A5191HRTNGEVB
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9
Figure 9. Clock Skew
Even if your own time base is perfect, you still must plan
on a possible 35% shift in a bit boundary, since you don’t
have control over time bases in other HART devices.
Transmitter
The TxA modem pin is decoupled through a 100 nF
capacitor to pin 7 of IDC2. For certain applications, it might
be required to remove this capacitor and replace it by a 0
W
resistor. The output on this pin is a 500 mV
pp
signal
trapezoid waveform shown in Figures 10 and 11. This pin
can only drive impedances higher than 30 k
W
, and as a
consequence may need to be amplified to drive low
impedances. For a given implementation of a master or
slave, it may be required to remove C4 and replace it with a
0
W
resistor to allow the decoupling to occur elsewhere in
the master implementation.
The nominal frequency of the output is 1196.9 Hz for
“mark” and 2194.3 Hz for “space”. These frequencies are
dependent on the accuracy of the A5191 clock.
Figure 10. Output Waveform (Mark)
