART1 PA9 PA10 Y  
Shenzhen LC mini STM32 STM32F103C8T6 USART1 PA9 PA10 Y  
STM Nucleo L152RE STM32L152RE USART2 PA9 PA10 Y  
STM F3 Discovery STM32F303VCT6 USART1 PA9 PA10 N  
STM Nucleo 401RE STM32F401RE USART2 PA2 PA3 Y  
STM F429 Discovery STM32F429ZIT6 USART1 PA9 PA10 N  
STM F4 Discovery STM32F407VGT6 USART2 PA2 PA3 N  
STM Nucleo 411RE STM32F411RET6 USART2 PA2 PA3 Y  
STM L476 Discovery STM32L476VG USART2 PD5 PD6 Y  
STM F746 Discovery STM32F746NG ? ? ? ?  
Freescale Freedom FRDM?KL25Z KL25Z128VLK4 UART0 ? ? Y  
KL46Z256 KL46Z256 UART0 ? ? Y  
Teensy 3.1 MK20DX256VLH7 UART0 Pin3 Pin2 ? Pin18/19 CTS/RTS
nRFgo Starter Kit nRF51822 ? ? ? ?  
nRF52832 nRF52832 UARTE P02 P03 ?  
NUC123 NUC123 UART0 ? ? ? 64pin and 48pin only
Infineon XMC2GO XMC1100Q024F0064 ? ? ? ?  
EFM32 Giant Gecko EFM32GG990F1024 ? ? ? ?  


See your mecrisp-stellaris-x.x.x/README for how to Flash your chip.

Note: Direct MCU USB access

Some MCU’s offer on chip USB peripherals for which Mecrisp-Sterllaris has limited support (see the list above).

Compared to using a direct MCU USB connection, using the MCU USART and a USB/3.3volt dongle may initially seem redundant but Forth project development involves regular resetting/rebooting of the MCU (as one screws up the hardware configs).


Resetting the MCU kills the USB peripheral which causes the USB device to be lost at the PC level with the subsequent death of the PC terminal application.


With a USB/3.3volt dongle, you can reset the MCU as much as you like and your terminal application will stay blissfully ignorant and happy. You still have the convenience of USB with a USB/3.3volt dongle.

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