- 49 -
Design and Functions
Fig. 27 shows an overview of the bidirectional bus timing. The details, especially the time of the bus take-over
and release, are shown in Fig. 28. A more detailed description of the time symbols and the specific limit values
are listed in Table 8.
Fig. 27: Overview of the bus timing. A = transmission data channel A; B = transmission data channel B; E = floor infor-
mation of evaluation unit.
Fig. 28: Bus Timing Details (not to scale)
Table 8: Description of the timing symbols (at 25°C, if not stated otherwise)
Symbol Description
Min
Typ
Max
Unit
t
M
Message transmission interval
4
ms
t
A
Transmission segment A … C by channel A
347
µs
t
B
Transmission segment D … F by channel B
608
µs
t
E
Transmission floor information from evaluation unit
87
µs
t
P
Pause time until the evaluation can put the floor infor-
mation on the bus
1
.
150
(at 70°C)
µs
t
C
Time shift due to omitted comparison between the
channels in single-channel mode.
276
µs
t
S
Lag between take-over of the RS-485 bus and start bit
of the first data bit channel A.
2
12
µs
t
H
Time to hand-over the bus from channel A to channel B
(from stop bit of last symbol of channel A until start bit
of first symbol of channel B).
55
75
µs
t
R
Delay bus release (from stop bit of the last symbol until
bus driver is switched to high impedance).
7
9
µs
9.5.5
Presence Detector Magnetic Tape (only semi-guided variant)
The presence detector serves to assure that the magnetic tape is in the correct position and stays there. Using
the appropriate mechanics it is possible to detect the following faults:
1
The evaluation unit may only occupy the RS-485 bus after t
P
has elapsed because LIMAX44 RED cannot process the infor-
mation earlier.
Dual-channel operation:
Single-channel operation:
LIMAX44 RED is driving the bus
Evaluation unit is driving the bus
t
P
t
B
E
A
B
A
t
t
M
A
A
t
C
t
E
t
A
t
B
A
B
t
S
t
H
t
t
R
start bit
stop bit
bus driver on
bus driver off
