Ampro Corporation P5X manual Parallel Port Registers, Standard and Bi-Directional Operation

Little Board/P5x Technical Manual

Please refer to the IEEE-1284 standard for the complete list of requirements for a compliant cable assembly, including recommended connectors

Latch-Up Protection

The parallel port incorporates chip protection circuitry on some inputs, designed to minimize the possibility of CMOS “latch up” due to a printer or other peripheral being powered up while the Little Board/P5x is turned off.

Parallel Port Registers

The low-level software interface to the parallel port consists of eight addressable registers. The address map of these registers is shown in Table 2– 21.

Table 2– 21. Parallel Port Register Map

Register Name	Address
Data Port	Base address
Status Port	Base address + 1
Control Port	Base address + 2
EPP Address Port	Base address + 3
EPP Data Port 0	Base address + 4
EPP Data Port 1	Base address + 5
EPP Data Port 2	Base address + 6
EPP Data Port 3	Base address + 7

Note: EPP registers are only accessible when in

EPP mode

Standard and Bi-Directional Operation

You can use the parallel port as a standard output-only printer port or as a PS/2-compatible bi- directional data port with up to 12 output lines and 17 input lines. The bi-directional mode can be very valuable in custom applications. For example, you might use it to control an LCD display, scan keyboards, sense switches, or interface with optically isolated I/O modules. All data and interface control signals are TTL-compatible.

Set the parallel port’s default mode using Setup.

Using the Parallel Port in Bi-Directional Mode

To use the port as a bi-directional data or digital control port you must set the default mode to bi- directional in Setup or put it in bi-directional mode with a BIOS call. The following code example shows how to set the parallel port mode to bi-directional.

2–27