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Programmers Memory Reference

Variable space in RAM

W 0 W 1 W 2 W 3 W 4 W 5 W 6
B 0 B 1 B 2 B 3 B 4 B 5 B 6 B 7 B 8 B 9 B 10 B 11 B 12 B 13
                           

B0 to B13 are Byte variables (8 bits), and W0 to W6 are Word variables (16 bits).

The RAM available to the programmer of the '08 is 14 Bytes, or 7 Words, or a combination of these. Note that the Word variables and the Byte variables are overlaid, so writing a word to, say, W 4, results in variable B 8 & B 9 being occupied by the upper and lower bytes of the Word variable.

Also, the first Word (W0) is accessable as 16 bits of bit-memory, with the first Byte (B0) split into the first 8 Bits (BIT0, BIT1, BIT2, BIT3, BIT4, BIT5, BIT6, BIT7) and the next Byte (B1) split into the final 8 bits (BIT8 to BIT15).
W0
B0 B1
BIT7 BIT6 BIT5 BIT4 BIT3 BIT2 BIT1 BIT0 BIT15 BIT14 BIT13 BIT12 BIT11 BIT10 BIT9 BIT8

the use of the keyword symbol is a good idea...


Example code:

Let b0 = 3          'assigns the value of 3 to the variable b0  
Let b0 = b0 + 1 'adds 1 to the value stored in b0
debug b0 'shows the value of the variables
The above code sample makes the variable b0 have the value of 3, then adds 1 to it. The debug output window will show all the variables, and that the value stored in b0 is 4.

Now lets show a few more things...
        Let b0 = 0          'assigns the value of 0 to the variable b0  

repeat: 'this is a label that 'bookmarks' this spot in the program
Let b0 = b0 + 1 'adds 1 to the value stored in b0
debug b0 'shows the value of the variables
pause 1000 'pause for 1 second (1000 milliseconds)
goto repeat 'this jumps to the label called repeat
In this example we assign a value of 0 to the variable b0, then repeatedly add 1 to it, displaying the results then pausing a second before repeating everything except the first line.


Interrupts

The Picaxe can nest interrupts up to 4 deep.
Map of RAM allocation and access in Picaxe
 
 

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