![Siemens MOBY I ASM 421 Скачать руководство пользователя страница 51](http://html.mh-extra.com/html/siemens/moby-i-asm-421/moby-i-asm-421_technical-description_377253051.webp)
ASM 421 Technical Description
6GT2 097-3AH00-0DA2
– 49 –
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
5
Checking entry and exit of MDS in SLG transmission window
This chapter describes various procedures for recognizing when an MDS is within range of an SLG. The
user can use the procedure most appropriate for the application with the RESET command: EAKO (see
section 3.4.15).
The following table shows the various types of entry/exit checking:
If MDS detected by field
scanning
EAKO
MDS entry
MDS exit
Command executed
NEXT
command
necessary?
Continuous
MDS flow
control by file
handler
Has filehandler
recognized
defective MDS?
“0”
Field scanning
Field scanning
If MDS present
Yes
Yes
No
“1”
User
User
Immediate; error if no
MDS in field
No
No
Yes
“2”
DI0 on ASM
Field scanning
If MDS is present via
DI0; error if field
scanning does not
detect MDS
Yes
Yes
Yes
“3”
DI0 on ASM
DI1 on ASM
If MDS present
Yes
Yes
Yes
“4”
User
User
If MDS detected by field
scanning
No
No
No
“5”
User
User
No
No
No
General procedure for an SLG:
For each SLG that is to process an MDS, the station-specific SLG number is written to the system
area of the MDS. The SLG number is written automatically before the first command to be executed on
the MDS. The file handler recognizes from the SLG number whether a new or an old data carrier is cur-
rently present in the transmission window of the SLG.
New MDS:
SLG numbers (SLG no. on MDS and station-specific SLG no.) do not correspond
Old MDS:
SLG numbers correspond
Current MDS:
All active commands apply to this MDS
Next MDS bit:
Internal status flag in the file handler
ANW bit:
Presence bit; the status of this bit is indicated by the green LED and on the backplane
connector (z18). As an option, the user can receive an ANW message if the ANW bit
changes (Z message: switch-selectable parameter).
The old MDS remains current (all commands relate to this MDS) until it is closed by a NEXT command. All
subsequent commands refer on this SLG to the next new MDS. This is achieved by having the file handler
set the “next MDS bit” when it receives a NEXT command. If the old MDS reenters the SLG transmission
window as the next MDS (SLG numbers correspond), no command is issued (the “next MDS bit” remains
set). When a new MDS enters the transmission window, the “next MDS bit” will be reset and the
station-specific SLG number will be written to the system area of the MDS (the new MDS thus becomes
the old/current MDS).