![background image](http://html2.mh-extra.com/html/quantum/dlt-s4/dlt-s4_reference-manual_3531879050.webp)
Chapter 3 Transport Layer Implementation Details
Parallel SCSI
DLT-S4 Interface Reference Guide
16
an Ultra 2 interface card. To enable it, set the
MODE SELECT
Vendor
Specific EEPROM parameter EnablePPRMsg to 1.
The PPR message allows the host and target devices to negotiate
operating conditions of the SCSI bus. An DLT-S4 tape drive responds to a
PPR message with a reciprocal PPR message containing acceptable
parameters for the interface. An DLT-S4 tape drive never initiates a PPR
negotiation.
Details about how to configure the PPR message are shown in
figure 3
.
Figure 3 Features of the
Parallel Protocol Request
Message
Field Description
DT_REQ
Double Transition Clocking Request
. This bit indicates a
request for Double Transition Clocking, which means that
two units of data are transferred for each clock cycle.
Support for the PPR message is indicated by the Clocking
field in the Standard Inquiry page.
Transfer Width
Exponent
Valid transfer widths for the tape drive are 8 bits (transfer
width = 00h) and 16 bits (transfer width = 01h). Other
transfer widths are reserved.
Transfer Period
Factor
09h = 12.5 nsec transfer period, 40 MHz DT (Ultra160)
08h = 6.25 nsec transfer period, 80 MHz DT (Ultra320)
0Ah = 25 nsec Transfer Period, 40 MHz
0Ch = 50 nsec Transfer Period, 20 MHz
19h = 100 nsec Transfer Period, 10 MHz
32h = 200 nsec Transfer Period, 5 MHz