B&B Electronics PPIO manual Function OutputBit BitNumberBYTE Byte

Notice that in the binary representation of the mask value, line zero’s mask has bit number zero set, and line one’s mask has bit number one set, etc. So, instead of retrieving the mask value from a table, the value is calculated by shifting 00000001b (1 decimal, 01 hexadecimal) right the same number of times as the desired line number. Once the mask value is calculated, it is bitwise ANDed with Input_Byte. If the resulting value is non-zero, the line is ON and a boolean TRUE is returned, otherwise a boolean FALSE is returned.

For example:

Line_Number = 3

Status Register Value = 01010101b

Control Register Value = 10101010b

01010101b (Status Register) AND 11110000b (F0h mask)

01010000b

10101010b (Control Register) AND 00001111b (0Fh mask)

00001010b——> OR 00001010b 01011010b

00000001b (1 decimal)

shift-right 3(Line_Number)= AND 00001000b(bit mask) 00001000b

The function, Output_Bit, returns the status of the selected output line. The function is defined as:

FUNCTION Output_Bit (Bit_Number:BYTE) : BYTE;

BEGIN

If ( ( Output_Byte AND (1 SHL Bit_Number ) ) = 0 THEN

Output_Bit : = 0

ELSE

Output_Bit : = 1;

END; {Output_Bit}

PPIO2899 Manual 15

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