PC PARALLEL PORT DESCRIPTION
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
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
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
PPIO2899 Manual | 3 |
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