B&B Electronics Parallel Port Input/Output Converter PPIO - Manual (Page 21)

PPIO2899 Manual
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19
The function, Set_IRQ_OFF(), tells the parallel port not to
generate any interrupts. This should be called immediately after
Set_Start(). It is defined as:
void Set_IRQ_Off(void)
{
outport (Control_Address, 0x04);
}
The function, In_Byte(), returns the value of the variable,
Input_Byte. It is defined as:
unsigned int In_Byte(void)
{
return (Input_Byte);
}
Notice that this does not read the value of the parallel port. The
function Read_Input_Bit() reads the port.
The function, Out_Byte(), returns the value of the variable
Output_Byte. It is defined as:
unsigned int Out_Byte(void)
{
return (Output_Byte);
}
Notice that this does not read the parallel port, it only returns the
value of Output_Byte.
The function, Read_Input_Bit(), returns the status of the
specified input line. The function is defined as:
boolean Read_Input_Bit(unsigned char Line_Number)
{
Input_Byte = (inport(Status_Address) & 0xF0) |
(inport(Control_Address) & 0x0F);
return ( ((Input_Byte & (1 << Line_Number)) != 0) );
}