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3.3.3
Field Scanning as MDS Control: MDS_control = 2
After a new start or a restart of the AS or after a new start or RESET command of the FC 45,
the write/read device is turned on and remains active until the AS or ASM is turned off.
The ASM continuously scans the field around the write/read device for the presence of a
data memory. When the ASM detects a data memory, the ANZ_MDS_present bit is returned
to the user during the next bus cycle or FC call. Similarly, ANZ_MDS_present becomes 0
when the data memory moves out of the write/read device's field.
If the data memory stops exactly on the border of the magnetic field of the write/read device,
there is no danger of ANZ_MDS_present switching back and forth continuously. This
hysteresis function is handled by the processor on the ASM.
Read/write commands can be sent to the FC 45 with complete transparency for the MDS
control. The ANZ_MDS_present variable also retains complete validity after the start of a
command.
Table 3-18
L, B:
h:
a:
b:
c:
FC 45
Function manual, Release 03/2006 , J31069-D0167-U001-A2-7618
Field scanning as MDS control
Dimensions of the transmission window of a write/read device at working distance to
MDS (see MOBY I configuration manual)
L = field length; B = field width
Hysteresis: Area in which an ANZ_MDS_present bit which has been set once
remains set
Point at which the mobile data memory is detected by the write/read device. From
this point on, the waiting MOBY command is processed with the MDS.
ANZ_MDS_present remains set.
The MOBY command must have been executed by this point since the data memory
is leaving the transmission window. ANZ_MDS_present still remains set.
Reset ANZ_MDS_present in control and status word. The MDS has left the
transmission window of the write/read device. A command which has still not been
processed is terminated, and ASM error 01 hex is generated.
Parameterizing
3.3 Presence check and MDS control
3-25
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