Reference Guide

Chapter 3 Transport Layer Implementation Details
Parallel SCSI
DLT-S4 Interface Reference Guide 15
The drive’s minimum supported value for Transfer Period is 0Ah when
the bus is operating in LVD mode. When operating in SE (Single-Ended)
mode, the minimum Transfer Period value is 0Ch.
When the Transfer REQ/ACK value is non-zero, the drive will transfer
data using synchronous transfers; a Transfer REQ/ACK offset value of
zero indicates asynchronous transfers. If the host requests a Transfer
REQ/ACK offset value greater than the maximum value that the drive
supports, the drive responds with the maximum value that it supports.
Parallel Protocol Request 3 Parallel Protocol Request (PPR) messages (as shown in figure 2) are used to
negotiate synchronous transfer agreements and wide data transfer
agreements, and to set the protocol options between two SCSI devices.
Figure 2 Parallel Protocol
Request Message — Data
Format
The PPR message is required to configure an DLT-S4 tape drive. This
command sets the transfer period, offset, transfer width, and clocking all
in one message.
Support for the PPR message is indicated by the Clocking field in the
Standard Inquiry page. The PPR message can also be used to set the
transfer period, offset, and transfer width on an DLT-S4 tape drive with
Bit
Byte
7 6 5 4 3 2 1 0
0 Extended Message Identifier (01h)
1 Extended Message Length (06h)
2 Parallel Protocol Request (04h)
3 Transfer Period Factor
4 Reserved
5 REQ/ACK Offset
6 Transfer Width Exponent
7 Reserved DT_REQ Reserved