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Macintosh Quadra SCSI Data Transfer

Q: My app is having trouble with Macintosh Quadra SCSI data transfers. It appears to be related to the SCSI-chip in the particular machine. Is there a Gestalt definition for the SCSI-chip?

A: To determine which SCSI chip is present, examine the 6th, 7th, and 21st bits of the gestaltHardwareAttr selector. To investigate hardware-dependent bit values, use the Gestalt DA, which is on the Developer CD.

Make sure your software doesn't read or write to the SCSI hardware directly. For example, the Quadra utilizes the 53C96, so it won't correctly interpret or queue a SCSIstat call. With the 53C96, you don't have access to the state of the SCSI bus lines. In implementation, the 53C96 is more abstract than the 53C80, and software no longer has access to the physical layers of the chip's instruction set. Your software should allow the SCSI Manager to handle the 53C96 chip/software interaction.

[Jul 01 1995]

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