A few scanning tips


Windows SCSI Tips

My SCSI scanner was not powered on at boot time

If your SCSI scanner was not powered on when you booted Windows, then Window's Plug and Play cannot see it.

But you can power the scanner on later, then go to the Control Panel - System - Device Manager. First expand the SCSI CONTROLLERS item and highlight the scanner's SCSI board there. Then click the big REFRESH button, and the scanner should then work after a few seconds. This requirement is not the scanner's fault at all, it is instead due to Windows counting all its hardware when it boots. Refresh will look again after the scanner is on. The scanner itself may or may not appear in the Device Manager list then, some do, some don't, it doesn't affect how they work.

In Win98 or ME, you can go directly to the Device Manager with a Right Mouse Button click on the My Computer icon, then Properties.   Guy Daugherty points out that a short cut to access the Device Manager is to hold down the "Windows" key and then hit the "Pause/Break" key.

At the Win XP Start menu, right click on the My Computer link, then Properties, then the Hardware Tab. Then in the Device Manager, right click on the device, and select "Scan for Hardware Changes" for Refresh, or there is a toolbar icon too.

NT 4.0 had a Control Panel applet "Tape Devices" with a "Detect" button that finds the SCSI scanner in a similar way.

Some scanner SCSI boards do not use an IRQ with some software. These polled devices therefore will not be in the Device Manager List. No problem, these drivers interface directly with the port, and do not suffer the problem anyway.

These methods will not work for scanners on the parallel port or USB port. However, some scanners provide their own utility to do this function.

Note that you should not use the Refresh button unless your computer is idle. Highlighting the SCSI Controller greatly minimizes the effect on the system, but otherwise, if the top line "Computer" is highlighted, the Refresh button checks and resets all of the hardware.

You do not have to select the SCSI board first, but if you highlight the top line "Computer", it will also reset all your hardware. It can take longer, and your printer and modem LEDs may blink, and it can disrupt the current activity. Refresh may cause your modem to hang up the phone line if online. Your printer LED's will flicker too, so active print jobs are probably at risk. If your fax modem is listening to the serial port, then Refresh may abort, may complain that TAPI has the serial port.

So your computer should be idle. Or you should highlight the SCSI controller item instead.

ASPI For Windows XP

Windows 9x always included ASPI, required by SCSI scanner drivers to communicate with the SCSI board. We never gave ASPI a seconds thought, we automatically always had it with Win9x. However, Windows 2000 and XP do NOT include ASPI, so it will be necessary that you must add it for a SCSI scanner.

Free from www.adaptec.com    (if they move it again, just search there for "ASPI")

Does your SCSI scanner hog your machine?

If you have an ISA SCSI card, then the odds are good that when scanning, probably your computer is 100% "BUSY", that is, you are unable to switch to a different program to do anything else for the duration of the scan. Some users don't mind this, they are intent on the scanning job, but it drives others wild.

In the general case, this is due to the PIO mode SCSI board (parallel port scanners will act the same).   PIO mode (Programmed I/O, the simplest boards like the Adaptec AVA-1502AE and 1505 cards) means that your computers processor has to do all of the work of transferring the data, byte by byte, every byte, and it stays quite busy keeping up.   PIO is much like parallel port devices and most IDE devices in this respect, that is, the computer CPU does all of the work.   A PIO board is what came with most SCSI scanners back when they shipped ISA cards, and they suffer this problem. This does not mean they don't work well, but they will make your computer be very busy when scanning. Most PCI SCSI cards today are DMA instead of PIO.

SCSI cards are available that can do DMA (Direct Memory Access) to move larger blocks of data directly from the card to memory itself, without going through the computer processor. Conversely, the PIO cards must give the data to the computers processor, byte by byte, and the computers processor must move the data to memory, which keeps the computer pretty busy, very few idle cycles are available for other jobs. DMA solves that problem.

ISA or PCI card -- refers to the type of motherboard slot connector.

PIO or DMA -- refers to if the computer CPU or the SCSI board controls the memory transfer.

There were very few ISA DMA SCSI cards (Adaptec 1540/1542 was one) because the ISA bus can only access 16 MB of memory, so it must be double buffered (CPU must move data a second time to the final memory location). Most PCI SCSI cards are DMA, but not all.

An inexpensive PCI DMA SCSI board that is extremely suitable for ASPI compliant scanners (which is all of them today, but the early scanners were exceptions) is the Adaptec AVA-2906 (the 2906 replaced the AHA-2902E, I think the 2902E is no longer available in retail channels). These are PCI boards with 10 MHz SCSI bus, named "Fast SCSI". The PCI bus is faster than any ISA card can be (Pentiums have the PCI bus. 486 typically do not, but a few did). Scanners cannot go 10 MHz, but the old ISA bus is limited to even less than the scanners, so you will see a little speedup with a PCI card (as compared to an ISA card). Not a lot, but a little in some cases. The AVA-2906 board is about $44 to $50 retail. The AVA-2902E had only an external connector (the E is for External), but the AVA-2906 has both external and internal connectors. These boards will operate up to 7 SCSI devices, if the cables are short enough. Three external devices each on 3 foot cables is more realistic due to cable length. The 10 MHz SCSI board will however tolerate longer cables than will the faster Ultra or Wide boards, forget about six feet cables with them.

The AVA-2902E and AVA-2906 boards will accept the DB-25 connector matching the cable that comes with many scanners, keeping the total cost down (since a new cable is not needed). Such a DMA PCI card will make a tremendous difference in being able to use the computer while the scanner is scanning. It still may not be quite 100% perfect in that regard, but will be day and night better, you will think it's great.

Other SCSI cards are also available that are "bus-mastering", meaning the SCSI board can control the SCSI bus itself. The bus-mastering SCSI card is basically a coprocessor, it has its own processor, and it can do many I/O commands to different devices at one time (as opposed to needing many instructions from the computer to do it). It can do most all aspects of the SCSI transfer by itself. DMA alone is good to give the computer processor some idle time, you will see a dramatic difference in being able to switch to other programs while scanning if this is important to you. But the bus-mastering card also provides DMA, and also allows your computers processor to be nearly fully idle and available for other multitasking duty while it is waiting on notification of completion from the SCSI card. The DMA feature is extremely desirable for a recordable CD-R or CD-RW device too.

These boards mentioned do not have a BIOS, so they cannot boot the computer from a SCSI hard disk. They can operate disks, but they cannot boot from them. There are models that do and can (AHA-2940) and they cost more. They are also typically Ultra SCSI (20 MHz) or UltraWide (40 Mhz). These are a headache for a scanner, because the Ultra spec for bus length is 1.5 meters (4.9 feet, total of internal plus external cables, below).


A PCI bus-mastering SCSI board is very desirable for more than one reason. The PCI card will be faster than an ISA card, simply because of the ISA bus limitations. And most are DMA boards, giving some idle cycles to the computer. A bus-mastering card will permit your computer to be mostly idle to do other things during the scan. These features offer a lot of appeal.

I certainly cannot speak about the full extent of compatibility for all scanner brands with all SCSI boards, and naturally you would want to check with your scanners tech support department to verify that your scanner will operate with a standard ASPI interface. The Adaptec AVA-2906 is one such standard ASPI board, the drivers are supported directly by Windows, and any scanner ought to work with it.   Do check first.

The high-end SCSI boards, the Ultra and the Wide cards, are really less suitable for a low speed external device like a scanner. It's much like putting a race horse in a pony ride, and there are often some problems, not entirely unexpected. The spec's for the maximum SCSI bus length is:

SCSI Type   Max bus length
Total of Internal plus External
SCSI-1 - 5 MHz   6 meters, 19.7 feet
SCSI Fast - 10 MHZ   3 meters, 9.8 feet
SCSI Ultra - 20 MHZ   1 to 3 devices - 3 meters, 9.8 feet
4 to 7 devices - 1.5 meters, 4.9 feet

Some users try to ignore this charts facts, but cable length is of course extremely important. The length in the chart is the overall bus length, the sum of the internal cable and the external cable length. Less length than this would be expected to perform better. Putting a 6 foot external cable on a Ultra board with a 3 foot internal cable is asking for trouble. The simple DB25 connectors used on many scanners (omits all the ground wires, signals are no longer on twisted pair wire for noise immunity) were added when all we had was 5 MHz SCSI-1 (not the best idea even then), and were never intended for a high speed bus, and are certainly a complication. On a UltraWide board, stepping the 68 pin external connector down to 50 pins is another problem, the other 18 pins must be properly terminated (higher quality conversion cables will do this properly). The termination specs prohibit having three cable "ends", and unfortunately the 68 pin internal bus, the 50 pin internal bus, and the 50 pin external bus are three. You can only use any two. And general timing problems of using the faster board with slower devices is a concern in some cases.

Adding an "active" terminator can make all the difference in proper performance on a Fast or Ultra bus. I use a Belkin F2N959-B active terminator ($31 at www.buy.com). This is a DB25 connector to fit many scanners.

If you use an Ultra or UltraWide board with a few internal devices, and if you have the extra motherboard slot and the extra IRQ, I would suggest that your performance satisfaction will be higher if you install an inexpensive second board (PCI DMA like Adaptec 2906 or 2910) for the scanner. You should realize that life is simple and sweet with a second FAST card for the external devices.

Copyright © 1997-2010 by Wayne Fulton - All rights are reserved.

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