I'm using interceptty to watch the serial port, so I am confident about what is really happening, and understand why you pointed out that trap. 
syswrite(FH, 45); #puts 0x34 0x35 onto the wire, as if I said '45'

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and I do call that tinkering. I'm probably wrong in here somewhere, though, usually am.

I'm not sure what I've done, but now syswrite(FH, pack('C', $packet)) is working. Will test more.

In reply to Re^4: syswrite numbers, not strings by akujbida
in thread syswrite numbers, not strings by akujbida

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