B&B Electronics Parallel Port Input/Output Converter PPIO - Manual (Page 27)

PPIO2899 Manual
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25
Input_Byte = inp( Control_Address ) & 0x0F;
if( (Input_Byte & Output_Byte) == Output_Byte )
{
status |= 0x01;
}
}
/* Restore the state of the digital outputs */
Output_Byte = old_value;
outp( Base_Address, Output_Byte );
return (status);
}
This function writes A0h to the upper four digital outputs, then
verifies that the digital output lines are in that state. Then it writes
50h to the upper four digital outputs and verifies that the digital
outputs are in set properly. The lower four digital outputs are
checked in a similar manner with the values 0Ah and 05h.
NOTE: If the PPIO is connected properly and the upper four outputs
(4 - 7) are functional, but the lower four outputs (0 - 3) are not
functional, the parallel port may be in ECP or EPP mode. It must be
in “compatible” or “normal” mode for the PPIO to work properly. The
mode of the parallel port can be changed in the BIOS setup by
pressing either the F2 key or DEL key just after the computer begins
the boot procedure.
For an example of an application that uses these functions, look
at the source code in PPIO.C.