This section lists the pinout of the parallel port connector and describes how to configure it for its I/O port and interrupt assignments, how to assign a DMA channel to the port when operating in ECP mode. And programming information, including how to use the port for
I/O Addresses and Interrupts
The parallel port functions are controlled by eight I/O ports and their associated register and control functionality. The Little Board/P5x parallel port is assigned to the primary parallel port address normally assigned to LPT1 and cannot be changed. You may disable the port in Setup to free the hardware resources for other peripherals.
The parallel port can be configured to generate an interrupt request upon a variety of conditions, depending on the mode the port is in. Assignment of an interrupt to the parallel port is optional, and its use depends on software requirements and which mode of operation you are using. IRQ 7 is the default parallel port IRQ assignment.
Table 2– 20 lists the parallel port addresses and IRQs.
Table 2– 20. Parallel Printer I/O Addresses and Interrupt
Selection | I/O Address | Interrupt |
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Primary | 378h - 37Fh | 7 |
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Secondary | 278h - 27Fh | 5 |
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Secondary | 3BCh - 3BFh | 7 |
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Disable | None | None |
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ROM-BIOS Installation of Parallel Ports
Normally, the BIOS assigns the name LPT1 to the primary parallel port, and LPT2 to the secondary parallel port (if present), and so on. However, the BIOS scans the standard addresses for parallel ports and if it only finds a secondary port, it assigns LPT1 to that one. Therefore, if the Little Board’s parallel port is enabled, it will be assigned LPT1 by the BIOS. If it is disabled and there is another parallel port in your system, that port will be assigned LPT1 by the BIOS.
The
DMA Channels
In ECP enhancement mode, the parallel port can send and receive data under control of an on- board DMA controller. DMA channels operate with a request/acknowledge hardware handshake protocol between an internal DMA controller and the parallel port logic. On the Little Board/P5x, select a DMA channel in Setup. You can configure the parallel port to use either DMA channel 1 or DMA channel 3.
If you will not be using DMA with the parallel port, leave it disabled. This makes the DMA channel available to other peripherals installed on the expansion buses.
