Viper 60s Theory Of Operation And Maintenance Manual page 130

VIPER SCSI 60, 125 & 150 THEORY OF OPERATION AND MAINTENANCE
5.26 READ DATA BUFFER (3Ch)
The READ DATA BUFFER command returns the 4-byte READ DATA BUFFER header plus
the number of bytes specified by the Allocation Length field. This command is used in
conjunction with the WRITE D AT A BUFFER command as a diagnostic function for testing the
drive buffer memory and confirming the SCSI bus integrity. During performance of this
command, there is no access to the tape.
5.26.1 READ DATA BUFFER Command Descriptor Block
1
o
3
4
5
~-.-.-
..
6
7 Allocation Length (MSB)
8
Allocation Length (LSB)
9
X Link
5.26.2 Command Descriptor Block Field Description
Allocation
Length
BYTE
7 and 8
o
5-72
" this bit is set to 1, Byte 2 contains the number of
the buffer where the reading begins. Buffers are
numbered from 0 to 113 (71 h), and each buffer
contains 512 bytes of data.
These fields specify the maximum number of
bytes the Initiator allocated for returned data.
includes a four-byte header, which is transferred
first, followed by the READ DATA BUFFER data.
All transactions must be in multiples of512
(fixed-b!ock length), plus the 4 byte header.
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