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Parallel Interface - Overview
Parallel ports can be controlled in several different ways, supporting progressively
faster transfers, longer cabling and more devices. These different modes are normally
configured in the BIOS of a PC, accessed with a special key combination early in the PC's
boot process (eg F1, F10, Del...). The key combination varies between manufacturers so
please check your user documentation for instructions.
| Port Mode |
Speed MB/s |
Max # of Devices |
Max Cable Length |
Notes |
| SPP (Simple Parallel Port) |
0.15 |
1 |
2m |
Sometimes also referred to
as Compatibility mode (only supports data PC>peripheral), basic 4-bit port mode. |
| Bi-Directional |
0.30 |
1 |
2m |
Designed for
peripheral>PC communication, 8-bit port, sometimes referred to as "Enhanced".
Win95 Service Pack 1 (minimum) recommended. |
| EPP (Enhanced Parallel
Port) IEE1284 |
>1.0 |
4 |
10m |
Longer cables reduce port
speed; requires Win95/98; EPP is typically used for devices other than printers or
scanners (better at data which switches directions frequently). I/O managed in PC
hardware. |
| ECP (Extended Capability
Port) IEE1284 |
>1.0 |
4 |
10m |
Requires dedicated IRQ and
DMA channel (better in multitasking environment). Optimised for printers or scanners
(better at transferring large blocks of data quickly). I/O managed in PC hardware. Best
mode for recent peripherals as it will "negotiate down" to suitable port mode. |
| ECP+EPP |
>1.0 |
4 |
10m |
Enhanced mode which will
negotiate support for either type of device, normally includes compatibility mode settings
of 1.7 or 1.9/1284 (1.7 recommended for early Astra scanners). |
Recommended Parallel Settings for UMAX Astra Scanners
| Scanner Model |
Recommended Port
Mode (Troubleshooting Options) |
Notes |
| Astra 600P |
EPP (BiDirectional then
SPP/Standard) |
|
| Astra 610P |
EPP (BiDirectional then
SPP/Standard) |
May also work in ECP/EPP
(v1.7), which improves support for a pass-thru connected printer |
| Astra 1220P |
ECP or EPP (v1.7) |
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| Astra 2000P |
ECP or EPP (v1.7) |
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Note: These recommendations presume the
scanner is the only device connected to the parallel port. A number of other issues arise
when sharing a parallel port between a scanner and printer, which are covered in a separate technical note.
Resources Used by Parallel Ports - Resolving Conflicts
Most PCs share the same default setup for their parallel (LPT) ports, with common memory
addresses and IRQ settings (shown below). These can normally be changed within the PC
BIOS, but are useful to know as the Scanner Test utility can search at a specific I/O
address (but does not show the corresponding LPT number).
| Port |
Common Interrupt |
Common I/O Address |
| LPT1 |
IRQ7 |
3BC |
| LPT2 |
IRQ7 |
378 |
| LPT3 |
IRQ5 |
278 |
Note: In early 80x86 PCs, BIOS support is
normally provided for MDPA (Monochrome Display and Printer Adapter), at 3BC - in this case
the printer ports use addresses 378 and 278 for LPT1 and 2 respectively, with no support
for a third port. Always check in your System control panel Device List that there are no
conflicts with the parallel port (if there are you have almost certainly configured
another device to also use IRQ7!).
"Scanner Not Detected" - Troubleshooting Link Failures
The majority of problems with connecting a parallel scanner are caused either by an
inappropriate parallel port mode set in the PC BIOS, or by interference by a printer
driver sharing the LPT port (this second problem is discussed in a separate
technical note).
1. Reboot your PC and enter the BIOS setup screen (this varies between manufacturers, you
must check your PC's instructions or read the boot-up screen to find out the key
combination required, we won't know!). Search through the BIOS screens for any Printer
Port settings, and check the MODE setting. Refer to the table above for the correct
setting required by your scanner, or work through the settings:
SPP/Standard - is the simplest mode and is a reliable way to check the
scanner and parallel port are working. You MUST disconnect all other parallel devices in
this mode.
ECP/EPP or ECP+EPP or ECP - is the most advanced (and fastest) mode,
should negotiate down through the standards to the most suitable setting for each device
and provides the best support for port-sharing. In some BIOS you have a setting for EPP
(compatibility) Mode, which should be set to 1.7 (instead of 1.9/1284). This is the
preferred setting for the more recent Astra 1220P and 2000P.
EPP - this setting will normally use the (pre-ECP) v1.7 standard, and
will provide support for multiple devices including scanners (recommended for Astra 610P
and 600P). There are some limitations to port-sharing in this mode and some printer
features may have to be disabled (eg on-line monitoring utilities).
BiDirectional - a reliable setting for the earlier parallel scanners, but
it will not properly support port-sharing.
2. Disconnect any devices connected to the pass-thru port of the scanner, so that it is
the only device attached to the printer port (this is just to isolate the problem, most
plug-through devices can be supported).
3. Disable or remove the driver for any second parallel device (typically a printer), to
check if the driver is conflicting with the scanner software.
4. In case your PC has an usual I/O address configuration, try selecting each of the
memory addresses listed in the Scanner Test program in turn.
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