TFBS5700
Document Number 84670
Rev. 2.1, 25-Sep-06
Vishay Semiconductors
www.vishay.com
225
I/O and Software
In the description, already different I/Os are men-
tioned. Different combinations are tested and the
function verified with the special drivers available
from the I/O suppliers. In special cases refer to the
I/O manual, the Vishay application notes, or contact
directly Vishay Sales, Marketing or Application.
Programming Pulse duration Switching
After Power-on the TFBS5700 is in the default short
pulse duration mode. Some ENDECs are not able to
decode short pulses as valid SIR pulses. Therefore
an additional mode with an extended pulse duration
as in standard SIR transceivers was added in
TFBS5700. TFBS5700 is set to the “short output
pulse” as default after power on, also after recovering
from the shutdown mode (SD must have been longer
active than 1.5 ms). For mode changing see the fol-
lowing. To switch the transceivers from the short
pulse duration mode to the long pulse duration mode
and vice versa, the programming sequences
described below are required.
Setting to the ENDEC compatibility mode
with an RXD pulse duration of 2 µs
1. Set SD input to logic "HIGH".
2. Set TXD input to logic "LOW". Wait t
s
≥ 200 ns.
3. Set SD to logic "LOW" (this negative edge latches
state of TXD, which determines speed setting).
4. TXD must be held for t
h
≥ 200 ns. After waiting t
h
≥ 200 ns TXD.
TXD is now enable as normal TXD input for the longer
RXD - pulse duration mode.
Setting back to the default mode with
400 ns RXD-output pulse duration
1. Set SD input to logic "HIGH".
2. Set TXD input to logic "HIGH". Wait t
s
≥ 200 ns.
3. Set SD to logic "LOW" (this negative edge latches
state of TXD, which determines speed setting).
4. After waiting t
h
≥ 200 ns TXD is limited by the max-
imum allowed pulse length.
TXD is now enabled as normal TXD input.
The timing of the pulse duration changing procedure
is quite uncritical. However, the whole change must
not take more than 600 µs. See in the spec. “Shut-
down Active Time Window for Programming”
Simplified Method
Setting the device to the long pulse duration is nothing
else than a short active SD pulse of less than 600 µs.
In any case a short SD pulse will force the device to
leave the default mode and go the compatibility
mode. Backwards also an active SD can be used to
fall back into the default mode by applying that signal
for a minimum of 1.5 ms. That causes a power-on-
reset and sets the device to the default short pulse
mode. This simplified method takes more time but
may be easier to handle.
Figure 2. Mode Switching Timing Diagram
TXD
SD
t
s
t
h
50 %
Hig h:F IR
Low : SIR
50 %
50 %
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