M-Systems Flash Disk Pioneers 45-SR-001-01-7L What is Plug-and-play P&P SCSI?, What is a Scsi ID?

FFD 3.5" SCSI Flash Disk User Manual

Q: What is Plug-and-play (P&P) SCSI?

A:Plug-and-play SCSI is an extension of the generic plug-and-play specification. P&P is an approach for defining an auto-configuring environment for ISA boards. One of the key features of P&P- SCSI is SCAM.

Q: What is SCSI Configured AutoMagically (SCAM)?

A:SCAM is a protocol for automatic SCSI ID assignment. It is included in the SCSI-3 parallel interface drafts. The SCAM master (typically the host adapter) scans the bus for attached SCSI devices. For compatibility, it also needs to find and identify legacy ( standard) SCSI devices. This scan provides the SCAM master with a map of the attached devices, and it then assigns a valid soft ID to each SCAM-compliant SCSI device. The SCAM master keeps this device table in non- volatile memory to provide an identical ID setup for further boot processes.

Q: What is a SCSI ID?

A:Every SCSI device must have a unique ID on the bus. For this reason, most devices have three ID jumpers to set the SCSI ID from 0-7. With the exceptions of ID 0 and 7, there is no particular ID that must be assigned to a particular device type. Additionally, every ID can have up to seven subunits identified by a LUN (Logical Unit Number), enabling addressing multiple devices through a single ID.

Table 7: General Description of SCSI ID

ID Number

ID 7

ID 0

ID 1

ID 2 and up

Description

Reserved for the host adapter.

For a boot device, usually a hard drive.

Normally used for a second hard drive, although it is not required.

Used for other devices, for example, a CD-ROM.

Q: What is Termination and TRMPWR?

A:The SCSI bus needs to be terminated. This means that both ends of the bus must have a circuit of some sort to eliminate signal reflections that otherwise would occur from the physical ends of the bus. The termination circuit requires power, generally supplied by a line called TRMPWR or Termination Power on the bus. Typically, the TRMPWR source is the host adapter. However, multiple devices can supply TRMPWR without causing damage.

The old, passive termination (Alternative 1 in the SCSI-2 specification) came with SCSI-1 and consisted of a 220 Ω pull-up and a 330 Ω pull-down resistor on each signal.

Active termination (Alternative 2 in the SCSI-2 specification) consists of a 110 Ω resistor on each signal, pulled up to a 2.85V reference supply.

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