ASM 421 Technical Description
6GT2 097-3AH00-0DA2
– 21 –
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
3.3
Blocking of long data sequences
Since it is not possible to work with telegrams of indefinite length, the telegram is formed into blocks, i.e.
telegrams are transmitted in segments.
Blocking can be used with READ, WRITE, UPDATE, QUEUE-WRITE, DIR and TRACE commands.
Blocking is controlled by the parameters ADB (no. of data blocks) and DBN (current data block no.) in the
telegram heading.
The file description immediately follows the DBL parameter in the first command telegram to the file
handler (DBN = 1). It contains the file name, start address and length of the file. The file description is
omitted from subsequent telegram segments (DBN > 1).
Schematic sequence (example WRITE):
’I’
0003
User data
1st command telegram from user to ASM
CC
CI
ADB
DBN
DBL
File description
The command consists of three telegram segments
00
0003
1st acknowledgement telegram from ASM to user
CC
CI
ADB
DBN
DBL
0001
0001
’I’
0003
User data
2nd command telegram from user to ASM
CC
CI
ADB
0002
00
0003
2nd acknowledgement telegram from ASM to user
CC
CI
0002
’I’
0003
3rd or last command telegram from user to ASM
CC
CI
0003
User data
0003
3rd or last acknowledgement tel. from ASM to user
CC
0003
Processing of 1st telegram
segment by the file handler on
the ASM 421
The user processes the acknow-
ledgement and issues the 2nd
command segment
Processing of 2nd telegram
segment by the file handler on
the ASM 421
The user processes the acknow-
ledgement and issues the 3rd
command segment
Processing of last telegram
segment and terminating the
command by the file handler on
the ASM 421
The command has been
processed
00
DBN
DBL
ADB
DBN
DBL
00
ADB
DBN
DBL
CI
ADB
DBN
DBL
00
00