On 27.01.2014 19:33, Robert Atkinson wrote:
All the receiver chips I've looked at, ancient and modern, have only positive
thresholds. Most have single supplies and clamp the input at 1 diode drop
negative WRT common after an input current limiting resistor, see the MC1489
datasheet.
Hello,
Not exactly. If you check the MC1489 datasheet from On Semiconductor,
the thresholds can be programmed with the response control resistor and
can in fact be negative. (Figures 6 and 7 in the datasheet). The serial
input resistor forms part of a resistive divider with the feedback
resistor and the external resistor - not simply a current limiter to the
diode.
Regards,
Javier
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