PROCEDURE VRCSPA(VAR Task_Name:Rad56; Var Buff:CH512 );
   EXTERNAL;
{*USER*
 Pascal-3 procedure to receive a variable 512-byte data packet.
If no packet available, the task enters the 'STOPPED' state,
from which it returns only through an UNSTOP directive (USTP$).
If Task_Name[1]=0, then the first pending
receive data packet is returned, and Task_Name is set to the name
of the sender of that packet. If Task_Name is non-zero on entry, then
only packets sent by that task will be returned. In this case, an
I$DSW indicating 'no packet pending' means no packet FROM THE SPECIFIED
TASK is pending.
 
Task_Name must be in RAD50 format.

The length of the data packet received is encoded in the $DSW. Subtract
two from the integer value of $DSW and this will be the number of words
received. 
 
This procedure directly implements executive directive VRCS$.
Return status is available in $DSW.
}