Viper 60s Theory Of Operation And Maintenance Manual page 128

VIPER SCSI 60, 125
&
150 THEORY OF OPERA TlON AND MAINTENANCE
5.25.2 Command Descriptor Block Field Descriptions
BCVBit
Byte Transfer
BYTE DESCRIPTION
o
7 and 8
The BCV bit set to 1 indicates that Byte 2 contains the
number of the buffer at which writing is to begin. Buffers are
numbered from 0 to
113
(71 h).
Byte Transfer Length specifies the maximum number of
bytes transferred to the Target and retained in the buffer. It
contains a four-byte header followed by the Write Data
Buffer data. All transactions must be in multiples of 512
bytes (fixed block length). plus a 4 byte header.
A Byte Transfer Length of zero indicates that no WRITE
DATA BUFFER header and no WR ITE DATA BUFFER data
are transferred. This condition is not an error. It is also not
an error to request a Byte Transfer Length less than the
Available Length plus 4 (reported by the READ DATA
BUFFER Command); however, if the Byte Transfer Length
is greater than the Available Length plus 4 (E204h), the
drive returns Check Condition Status with a Sense Key of
Illegal Request.
5.25.3 WRITE DATA BUFFER Data Header
I
BITS
6
5 4 3
2
1
BYTE
5-70