Brian,
Many PC related "RS-232" ports and devices do not conform to the
switching levels of RS-232 standard.
Yes, that means they will work, but only over short distance cables
(which is the norm in the PC world).
If the recieving end is clamping the voltage, it should not reduce the
noise immunity unless it is taking significant current from the driver.
There are factors involved other than the voltage - like the slope of
the positive going pulses.
73,
Don W3FPR
On 3/15/2013 3:40 PM, Brian Alsop wrote:
Guys,
Looking for some insight.
I was doing some checkout of a device. The device output a +10/-10V
RS232 signal swing from a MAX232 device.
When it was attached to a PCI serial port card, the output dropped to
+2.5/-10 V. In other words, the PCI card was clamping the input
positive value. It does work OK even clamped like this.
I'm guessing the internal chips are low voltage devices.
I though one of the redeeming values (for hams at least) of the
+15/-15 volt RS232 spec was noise immunity. Clamping it to 2.5 Volts
means considerably less noise (RFI) immunity?
True we do get along with lots of 5V TTL stuff.
73 de Brian/K3KO
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