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ASM 421 Technical Description
6GT2 097-3AH00-0DA2
– 35 –
RD: 03/02
6GT2 002-0DA00
ASM 421 / V.24
Subject to change without notice!
6GT2 002-0DB00
ASM 421 / RS422
6GT2 002-0DC00
ASM 421 / TTY
J31069-D0142-U001-A0-7618
3.4.8
COVER
1. The file structure of an MDS can be protected against unauthorized access. This means that com-
mands which cause changes in a checksum or create additional DIR or FAT entries can only be issued
by authorized users (superusers).
An unauthorized access includes the following:
– Files are deleted or set up.
– File lengths are shortened or lengthened.
– Data carriers are formatted although they have been formatted already.
– Attributes are deleted or new ones are assigned.
After generating the valid file structure on the MDS, an authorized user (superuser) must protect this
with the COVER command. This prevents other users from destroying checksums by accessing the
data carrier. An illegal command is rejected with error message D022.
2. If the superuser wants to format the MDS or delete/set up files, he/she must first “open” the data carrier
again with the COVER command.
3. A COVER command for an unformatted MDS is rejected with error D015.
4. Specification of a volume name (i.e., MDS name) with the COVER command ensures that a data car-
rier must be unmistakably identified by the superuser. The COVER command is rejected with error
D023 when the two MDS names (i.e., data carrier name and volume name in the COVER command)
are not identical. Specification of a user identifier (byte 19 in the command telegram) greater than
01 hex is rejected with error message D005.
Telegram to the file handler:
’C’
CC CI ADB DBN DBL
xx 00 0000
Volume
User
0
1
2/3
4
5
6/7
8/9
10
11/18
19
01H: The MDS is to be protected against unauthorized access.
00H: Changes to the MDS file structure are permitted again.
’I’
0001
09
0001
Acknowledgement:
’C’
CC Status ADB
DBN DBL
00
xx
0000
ADB
0
1
2/3
4
5
6/7
8/9
10
0001
00
00