Connecting Serial Port D9 to the Backplane

[G8LHS]

I want to connect the serial port on my TW39/Serial (2.0) card to the backplane connectors instead of the front D9 connector. Table 10 in Section 5.8.1 of the documentation says the D9 data and control connections use the screw terminals A22 & 24 and C22 & 24. The note underneath the table then says I need to make a connection from the D9 to logic ground on A4 or C4.

On my backplane though there are no terminals for A4 or C4 and I can't see where to make that connection. Could somebody help me and advise where to find a logic ground?

Thanks in advance...

David