B&B Electronics Parallel Port Input/Output Converter PPIO Benutzerhandbuch

 

 

PPIO2899 Manual 

 

15

 

 

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}