Specifications

CoreModule/PC Technical Manual

4-10

DMA channel 0 is used to refresh DRAM in a “standard” PC. A handshake line for DMA 0,

-REFRESH, is used by some expansion cards to detect when refresh is occurring.

The +12VDC, -12VDC, and -5VDC voltages of the PC bus are not required by the CoreModule/PC,

and are not generated by the CoreModule/PC for the PC expansion bus (P1) connector. If those

voltages are required for expansion modules, they can be connected via the board's power connector

(J5).

All the other signals on the bus conform to what is found on a standard PC's expansion bus. For

details, consult the technical references listed in the beginning of this chapter, and Appendix B,

CoreModule/PC Bus Timing.

4.4 PARALLEL PORT

The parallel port on the CoreModule/PC is functionally identical to the parallel printer port of a

standard PC, except that the data lines can be made bidirectional by setting a mode bit in the control

All data and interface control signals are TTL compatible, and the port can be used as a general

purpose digital I/O port if not required for a printer. Applications might include controlling an

LCD display panel, scanning keyboards, sensing switches, and interfacing with optically isolated

I/O modules.

4.4.1 Using the Parallel Port as a Printer Port

This port is enabled using the SETUP function. During POST, the BIOS scans the parallel port I/O

addresses in the order 3BCh, 378h, and 278h. The CoreModule/PC's parallel port address is 378h.

If it is the only one found, it is assigned LPT1. However, should the system contain a parallel port

addressed at 3BCh, the parallel port on the CoreModule/PC will be installed as LPT2.

Normally, the parallel port interrupt request is not used, and is available for other devices if needed.

The ROM-BIOS disables the interrupt from the parallel port during initialization, prior to boot time.

The ROM-BIOS does not use the interrupt in printer data transfers. IRQ7 is the interrupt generally

assigned to the primary parallel port. On the CoreModule/PC this is a fixed assignment; no

physical jumpering is used.

When the port is disabled, its I/O port addresses and system interrupt become available on the PC

expansion bus for other devices in the system.

4.4.2 Using the Parallel Port as a Bidirectional I/O Port

It is also possible to use the parallel port as a bidirectional data port for use with custom software.

The eight data lines are truly bidirectional, the four control lines are quasi- bidirectional, and the

five status lines can be used as inputs.

A ROM-BIOS function has been provided that can be used to dynamically set the direction of the

printer port data lines during system operation. The following example shows a simple assembly

language routine that controls the parallel port direction: