B&B Electronics Parallel Printer Card PIOC Manuale Utente Scaricare il pdf (Pagina 15)

Interfacing the Standard Parallel Port http://www.senet.com.au/~cpeacock

Interfacing the Standard Parallel Port Page 15

Printer Mode is the most basic mode. It is a Standard Parallel Port in forward mode only. It

has no bi-directional feature, thus Bit 5 of the Control Port will not respond. Standard & Bi-

directional (SPP) Mode is the bi-directional mode. Using this mode, bit 5 of the Control Port will

reverse the direction of the port, so you can read back a value on the data lines.

EPP1.7 and SPP Mode is a combination of EPP 1.7 (Enhanced Parallel Port) and SPP Modes.

In this mode of operation you will have access to the SPP registers (Data, Status and Control) and

access to the EPP Registers. In this mode you should be able to reverse the direction of the port using

bit 5 of the control register. EPP 1.7 is the earlier version of EPP. This version, version 1.7, may not

have the time-out bit. See Interfacing the Enhanced Parallel Port

for more information.

EPP1.9 and SPP Mode is just like the previous mode, only it uses EPP Version 1.9 this time.

As in the other mode, you will have access to the SPP registers, including Bit 5 of the control port.

However this differs from EPP1.7 and SPP Mode as you should have access to the EPP Timeout bit.

ECP Mode will give you an Extended Capabilities Port. The mode of this port can then be set

using the ECP’s Extended Control Register (ECR). However in this mode from BIOS the EPP Mode

(100) will not be available. We will further discuss the ECP’s Extended Control Register in this

document, but if you want further information on the ECP port, consult Interfacing the Extended

Capabilities Port

ECP and EPP1.7 Mode & ECP and EPP1.9 Mode will give you an Extended Capabilities

Port, just like the previous mode. However the EPP Mode in the ECP’s ECR will now be available.

Should you be in ECP and EPP1.7 Mode you will get an EPP1.7 Port, or if you are in ECP and

EPP1.9 Mode, an EPP1.9 Port will be at your disposal.

The above modes are configurable via BIOS. You can reconfigure them by using your own

software, but this is not recommended. These software registers, typically found at 0x2FA, 0x3F0,

0x3F1 etc are only intended to be accessed by BIOS. There is no set standard for these configuration

registers, thus if you were to use these registers, your software would not be very portable. With

today’s multitasking operating systems, its also not a good idea to change them when it suits you.

A better option is to select ECP and EPP1.7 Mode or ECP and EPP1.9 Mode from BIOS and

then use the ECP’s Extended Control Register to select your Parallel Port’s Mode. The EPP1.7 mode

had a few problems in regards to the Data and Address Strobes being asserted to start a cycle

regardless of the wait state, thus this mode if not typically used now. Best set your Parallel Port to

ECP and EPP1.9 Mode.

Parallel Port Modes and the ECP’s Extended Control Register

As we have just discussed, it is better to set the Parallel Port to ECP and EPP1.9 Mode and

use the ECP’s Extended Control Register to select different modes of operation. The ECP Registers

are standardized under Microsoft’s Extended Capabilities Port Protocol and ISA Interface

Standard, thus we don't have that problem of every vendor having their own register set.

When set to ECP Mode, a new set of registers become available at Base + 0x400h. A

discussion of these registers are available in Interfacing the Extended Capabilities Port

. Here we are

only interested in the Extended Control Register (ECR) which is mapped at Base + 0x402h. It should

be stated that the ECP’s registers are not available for port’s with a base address of 0x3BCh.

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