50g serial port tech. - Help.

[ilkka777]

(01-06-2017 10:44 AM)Vtile Wrote:  PPPPS. Edit. for the above closeIO question.. If I take as a working hypothesis that my 2nd calculator is behaving correcty I must have been encountered to that Receive (RxD) line turns to sink (pulled down through resistor I assume) when you run the CLOSEIO command. While making loopback connection (RxD&TxD wired together), it drives Transmit line down to near 1.8 volts, which on the scope looks like a zero while using +-20 volts FSD setting.
Now this chapter is speculation unless someone can confirm or deny it.

Can you remember, how did you solve this? I have similar problem and I dont understand why the HP39GS TX line goes to around 1.6V when connected to pulled down line in arduino