
Read IPL
Description:
The Read Initial Program Load (IPL) command causes the
addressed logical volume to seek to cylinder 0, head 0. The logical volume then
reads the data area of the record following R0.
The Read IPL command sends the data field of the first record following record
zero on track 0000. The data is an IPL program status word and one or two
commands. The first command should be a Read command that reads the second
record on track 0000. If the IPL sequence must read or write additional records,
the second command must be a Transfer in Channel (TIC) command to a
command chain read into processor storage by the preceding Read command.
The Read IPL command operates like a Read Data (06) command that was
preceded by Define Extent and Locate Record commands with the following
parameters:
Define Extent:
– Mask byte is X
'
00
'
– Global attributes is X
'
C0
'
– Block size value is zero
– Beginning of extent address is zero
– End of extent address is the highest primary track address on the logical
volume.
Locate Record:
– Operation byte is X
'
86
'
– Auxiliary byte is X
'
00
'
– Count is X
'
02
'
– Seek address, search argument, sector number, and transfer length factor
are zeros.
Note:
If a reset occurs and the following selection is for a Read IPL command,
Internal Disk does not present reset notification for that selection. The reset
notification condition is cleared by the Read IPL command.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
This command is received in the domain of a Locate Record or Locate Record
Extended command.
This command was preceded in the same channel program by a Define Extent
or a Set File Mask command.
On a 3390 logical volume, another Read IPL command preceded this Read IPL
command in this command chain.
Ending Status:
The control unit presents channel end and device end status
when data transfer completes.
Hex Code
Data Address
Count
02
The main storage location for the
first data byte.
The number of data bytes to be
read.
4-76
Internal Disk Subsystem Reference Guide
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