I pointed out a while ago that the modern chips like the MAX232 have a
positive receiver threshold so TTL drive is fine for short runs.
73,
David
On 1/27/14 10:35 AM, Javier Herrero wrote:
On 27.01.2014 15:08, Attila Kinali wrote:
In practice, the receiver chip only has one power supply. It would
take
extra work to make the switching threshold below ground.
That's not correct. Standard transceiver chips (like the MAX232 family)
have an integrated charge pump to get a negative power supply.
Hello,
The venerable MC1489 does not need a negative supply, and can have a
threshold below ground, without too much complication.
http://www.onsemi.com/pub_link/Collateral/MC1489-D.PDF (the receiver
circuit diagram is shown)
On the other side, the MAX232 has positive thresholds in the receiver
side http://datasheets.maximintegrated.com/en/ds/MAX220-MAX249.pdf pag. 6
Regards,
Javier
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