AN OFF TOPIC - OH My GOSH!
Some cheapo computers only use +5V for a "psuedo RS-232" signal. RS-232 defines a "true" value as +12V not +5V! Some "cheapo" computers simply do not supply enough voltage on their "quote RS-232 ports" to be interfaced with compliant devices. Be aware of this - I've seen it.

Wrong. +5V is a perfectly valid RS232 voltage. The problem is (a) hardware that uses 0 V instead of -3V..-15V and (b) hardware that expects RS232 lines to deliver significant amounts of energy.

RS232 is specified to use +3V..+15V and -3V..-15V. The range -3V..+3V is undefined. RS232 is not specified to deliver significant current.

Legacy PC hardware is a completely different thing. Most PC "RS232" interfaces accept any voltage around 0V and below as negative (this does not violate the RS232 spec), and the outputs can deliver several mA at +/-12V, simply because the original IBM PC was build this way, and legacy hardware (mostly serial mice and barcode readers) expect this interface. Some "exotic" systems (e.g. early laptops) had a different line driver circuit that delivered only +/-5V and/or less current, this caused compatibility problems with hardware that expected +/-12V and high current, mostly serial mice. Never the less, the interface was implemented according to the RS232 spec, but the peripheral device was not.

See also Re^2: Win32::SerialPort v. New computers.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

In reply to Re^3: Write timeout, in perl Win32::Serialport by afoken
in thread Write timeout, in perl Win32::Serialport by prody001

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