• Introduction
• supported boards
• Building project from sources
• TinyBASIC firwmare installation
• Terminal configuration
• programs examples

STM8 TinyBASIC is a simple programming language but that enable all MCU peripherals configuration and usage on supported NUCLEO boards. Although there is no support for interrupts, TinyBASIC system istself use the following interrupts

• TIMER4 Update that increment an internal milliseconds counter.
• UART(1 or 3) RX full, to queue characters received from terminal.
• I2C to support TinyBASIC I2C.xxxx commands.
• AWU to support TinyBASIC AWU command.
• EXTI4 only on NUCLEO-8S208RB board. That interrupt is triggered by pushing USER button and is used to abort a programm lock in infinite loop.

STM8 TinyBASIC is a simple language for simple microcontrollers projects.

The system is designed to work connected to any PC host whatever the operating system provide a terminal emulator software is available to interface with NUCLEO board. This emulator must support VT100 ANSI sequence as the TinyBASIC system send some of the to host.

This manual explain how to install TinyBasic on supported NUCLEO board and then how to use it to write programs. Aside documention provide by this project the following PDF documents form STMicroelectronics should be consulted as required.

• stm8s20x datasheet
• NUCLEO-8S207K8 user manual
• NUCLEO-8S208RB user manual

Also TinyBASIC reference manual is a must read.

This is an open source project distributed under GPL V3 license.

STM8 TinyBASIC project repository can be found at https://github.com/Picatout/stm8_tbi.

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The NUCLEO boards supported by this project are sold by STMicroelectronics and both use microcontrollerse of ST8S20x family.

These microcontrollers are base on 8 bits MCU which is an extension of the classic MOS6502 cpu. x,Y and SP registers are extended to 16 bits and the PC to 24 bits. The binary code is not compatible with the 6502 and has a lot richer instruction set.

STM8 tinyBASIC use 24 bits integers to give access to flash memory beyond 64KB limit of 16 bits addresses. Both MCU on these boards have flash memory over address 65535.

• NUCLEO-8S207K8 64KB flash meomory in address range 32768..98303
  
  This small board can be plugged on solderless breadboard, but as not access to SPI peripheral on the CN3 or CN4 connectors even though the MCU has one.

• NUCLEO-8S208RB 128KB flash memory in address range 32768..163839
  
  This larger board as more I/Os and SPI peripheral is available on connector CN8.

The BASIC programs can only be saved below 65536 address by design of the BASIC interpreter. Extended memory over that 16 bits limit can be used to store program data.

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• GNU make on Linux system can be installed with:

sudo apt install make

• objcopy from binutils package

sudo apt install binutils

• sdcc also containt sdasstm8. Can be build and installed from source but is also available on Ubuntu.

sudo apt install sdcc 

• stm8flash To flash TinyBasic.bin to NUCLEO board. This tool must be constructed from source but not mandaroy as the binary can be flashed using NUCLEO board virtual drive as described at TinyBASIC firmware installation.

• clone the git on your PC

git clone https://github.com/Picatout/stm8_bit 

• Select the options in config.inc file.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;  configuration parameters 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

DEBUG=0 ; set to 1 to include debugging code 

SEPARATE=0 ; set to 1 for 'make separate' 

WANT_IWDG=0 ; set to 1 to add words IWDGEN and IWDGREF 

; boards list
; set selected board to 1  
NUCLEO_8S208RB=0
; use this to ensure 
; only one is selected 
.if NUCLEO_8S208RB 
NUCLEO_8S207K8=0
.else 
NUCLEO_8S207K8=1
.endif 

; NUCLEO-8S208RB config.
.if NUCLEO_8S208RB 
    .include "inc/stm8s208.inc" 
    .include "inc/nucleo_8s208.inc"
.endif  

; NUCLEO-8S207K8 config. 
.if NUCLEO_8S207K8 
    .include "inc/stm8s207.inc" 
    .include "inc/nucleo_8s207.inc"
.endif 

; all boards includes 

	.include "inc/ascii.inc"
	.include "inc/gen_macros.inc" 
	.include "tbi_macros.inc" 

• DEBUG set to 1 to include debugging code in compiled binary. This code is in debug_support.asm file. To disable this option set it to 0.

• WANT_IWDG Set to 1 to include BASIC commands IWDGEN and IWDGREF in binary. Set to 0 otherwise.

• NUCLEO_8S208RB set to 1 to select this board as target. Otherwise set it to 0 to target NUCLEO_8S207K8 board.

• Use bash script build.sh To build and flash. This script take 2 parameters:

  1. Board type, options are s207 or s208.
  2. Optional parameter flash to flash the binary if build is successful.

~/github/stm8_tbi$ ./build.sh s207 flash

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The repository contain last binary build in project subdirecoty build/stm8s20x.
If there no need to rebuild the project follow these instructions to install the binary on NUCLEO board.

When a NUCLEO board is connected to PC a virtual drive is create

• NOD_8S207 for NUCLEO-8S207K8 board.
• NODE_8S208 for NUCLEO-8S208RB board.

Flashing the TinyBASIC firmware on the board is as easy copying the binary to this drive.

First time I tried to flash one of my NUCLEO-8S208RB board using this method on my Windows laptop it failed. Then I updated the STKLINK firmware and tried again with success.

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The only software required on the PC host to used a NUCLEO board with STM8 TinyBASIC installed is a terminal emulator compatible VT100. This is readily available on Windows and Linux system.

The configuration setup for serial port is:

• 115200 BAUD
• 8 bits
• 1 stop
• no parity

For terminal setup, line termination CR is used.

• On my Ubuntu system I use GTKterm

sudo apt install gtkterm 

but minicom could do as well.

sudo apt install minicom 

On linux system the NUCLEO board virtual serial port name is /dev/ttyACMx where x is a digit idenfying the port.

Here a screen capture of GTKterm configuration window.

If this configuration is saved with default as name will load automatically at GTKterm startup.

Here what is looks like.

• On Windows system I use TeraTerm

Here some screen captures of Teraterm configuration

At startup Teraterm display new connexion dialog box. STMicroelectronics STLink serial port is well idendified.
.
Then terminal configuration must be done. As line terminator, transmit must be CR on receive AUTO or CR can be selected.
VT102 is selected as terminal type.
Line width must be at least 80 characters.

Finally serial configuration is done.

The configuration can be saved but is not restored automatically at startup. When teraterm is restarted

1. the config must be restored from saved file.
2. The new connexion dialog box must be opened and new setting button clicked to make the new setting active.

Finally Tera Term screen capture with font size 12.

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The subdirectory BASIC contains many TinyBASIC programs you can look at for examples.

You should also read STM8 Tiny BASIC language reference manual..

From terminal type WORDS to display all commands,functions and keywords available in the language.

The input case doesn't matter, the system convert to uppercase except for quoted strings.

>words
ABS		ADCON		ADCREAD		ALLOC		AND
ASC		AUTORUN		AWU		BIT		BRES
BSET		BTEST		BTOGL		BUFFER		BYE
CHAIN		CHAR		CONST		CR1		CR2
DATA		DDR		DEC		DIM		DIR
DO		DREAD		DROP		DWRITE		EDIT
EEFREE		EEPROM		END		ERASE		FCPU
FOR		FREE		GET		GOSUB		GOTO
HEX		I2C.CLOSE	I2C.OPEN	I2C.READ	I2C.WRITE
IDR		IF		INPUT		KEY		KEY?
LET		LIST		LOG2		LSHIFT		NEW
NEXT		NOT		ODR		ON		OR
PAD		PAUSE		PEEK		PICK		PINP
PMODE		POKE		POP		POUT		PRINT
PORTA		PORTB		PORTC		PORTD		PORTE
PORTF		PORTG		PORTI		PUSH		PUT
READ		REBOOT		REM		RESTORE		RETURN
RND		RSHIFT		RUN		SAVE		SIZE
SLEEP		STEP		STOP		TICKS		TIMEOUT
TIMER		TO		TONE		TRACE		UBOUND
UFLASH		UNTIL		USR		WAIT		WORDS
WRITE		XOR		
107 words in dictionary

>

NUCLEO-8S208RB board as 4 more command than NUCLEO-8S207K8 board. These commands are for the SPI peripheral.

• Any command list that is not preceded by a line number is compiled an executed immedially.

>for i=1 to 10:? i;:next i
1 2 3 4 5 6 7 8 9 10 
>

• If the first item is a number between 1...32767 the line is consired part of a program and inserted in program space after compilation.

>10 for i=1 to 10:? i;:next i

>list
   10 FOR I = 1 TO 10 : ? I ; : NEXT I 
program address: $91, program size: 25 bytes in RAM memory

>run
1 2 3 4 5 6 7 8 9 10 
>

• If line contains only a line number it is ignore or if an existing line with that number exist it is deleted from the program.

>10

>list

>

• lines can be typed in any order but are inserted in program space in sorted order.

>10 for i=1 to 10:? i;:next i

>5 ' count to 10 

>list
    5 ' count to 10
   10 FOR I = 1 TO 10 : ? I ; : NEXT I 
program address: $91, program size: 43 bytes in RAM memory

>

The 2 boards have 6KB of RAM space but some of it is used by Tiny BASIC system. To know free space available for program type

>? free " bytes free"
5561  bytes free

>

Programs are edited in RAM to reduce flash memory wear but this limit their size to free RAM. To alleviate that limitation an application can span many files. Once a file is tested and debugged it can be save in FLASH memory file system. Using the command CHAIN one file can call another program file for execution. See the command CHAIN in reference manual for more detail.

Both board have a user LED both connected to the same PORTC bit 5 which the sytem configure at bootup as output. In the following example this LED is blinked once/second.
The system define constants for all General Purpose I/O port (PORTx) as well for the 5 registers that control those ports ODR,IDR,DDR,CR1 and CR2. See reference manual for more detail on these.

1 BLINK 
5 ' Blink user LED on board
10 DO BTOGL PORTC , BIT ( 5 ) PAUSE 500 UNTIL KEY? 
20 LET A = KEY ' drop this key from rx queue
30 BRES PORTC , BIT ( 5 ) ' turn off LED 
40 END 

Another way to control this LED is to use DWRITE command.

5 ' CTRL C to quit program
7 ' blink 3 times per second
10 LET B = 1 
20 FOR A = 0 TO 0 STEP 0 ' infinite loop
30 DWRITE 13 , B ' user LED is on D13
40 LET B = 1 - B 
50 PAUSE 333 
60 NEXT A 

In the following example the user LED brightness is controlled by PWM.

    1 PWM.SOFT 
    5 ' Software PWM, control user LED   
    7 GOSUB HELP 
   10 LET R = 511 , S = 1 , N = 0 , P = 0 : ? R ; 
   20 LOOP ' PWM loop 
   22 IF K = P : LET N = N   1 , S = N / 10   1 
   24 IF K <> P : LET S = 1 , N = 0 
   26 LET P = K , K = 0 
   30 IF R : BSET PORTC , BIT ( 5 ) 
   40 FOR A = 0 TO R : NEXT A 
   50 BRES PORTC , BIT ( 5 ) 
   60 FOR A = A TO 1023 : NEXT A 
   70 IF KEY? : LET K = KEY : GOSUB UPPER 
   72 IF ( K = ASC ( \D ) OR K = ASC ( \U ) ) AND K = P : LET N = N   1 , S = N / 10   1 
   74 IF K = 0 OR K <> P : LET S = 1 , N = 0 
   78 IF K = 0 : GOTO 30 
   80 IF K = ASC ( \U ) : GOTO 200 
   84 IF K = ASC ( \F ) : LET R = 1023 : GOTO 600 : '  pleine intensite 
   90 IF K = ASC ( \D ) : GOTO 400 
   94 IF K = ASC ( \O ) : LET R = 0 : GOTO 600 : '  eteindre
   96 IF K = ASC ( \? ) : GOSUB HELP : GOTO 600 
  100 IF K = ASC ( \Q ) : GOSUB CLS : END 
  110 GOTO LOOP 
  200 IF R < 1023 : LET R = R   S : GOTO 600 
  210 GOTO LOOP 
  400 IF R > 0 : LET R = R - S : GOTO 600 
  410 GOTO LOOP 
  600 IF R < 0 : LET R = 0 
  602 IF R > 1023 : LET R = 1023 
  604 GOSUB CLS : ? R ; 
  610 GOTO LOOP 
 1000 UPPER ' upper case letter
 1010 IF K < ASC ( \a ) : RETURN 
 1020 IF K > ASC ( \z ) : RETURN 
 1030 LET K = K - 32 
 1040 RETURN 
 2000 CLS ' clear terminal screen and move cursor home
 2002 ' using ANSI control sequences
 2010 ? CHAR ( 27 ) ; "[2J" ; CHAR ( 27 ) ; "[H" 
 2020 RETURN 
 3000 HELP 
 3010 GOSUB CLS 
 3012 ? "To control LD2 use:" 
 3014 ? , "'D' decrease intensity" 
 3016 ? , "'U' increase intensity" 
 3018 ? , "'F' full intensity" 
 3020 ? , "'O' turn off LD2" 
 3024 ? , "'Q' quit." 
 3026 ? , "'?' help" 
 3028 ? "Press any key to leave this help screen." 
 3030 DO UNTIL KEY? : ? KEY 
 3032 GOSUB CLS 
 3034 RETURN 

The brightness is displayed at top left corner on terminal.

The following terminal keys are used to control brightness

• u to increase
• d to decrease
• f full brightness
• o turn off
• q quit program
• ? display this help

For this example a 10 Kohm potentiometer is connected to analog input A0 and the ADCREAD function is used to read the potentiometer position. Lower leg of potentiometer is connected to GND, upper leg to 3.3V and center one to A0. Rotating the potentiometer varies the LED brightness.

    1 AN.READ
    5 'analog input demo
   10 LET K = 0 :PRINT K;: ADCON  1 
   20 LET R =ADCREAD ( 0 )
   30 IF R :BSET PORTC,BIT(5) 
   40 FOR A = 0 TO R :NEXT A 
   50 BRES PORTC,BIT(5) 
   60 FOR A =A TO  1023 :NEXT A 
   70 IF KEY? :LET K =KEY AND $DF
   80 IF K =ASC (\Q):ADCON  0 :END
   90 PRINT "\b\b\b\b\b\b";R;
  100 GOTO  20 

Q key to quit program.

On line 1 the label AN.READ enable this program to be saved in flash memory as to save a program in the file system its first line must be labeled as this label is used as file name.

>save

>dir     
$B804 206 bytes,AN.READ

>run an.read
$0   
>autorun an.read

>reboot
 AN.READ running
432    
>

• SAVE command to save the program in file system.
• DIR command to display list of saved programs.
  • first number is program address in hexadecimal.
  • second number is program size in decimal.
  • last is file name which is the label on program first line.
• RUN AN.READ run the given file. The file execute from flash this keep RAM free.
• AUTORUN AN.READ Make file AN.READ run at boot up .
• REBOOT command reboot the MCU and the AN.READ is running. AUTORUN \C disable autorun.

TIMER1 is a 16 bits counter with 4 channels that can be configured for input capture or output compare. In this example channel 1 output compare is configured in PWM mode 1 to control brightness of a LED connected to pint D3.

• Cathode -> GND
• Anode -> 100 ohm resistor -> D3

• lower leg 1 -> GND
• center leg 2 (milieu) -> A0
• upper leg 3 -> 3.3V

1. lines 10-40, TIMER1 registers address constants are defined.
2. ligne 60, Enable TIMER1 peripheral clock signal.
3. lignes 80-100, Configure channel 1 in PWM mode 1.
4. ligne 110-120, Configure TIMER1 period for 1023 counts.
5. ligne 130, Adjust duty cycle to 50%.
6. ligne 150, Enable PWM channel 1.
7. ligne 170, enable analog to digital converter.
8. lignes 190-220, Inside DO..UNTIL loop read potientiometer on A0 and set PWM duty cycle with potientiometer value to control LED brightness.
9. Any key pressed on terminal end the program.

1 PWM.HARD 
5 ' pwm on D3 using TIMER1 channel 1
10 CONST TIM1.CR1=$5250,TIM1.ARRH=$5262,TIM1.ARRL=$5263,TIM1.CCMR1=$5258 
20 CONST TIM1.CCR1H=$5265,TIM1.CCR1L=$5266,TIM1.EGR=$5257,TIM1.CCER1=$525C 
30 CONST TIM.CCMR.OCM=4,TIM1.PSCRH=$5260,TIM1.PSCRL=$5261,CLK.PCKENR1=$50C7
40 CONST TIM1.BRK=$526D,TIM1.MOE=7
50 ' Enable TIMER1 clock 
60 BSET CLK.PCKENR1,bit(7) 
70 ' Set up TIMER1 channel 1 for pwm output MODE 1 
80 POKE TIM1.CCMR1, LSHIFT(6,TIM.CCMR.OCM):BSET TIM1.BRK,BIT(TIM1.MOE) 
90 ' no prescale divisor on TIMER clock  
100 POKE TIM1.PSCRH,0:POKE TIM1.PSCRL,0 
110 ' 1023 for counter period, this give 10 bits resolution like the ADC 
120 POKE TIM1.ARRH,3:POKE TIM1.ARRL,255
130 POKE TIM1.CCR1H,1:POKE TIM1.CCR1L,255 
140 ' enable counter 
150 BSET TIM1.CCER1,BIT(0):BSET TIM1.EGR,BIT(0):BSET TIM1.CR1,BIT(0)
160 ' enable analog digital converter 
170 ADCON 1 
180 ' read analog input channel and set TIM1.CCR1 register with value.
190 DO 
200 ? "\b\b\b\b\b";:LET N=ADCREAD(0): ? n;
210 POKE TIM1.CCR1H,N/256:POKE TIM1.CCR1L,N
220 UNTIL KEY? ' quit when a key is pressed 
230 BRES TIM1.CCER1,BIT(0):BRES TIM1.CR1,BIT(0):BRES CLK.PCKENR1,BIT(7)
240 END 

Small servo-motors are controlled by PWM at frequency of 50 hertz. This example show the use of servo command in this purpose. Channel 2 is used and SG90 servo-motor.

The 3 follwing commands are available for servo-motor control purpose.

• SERVO.EN 0|1 0 disable servo control, 1 enable it.
• SERVO.CH.EN ch#,0|1
  • ch# channel number {1..4}
  • 0|1 0 disable that channel, 1 enable it.
• SERVO.POS ch#,usec Set rotation angle of motor.
  • ch# channel number to set.
  • usec pulse width in microseconds {500..2500}

Up to 4 servo can be controlled simultaneously.

WARNING: Don't connect servo-motor power to board 5 volt regulator. Those small motor draw enough current at motor startup to reset the board.

Specification I found for SG90 specify a 1000...2000 usec interval for pulse width. But with this range the rotatation is only 90° So I extended this range to 500...2500 usec to get 180° rotation. One can't always trust datasheet.

1 SERVO.CTRL 
5 ' servo-motor control on channel 1 on D3 
6 ' servo-pulse range 500 usec - 2500 usec.
10 ' enable servo-motor control
20 SERVO.EN 1 ' 0 to disable 
30 'enable channel 1
40 SERVO.CH.EN 1,1 
50 ADCON 1 
60 ' read analog input channel and set TIM1.CCR1 register with value.
70 DO 
80 ? "\b\b\b\b\b";:LET N=ADCREAD(0)*2 500: ? n;
90 SERVO.POS 1,N  ' set servo rotation angle
100 UNTIL KEY? ' quit when a key is pressed 
110 ' disable servo motor control 
120  SERVO.CH.EN 1,0 ' disable channel 0
130  SERVO.EN 0 ' disable TIMER1 
140 END

Note that TIMER1 can't be used for other purpose when it is used for servo control.

I2C is acronym for Inter Integrated Circuit. This is a communication bus used for communication between integrated circuit on same board or assembly. This is a 2 wires bus working in open drain. Up to 128 devices can be connected on 1 bus as each device has a 7 bit address to identify it. In subdirectory BASIC there is 2 demo programs using I2C interface bus.

The commands related to I2C are :

• I2C.OPEN enable I2C bus.
• I2C.CLOSE disable I2C bus.
• I2C.WRITE Send data to device connected on I2C bus.
• I2C.READ Receive data from device on I2C bus.

The program i2c_eeprom.bas demonstrate the usage of I2C interfaced EEPROM 24LC512.

The program i2c_oled.bas demonstrate small I2C interfaced OLED grahpic display.

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