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

 

 

PPIO2899 Manual 

 

3

 

To understand how the PPIO can be controlled you  must 

first understand how the parallel port works inside the computer. The 
parallel port is designed to connect the computer with the outside 
world. It can have up to 12 TTL compatible outputs and up to 9 TTL 
compatible inputs. It cannot have both at the same time since some 
inputs and outputs share pins. Eight of the outputs and five of the 
inputs are dedicated. Four of the lines can be either inputs or 
outputs. 
 

 

 

The main use for the parallel port is to send data to a 

printer. The port uses the eight dedicated outputs for data and the 
other lines for handshakes. Under normal printer operation, the 
computer will put an eight-bit byte on the eight lines (pins 2-9) and 
then use the Strobe output (pin 1) to tell the printer to read the data. 
Upon receipt of an Acknowledge (pin 10) from the printer the 
computer knows that the eight bit word was received. It can then 
send the next word. Other lines are used for busy, off line, etc. 
 

 

 

All the control of the parallel port is done through software. If 

you look at the hardware you find that the parallel port is connected 
directly to the computer bus. This means that we can address these 
inputs and outputs in any way we want if we do not use the port to 
drive a printer. 
 

 

 

 

Each PC has port addresses where the parallel ports, serial 

ports, hard disk, etc. can be addressed. These are located in the 
address range from 0000H to 03FFH (the H indicates the use of the 
hexadecimal numbering system). Each parallel port has one main 
port address for outputting data. The next two addresses above that 
address are used for handshaking control. For instance, on a typical 
computer a parallel port could be located at address 0378H. The 
handshaking lines will then be located at 0379H and 037AH. Table 1 
shows the correspondence between the bits of the port and the pins 
of the DB-25 female connector. 
 
 

Referring to Table 1, if you output a 01H (which is 00000001 

in binary) to your computer’s port 0378H, then pin 2 of the parallel 
port’s DB-25 connector will be HIGH and pins 3 through 9 will be 
LOW. To do this using GWBASIC you would use the command: 
OUT &H378,&H01. Using this method you can output any pattern 
you wish on pins 2 through 9 of the parallel port. To turn ON pins 2, 
4, 6, and 8 use:  OUT &H378,&H55. 55H is the same as 01010101 
binary. This port (0378H) can be read as an input, but mostly it is