Adaptec AHA-1540/1542 SCSI Host Adapters (102927)

This article was previously published under Q102927

The Adaptec AHA-1540 and 1542 series adapters are popular SCSI hard disk controllers because they can connect SCSI devices to ISA and EISA type PC buses. This article provides some specific details concerning these adapters, their default configuration settings, and some distinctions between them.

Distinctions Between Adaptec Models

The sole distinction between the AHA-1540 and AHA-1542 models is that the AHA-1542 has a floppy disk controller built into the card. A letter after the model number indicates the chronological sequence in which the devices were manufactured. The AHA-1540A and 1542A models are the first in their series. These models are obsolete and not supported under Windows NT. The AHA-1540B and 1542B models are no longer manufactured by Adaptec, but they are supported under Windows NT. The AHA-1540C and 1542C models are the latest production models of these cards and are supported under Windows NT.

Suggested Default Adaptec Settings

Adaptec recommends you install the Adaptec 1540B, 1542B, 1540C, and 1542C using the default settings. The following table indicates the factory default settings for these models with differences between the two models noted. Also, the range of possible settings is included where appropriate:

Setting              Default                Range of Options
------------------   --------------------   -----------------------

SCSI Address         7                      0, 1, 2, 3, 4, 5, 6, 7

SCSI Parity          Enabled

Terminators          Installed (B Series)
                     Enabled (C Series)

DMA Channel          5                      0, 5, 6, 7

Interrupt Channel    11                     9, 10, 11, 12, 14, 15

AT Port Address      330h                   130h, 134h, 230h, 234h,
                                            330h, 334h

AT BIOS Address      DC000h, Enabled        DC000h, D8000h, D4000h,
                                            D0000h, CC000h, C8000h

DMA Transfer Speed   5 MB/second

Host Adapter Termination, Cabling and Other Considerations

The AHA-1540 and 1542 series adapters require that the first and last device on the SCSI bus be terminated. Devices in the middle of the SCSI bus need to have their terminators removed or disabled. Therefore, if you have only internal SCSI devices or only external SCSI devices, the host adapter must be terminated. If your system has both internal and external SCSI devices, the host adapter must not be terminated.

Termination on the AHA-1540B and 1542B adapters is disabled by removing the installed bus terminators. Termination on the AHA-1540C and 1542C adapters is configurable by a hardware switch or by the host adapter configuration software. The AHA-1540C and 1542C cards require active terminators. Active terminators work best with active components that conform to the SCSI-II standard.

The AHA-1540C and 1542C adapters are sensitive to the type of cabling. Cabling must conform to the SCSI-II standard which recommends an impedance of 110-132 ohms. Cable-related problems are likely to occur when using an external cable since external cables usually have an impedance of 60-80 ohms. Also, short external cables may help problems related to signal loss.

The AHA-1540 and 1542 adapters may use the same upper memory addresses as other installed devices such as network cards. To avoid memory conflicts it may be necessary to manually re-configure the adapter hardware by changing jumper settings, as the upper memory addresses are not software configurable on these adapters.

The Windows NT mini-port driver, AHA154x.SYS, is the same driver used for all the cards in this series. It is hard-coded to transfer data at 5 MB per second. Attempting to negotiate this setting through hardware or software configuration will have no effect.

NOTE: The AHA154x.SYS driver is also used for the MCA version of this adapter, the AHA-1640. This adapter is not supported on IBM PS/2 model 70 computers.

The AHA-1540B and 1542B adapters may require a BIOS and firmware upgrade. They were only tested with firmware revisions 3.10 and 3.20. Free BIOS and firmware upgrades are available from the Adaptec BBS: (408) 945-7727.

Adaptec Technical Support may be reached at (408) 945-2550.

The product included here is manufactured by Adaptec, Inc., a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding this product's performance or reliability.