PROGRAMMABLE LOGIC CONTROLLER
with embedded BASIC interpreter

CONTENTS

1. INTRODUCTION
2. AVR BASINT, COMMANDS & FUNCTIONS
2.1 INPUT/OUTPUT CONSOLE
2.2 PROGRAM CONTROL
2.3 DATA
2.4 INTERRUPTS AND OPCODE SUPPORT
2.5 DEFINE AND USE CONTROLLER¡¯S PINS
2.6 INTERNAL RESOURCE ACCESS
2.6.1 16-bit registers access
2.7 MATH ROUTINES
2.8 SOME BASIC EXTENTIONS
2.9 TWO WIRE INTERFACE
2.10 DIAGNOSTIC
3. PRE-PROCESSOR
4. PROGRAM DOWNLOADING

1. INTRODUCTION

Controller with embedded Basic interpreter (PLC-BASINT) is a compact device that can operate as a PLC (program logic controller) for home automation, control, etc. For example, this one can dial-up by modem to the remote computer and send the status of the controlled system, can control some processes, temperature regulation, battery charging, can be used for educations and hobby purposes.

PLC-BASINT has analogue and discrete input/output and an RS232 interface to communicate with other devices and to reflash a control program. The control program is a text version of BASIC language. The main task of the controller is to interpret BASIC commands. The TBC version of the BASIC language has commands to operate with discrete I/O, ADC and PWM. The view of controller PCB is shown below in the figure 1.

Figure 1

The main feature of this controller is that users do not need any special hardware and software tools. For program writing they can use any text editor, NotePad for example. HyperTerminal is enough for program downloading. Both of these programs are standard MS Windows applications. The interpreter BASINT converts the user Basic program to the internal format at the download stage. That allows reduce program size and get fast speed interpreting.

Technical details:

Schematic in PDF format

Controller external connections:

Figure 2

4. PROGRAM DOWNLOADING

HyperTerminal or another terminal application must be set up as shown below:

Baud rate 57600 bps
Data/Stop bits 8/1
Parity None
Flow Control Hardware
Terminal emulation ANSII / VT100
Add sent CR with LF

Figure 3

There are two ways to download.
The first one is by using the text file sending option of the terminal.
The second way is downloading using paste from the clipboard if you are using Windows HyperTerminal, for example.

1.Make sure that write protect jumper is open.
2.Connect the controller to PC by RS232 cable.
3.Power it up.
4.Start terminal application.
5.Press the reset button on the controller.
The start page appears in the terminal window.
6. Press menu option 2 to force the controller be waiting for input text.
7. Send a program by using the text file sending option of the terminal or paste text from the clipboard.
8. Press menu option 1 to list the downloaded program.
9. Press menu option 3 to run the downloaded program.
10. Close write protect jumper. It alows:

- protect program;
- diasable start page screen;
- automatically sart program when the controller is powered up.

This is starting page on HyperTerminal with controller connected to PC serial port.

Figure 4

2. AVR BASINT. COMMANDS AND FUNCTIONS

There are some features of BASINT. - Program lines don¡¯t have numbers. Line numbers are using only for label¡¯s mark.
Numbers:
All numbers are the signed integers in a range from -32767 up to +32767.
There are three forms of numbers representation:

- Decimal;
- Hexadecimal, numbers have a prefix &H;
- Binary, numbers have a prefix &B;

Variables:
There are 26 variables denoted by the letters A through Z. These are represented internally as 16-bit, two's-complement integers.
There are up to 26 one-dimensional arrays. Size of arrays must be defined before using. Maximum size depends of current free memory. The array elements are accessible by an index in the parentheses. For example: A(0), B(18). Note that A an A(n) are the different variables.

Operators
Arithmetic:

+ addition
- subtraction.
* multiply
/ integer division (note that 14/5 = 2
MOD - remainder from division (14 MOD 5 = 4).
AND – bit-wise logical AND (3 AND 6 = 2)
OR – bit-wise logical OR
XOR – bit-wise logical XOR

Compare:(using only with operator IF):
= equal
<> (or ><) not equal
> more
< less
>= (=>) more or equal
<= (=<) less or equal

Expressions:
Expressions are formed with numbers and variables with arithmetic operators between them. Operators of comparison cannot be used in expressions. Parentheses can be used to alter the order of evaluation.
Labels:
Label is a number from 0 to 32767. Labels must be set before line that is a point to jump or is a start line of subroutine. It is not recommended to number all of the lines the labels table is limited up to 64 labels.

2.1 CONSOLE INPUT/OUTPUT

Action:
Clears the screen and move cursor to top left corner
Syntax:
CLS

Action:
Prints the message on the console
Syntax:
PRINT [output list]

The elements of the output list can be separated by semicolon that allows output more than one variables or strings at one line without spaces between the elements. Semicolon at the end of the line cancels adding CR and LF.
The elements of the output list can be separated by comma that inserts number of spaces to set output to the next position of tabulation. Comma at the end of the line cancels adding CR and LF.

Examples:

Action:
Sets the position of the printing symbol for PRINT operator
Syntax:
PRINT AT(x,y);[list]
x – row position (from 1 to 80)
y – column position (from 1 to 24)
Example:

Action:
Sends symbol to the console by its code that is result of expression. Using with PRINT operator
Syntax::
PRINT [list1; or ,] CHR(val)[; or , [list2]]
val – symbol code from 0 to 255. All another integer values will be got as a low byte of word
Example:

Action:
HEX – puts to the console a value in hexadecimal form,
BCD - puts to the console a value in BCD form,
BIN - puts to the console a value in BIN form.
Functions HEX, BCD, BIN are the elements of output list for PRINT operator.
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PRINT [list1; or ,] HEX(value, digits)[; or , [list2]]
PRINT [list1; or ,] BCD(value, digits)[; or , [list2]]
PRINT [list1; or ,] BIN(value, digits)[; or , [list2]]

value – value or expression
digits – number of printed digits

Example:

Action:
Sets the console output attributes
Syntax:
ATTR  expression

An expression defines output attributes:

0 – standard brightness
1 – more light brightness
4 – underscore
5 – blinking
7 – color inverting
8 – set color of symbol and background the same

Action:
Sets color attributes for console output
INK – sets the symbol color
PAPER – sets the background color
Syntax:
INK  expession
PAPER  expession

An expession defines the color

0 – black
1 – red
2 – green
3 – yellow
4 – blue
5 – magenta
6 – cyan
7 – white

Note. Using AT, CLS, ATTR, PAPER, INK allows change attributes on ANSI terminal, as console. Most terminals program can support this mode.

Action:
Waits for input value. Puts value to the variable after receiving CR
Syntax:
INPUT ["Invite msg",] variable
Examples:

Action:
Checks console buffer for the received symbols. Return –1 if empty and symbol¡¯s code if not.
Syntax:
Variable = INKEY()
Examples:

Action:
Is waiting for a single symbol. Returns the code of received symbol.
Syntax:
Variable = WAITKEY()
Examples:

2.2 PROCESS CONTROL OPERATORS

Action:
Condition branch operator
Should be written in one line only.
Syntax:
IF condition THEN operator1 [ELSE operator2]
Examples:

Action:
Loop operator
Syntax:
FOR Variable = expression1 T¬° expression 2
some repeating actions
NEXT
Note. Step = 1 always
Examples:

Action:
Unconditional branch
Syntax:
GOTO label
Example:

Action:
Calls subroutine
Syntax:
GOSUB label
Example:

Action:
Returns from subrouting
Syntax:
RETURN
Example:

Action:
Finishes the program execution
Syntax:
END
Examples:

Action:
Stops the program execution, clears receiving buffer, starts after getting new symbol in the input buffer
Syntax:
STOP
Examples:

 Action:
Comments line. Interpreter skips the rest of code in this line.
Syntax:
REM [any string]
operator : REM [any string]
Examples:

Action:
Forms delay 1..65535 mSec
Syntax:
DELAY expression
Examples:

2.3 DATA

Action:
Defines an array size
Syntax:
DIM list
Note:
Maximum size of array depends of available memory and controller type

        
Examples:

Action:
Specifies constant values to be read by READ operator. Note that max length of data line cannot be more than 64 symbols per 1 line. Max lines of data limited only of available flash memory.

Syntax:
DATA list
Pointer sets to begin of first data block when program starts
Examples:

Action:
Reads DATA and moves pointer to next point
Syntax:
READ list
Example:

 Action:
Allows read the DATA block more than one time. Sets the pointer at the needed labeled block of data.
Syntax:
RESTORE [label]
RESTORE without parameters sets pointer to begin of the first data block.
Examples:

Action:
Writes byte to the address in EEPROM
Syntax:
WRITEEEPROM address, byte

Action:
Reads byte from the address in EEPROM
Syntax:
Variable = READEEPROM(address)

2.4 INTERRUTS and MACHINE CODE

 Action:
Enables interrupts
Syntax:
ENABLE

 Action:
Disables interrupts
Syntax:
DISABLE

 Action:
Creates block of machine code on program downloading stage. A few lines of INLINE in any place of program create consequtive block of a code in special area of memory. If the block of a code is formed by several lines INLINE, it is necessary to take care, that interpreter will look only on first of them. The rest of INLINEs should be hidden after operators RETURN or GOTO
The block of a code should be issued as the subroutine, last operator should be operator RET.
Communication with BASIC variables is simple, registers R16, R17 contain the pointer to variable A. A principle of formation of the address of any of 26 (from A up to Z) scalar variables following:
Address = value of R16R17 + 2 * (symbol code - 65)

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  INLINE opcode1, opcode2¡¦.
Example:

Note. It is possible to automate process of creating INLINE blocks. Just use bin2line.exe to convert machine code to INLINE operators.
It is shown below:

avrasm32 -fI -l %1.lst -o %1.hex %1.asm
hex2bin %1.hex %1.bin
bin2line -i %1.bin -o %1.bas

.include "m64def.inc"
mov r30,r16
mov r31,r17
ld  r18,z+
ld  r19,z+
cli 
out OCR1AH,R19
out OCR1AL,R18
sei
ret

INLINE block after conversion:

INLINE 12256,12273,37153,37169,38136,48443
INLINE 48426,38008,38152

You need put it in BASIC program, add label before the first INLINE and write RETURN or GOTO (as you need) after the first INLINE

200   INLINE 12256,12273,37153,37169,38136,48443
RETURN
INLINE 48426,38008,38152

Action:
Creates the block of a machine code at a stage of program loading.
Connects a code to a vector at a stage of execution.
If code of interrupt handler does not fit in one line, it is possible to continue in next line, but using INLINE operator. The line with INTERRUPT should be separated from other code by one of operators RETURN, GOTO as you need. At a stage of execution the line with INTERRUPT should be interpreted once for interrupti initialization. Requirements on registration of the block of a code same as well as for operator INLINE. Can be simultaneously used up to 10 vectors. It is impossible to set interruptions For UART0 and TIMER0 as they are used by system.
Syntax:
INTERRUPT vector, opcode1, opcode2¡¦.
Example:

Action:
Disconnects the a handler code from vector and disables corresponding interrupt.
Syntax:
DELETEVECTOR vector

 Action:
Assigns value of variable used in interrupt subroutine. During this action interpreter disables interrupts to provide complete (atomic) updating a two-byte variable. It is necessary, as operation of giving contains a chain of several commands which could be broken off by the interrupt, providing access to the same variable..
Syntax:
PUTATOMIC var, value

Action:
Gets value from a variable used in an interrupt. During this operator executing interrupts are disabled.
Syntax:
some_var = GETATOMIC(var)

2.5 CONTROLER¡¯S PINS ASSIGNMENT AND USE

Action:
Defines the pin function of the controller pins.
The controller pins have numbering from zero up to some maximum value that depends on the type of controller. The Sets of additional pin functions depends on type of the controller too. See table to reference.

Syntax:
DEFPIN pin AS type

Note.

Example:

Action:
Sets pin logic level to zero
Syntax:
CLEARBIT pin

Action:
Sets pin logic level to one
Syntax:
SETBIT pin

Action:
Switches pin logic level to the inverted state
Syntax:
TOGGLE pin

Action:
Reads pins logic level
Syntax:
var = TESTPIN(pin)

Action:
Puts a digital value out to the PWR channel
Syntax:
PWR pwm_pin, value

Action:
Set the analog multiplexer up
Syntax:
SETADMUX value
Note.
value = reference source + channel number

Action:
Reads meassured value from the current channel ADC
Syntax:
var = AD¬³

2.6 ACCESS TO INTERNAL RESOURCE OF MICROCONTROLLER

Action:
Writes byte to memory or I/O port
Syntax:
POKE adr, val

Action:
Reads byte from memory or I/O port
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var = PEEK(adr)

Note: You should reference to avr datasheet to get the address of register. Remember there are two addresses: I/O and memory. PEEK and POKE operate with memory address and and you need to add 32 to get I/O address.

2.6.1 Access to the 16-bit registers

Access to the 16-bit registers of avr micro has features. It uses hardware temporary 8-bit register. From the program point of view, there are some rules to access:
1. Use IN and OUT assembler operators.
2. For write: access to the highest register is first.
3. For read: access to the lowest register is first.

This is an example of two subroutines for access register OCR1A using BASIC variable A:

REM .include "m64def.inc"
REM    mov r30,r16
REM    mov r31,r17
REM    ld  r18,z+
REM    ld  r19,z+
REM    cli 
REM    out OCR1AH,R19
REM    out OCR1AL,R18
REM    sei
REM    ret

REM   WRITE to OCR1A
200   INLINE 12256,12273,37153,37169,38136,48443
RETURN
INLINE 48426,38008,38152

REM  .include "m64def.inc"
REM    mov r30,r16
REM    mov r31,r17
REM    cli 
REM    in R18,OCR1AL
REM    in R19,OCR1AH
REM    sei
REM    st  z+, r18
REM    st  z+, r19
REM    ret

REM   READ from OCR1A
300   INLINE 12256,12273,38136,46378,46395,38008
RETURN
INLINE 37665,37681,38152

2.7 MATH ROUTINES

Action:
Returns high byte
Syntax:
var = HIGH(expression)

Action:
Returns low byte
Syntax:
variable = LOW(expression)

Action:
Returns absolute value
Syntax:
variable = ABS(expression)

Action:
Shifts value of variable left. The LSB is set to 0.
Syntax:
ROL variable, number of shifts

Action:
Shifts value of variable right. The MSB is set to 0.
Syntax:
ROR variable, number of shifts

Action:
Performs the scaling
Syntax:
SCALE Variable, multiplier, divider
Examples:

2.8 SOME BASIC EXTENTIONS

Action:
Returns pulse width on the controller pin unit that are approximately 1 uS at frequency of quartz 14.745 MHz
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var = PULSEIN(pin, option, timeout)
Note

Action:
Forms pulse on the pin
Syntax:
PULSEOUT pin, duration

pin – pin number
duration - duration in uSec for resonator 14.745 MHz

Action:
Returns the incoming sequence of bits
Syntax:
var = SHIFTIN(data_pin, clock_pin, bits, delay, option, timeout)
Note:

Action:
Outputs contents of a variable as sequence of bits
Syntax:
SHIFTOUT var, data_pin, clock_pin, bits, delay, option
Note:

2.9 TWO WIRE INTERFACE

Action:
Iinitializes TWI (I2C)
Syntax:
TWIINIT bps, prescale

bps – number for bps needed
prescale - can be defined from equation:

SCL frequency = CPU Clock frequency / (16 + 2(bps) * 4^prescale)

Action:
Generates START condition on SDA and SCL pins
Syntax:
TWISTART

Action:
Sends byte to TWI (I2C) device
Syntax:
TWIWRITE ¬Ò¬Ñ¬Û¬ä

Action:
Reads byte from TWI (I2C) device. ACK/NACK generate
Syntax::
var = TWIREAD(ack)
Parameter ack:
0 – NACK
1 – ACK

Action:
Generates STOP condition on SDA and SCL pins
Syntax::
TWISTOP

 Example:

2.10 DIAGNOSTICS

At execution of the program there can be situations at which the interpreter stops the work and sends the message on an error in which the code and number of a line is underlined.

Action:
Returns last error or critical situation code
Syntax:
var = LASTERROR()
Note::

3. PRE-PROCESSOR

BASIC language is an extremely simple language, but it is difficult to write big programs by BASIC because the variables length is too short. The best case is when the possible length allows to write ¡°selfcomment¡± variables. But, long variables, labels could be the cause of slow speed interpreting and resource consuming. A special program-converter can help to resolve this coflict. Our interpreter will still working with short names, but we will work with long names by placing the lines with the preprocessor instruction DEFINE in the program text as shown below:

DEFINE some_long_name = D ¡® defines self comment variable
DEFINE one_more_long_name = 100 ¡® defines constant or label

You can use the apostrophes to start a comment line. At the end you will get something like the program shown below:

This text needs to be cnvereted before downloading into controller. First we save text of program as shift.bas for example . Then in a command line we can type:
BASPREP.EXE –I shift.bas –O shift.out

Note. BASPREP.EXE must be placed in the same catalogue or be visible of a current arrangement. You can put to C:WINDOWS for example.

We will get something like shown below as a result of conversion.

The preprocessor eliminates all of the comments and substitute the long names for theirs short values.