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6GT2 097-3AH00-0DA2
5.1
MDS recognition by field scanning
EAKO = '0'
How field scanning works
The SLG scans the surrounding area for the presence of a data carrier. If the file handler recognizes a data
carrier, the ANW bit will be set and a Z telegram sent to the user.
After the MDS has left the transmission window, the ANW bit will be reset and a Z telegram will be sent to
the user, while the SLG scans the field for the next MDS.
If the data carrier remains exactly on the border of the transmission window, a hysteresis function ensures
the ANW bit does not continuously toggle between on/off. This hysteresis function is handled by the pro-
cessor on the ASM. Read/write commands are handled completely transparently by the ASM and have no
effect on proximity detection.
L
MDS
L, B: Dimensions of the transmission window of an SLG
read/write device at operational distance to MDS (See
manual for configuration, installation and service.)
L = Field length; B = Field width
h:
Hysteresis: Area in which a just set ANW bit remains set.
a:
The point at which the mobile data carrier is detected by the SLG. The pending MOBY command will
now be processed on the MDS. The presence bit is set. The user can receive an ANW message if
required (Z message).
b:
The MOBY command must be completed by this point as the data carrier is about to leave the trans-
mission window. The presence bit is still set.
c:
The presence bit is reset. The user receives a Z message. The MDS has passed out of range of the
SLG.
Subject to change without notice!
RD: 03/02
J31069-D0142-U001-A0-7618
B
SLG
c
b
h
a
– 50 –
ASM 421 Technical Description
b
Hysteresis field for
proximity detection
Transmission window:
Data exchange between
MDS and SLG
h = 0.1 ... 15 mm
(depends on MDS type)
6GT2 002-0DA00
6GT2 002-0DB00
6GT2 002-0DC00
ASM 421 / V.24
ASM 421 / RS422
ASM 421 / TTY
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