Read Buffer (3C); Combined Header And Data (Mode 000) - IBM DDRS-39130 - Ultrastar 9.1 GB Hard Drive Specifications

7.18 READ BUFFER (3C)

Byte
7 6
0
1 LUN
2
3 (MSB)
4
5
6 (MSB)
7
8
9 VU = 0
Figure 97. R E A D B U F F E R (3C)
The READ B U F F E R command is used in conjunction with the WRITE B U F F E R command as a diag-
nostic function for testing the file's memory and the SCSI bus integrity. This command does not alter the
medium.
The function of this command and the meaning of fields within the command descriptor block depend on
the contents of the mode field.
MODE Description
000 Read combined header and data
010 Data
011 Descriptor
All others Not supported.

7.18.1 Combined Header And Data (Mode 000)

In this mode, a four byte header followed by data bytes are returned to the initiator during the DATA IN
phase. The Buffer ID and the buffer offset field are reserved.
The file terminates the DATA IN phase when allocation length bytes of header plus data have been trans-
ferred or when the header and all available data have been transferred to the initiator, whichever is less.
The four-byte READ B U F F E R header (Figure 98 on page 128) is followed by data bytes from the file's
data buffer.
Bit
5 4 3
Command Code = 3Ch
Reserved = 0
Buffer ID = 0
Buffer Offset
Allocation Length
Reserved = 0
2 1 0
Mode
(LSB)
(LSB)
FLAG LINK
SCSI C O M M A N D SET
127