Parallel port

 
Each SPP has three registers accessible via three successive ports :

the base address or data register      &H3BC   &H378   &H278   W (R)
the control register      &H3BD   &H379   &H279    R
the command register      &H3BE   &H37A   &H27A    W

SPP 1 Base Address is written in memory adress 0000:0400 on two bytes
SPP 2 Base Address is written in memory adress 0000:0402 on two bytes
SPP 3 Base Address is written in memory adress 0000:0404 on two bytes
SPP 4 Base Address is written in memory adress 0000:0406 on two bytes

If SPP x is not hardware implemented, the memory address is 0

ON A DB25 : - datas b0 to b7 are respectivly on pins 2 to 9
             - control pins 10, 11, 12, 13, 15 (some are inverted :)
             - commands pins 1, 14, 16, 17   (some are inverted :)

If port &H378 exists on your computer then

DefInt A
' will set all the data lines of PP to 5 Volts (logical 1)
Out &378, 255
' will set all the data lines of PP to 0 Volts (logical 0)
Out &378, 0
' will read what was last written on PP (it cannot read anythng
' else than its output ! It is not an input port. For that see EPP
A = Inp (&H378)
' Will read the 5 existing bit of the control register
A = Inp (&H379)

Reading or writing a port takes on ANY computer something like
1.5 microseconds, this can be usefull if you need very short
temporisation (IE : reading the keybord buffer with A = Inp (&h60)
It's harmless)