ST20-C1 datasheet(12/205 Pages) STMICROELECTRONICS

12 / 205 page

2.3 Operators used in the definitions

12/205

address map produces the address of the byte at the bottom of the address map.

These operators are represented by the symbols ‘

+’, ‘−’, etc.

Error conditions

Any errors that can occur in instructions which are defined in ter ms of the modulo

operators are indicated explicitly in the instruction description. For example the

add

instruction indicates the cases that can cause overflow or underflow, independently of

the actual addition:

if (sum > MostPos)

{

Areg

′← sum − 2BitsPerWord

Status

′

underflo w ←

clear

Status

′

overflow

← set

}

else if (sum < MostNeg)

{

Areg

′← sum + 2BitsPerWord

Status

′

underflo w ←

set

Status

′

overflow

← clear

}

else

{

Areg

′← sum

Status

′

underflo w ←

clear

Status

′

overflow

← clear

}

...

2.3.1

Functions

Type conversions

The following notation is used to indicate the type cast of x to a 16-bit integer:

int16 (x)

If x is too large or too small to fit into a 16-bit integer then the result of the instruction is

undefined.

Double word splitting

Where a calculation is performed using a 48-bit or 64-bit value, the value may be split

into two words. The function low_word returns the least significant word and the

function high_word returns the most significant word.

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