
Write Count, Key, and Data
Hex Code
Data Address
Count
1D
The main storage location of the count (8
bytes), key and data bytes.
The number of bytes to write.
Description:
The Write Count, Key, and Data (CKD) command formats a new
record on the track. The first 8 bytes of the record are the count area: record ID
(5 bytes), key length (1 byte), and the data length (2 bytes). The remaining bytes
are written into the key and data areas.
The control unit requests an 8 byte count area from the channel. If the channel
sends fewer than an 8-byte count area, binary zeros fill the remaining bytes of the
count area. The write operation continues, using zeros for fields not transferred.
If the count area transferred from the channel contains eight bytes of X
'
FF
'
,
execution is terminated with unit check status. Sense data contains command
reject with format 0, message 4. The count area will not be written on the track.
The contents of the remainder of the track is unpredictable.
The key and data area lengths are defined in the count area. If the channel sends
fewer than (KL) + (DL) bytes, binary zeros fill the remaining bytes of the key and
data areas. If the key length (KL) is zero, the record formats without a key area. If
the data length (DL) is zero, the record formats as an end-of-file record.
If not followed by another Write CKD command, the remaining portion of the track
is erased.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
This command is not in a Locate Record or Locate Record Extended domain,
and is not preceded by one of the following:
– A Search ID Equal or Search Key Equal command that compares equal on
all bytes of the ID or key field.
Note:
A Read Key and Data, Read Data, Write Key and Data, or Write
Data command can be between the Search ID Equal and Write
CKD command. A Read Data or a Write Data command can be
between the Search Key Equal and the Write CKD command.
– A Write Record Zero command not in the domain of a Locate Record or
Locate Record Extended.
– A Write CKD command not in the domain of a Locate Record.
The file mask inhibits format write operations (bits 0 and 1 are ‘01’ or ‘10’).
This command is in a Locate Record or Locate Record Extended domain
specifying other than a Format Write (03) or a Write Track (0B) operation.
If the track does not have enough space for the complete record, the command is
terminated with unit check status. The sense data includes Invalid Track Format.
The track may contain a partial record. The residual byte count in the channel
status information may not show the amount by which the record length exceeded
the available space on the track.
4-86
Internal Disk Subsystem Reference Guide
Summary of Contents for Multiprise 3000
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