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Ok, getting the T is reassuring.

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To get an L, SA RTS must not be asserted, because T will obscure the L.

Then SA DCD must be asserted (+).

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If both RTS and DCD on the SA are asserted, i.e. when the pc port is open normally, only T will appear.

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Please look at the voltage.

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Do you see a positive voltage on SA DCD (DB25 pin 8)? (produced when pc RTS is asserted on pc DE9 pin 7)

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That is necessary for commands to be recognized by the SA.

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I have option 043, your option 023 may behave differently, but if you can configure your COPY button to plot to rs232 in CONFIG, then the SA should be able to transmit rs232 data when you press COPY, regardless of whether it can receive rs232 commands.

So then if you see the T, with your RealTerm port open, pressing COPY should transmit a lengthy burst of ascii plot data that should be displayed by RealTerm. That may be worth trying.

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I’m still not sure if your pc usb-rs232 adapter needs its DSR (DE9 pin6) asserted in order to transmit. I’m suspicious that the chip may need that control signal asserted in hardware even if the RealTerm software application is configured for no hardware flow control. My FTDI adapter does not. Try tying the adapter pin 6 to pin 8 (both driven by SA DTR pin 20).

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Ed

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Just a correction here.

The connections I have made are: