On the startup line, specify the socket to listen on:
./basic SOCKET=socket IPLFILE
Where socket is a numerical socket value to listen on.
ERR=13 results when trying to READ or WRITE to a socket if no socket was specified at startup (see code below).
This is a listening (i.e. passive) socket, so a READ is done first on channel 0 as shown in the following example:
>READ(0, OPT="SOCKET" [,TIM=timoutval]) A$
You can perform multiple READ and WRITE directives. The conversation is only terminated with:
>WRITE(0,OPT="SOCKET|CLOSE") "some data going back"
Using the TIM= option is recommended to prevent the appearance that Basic hangs. If no TIM= is present, the READ will wait for a connection indefinitely