The ASR-X has thru-holes on the motherboard for a 10-pin
header.  It is labeled J70.
I theorize that this could be a
debug header.  I traced
each of the pins back to the 68340 CPU, and this is the
apparent pinout of the header.  Note pins 8 and 10 
are serial signals...what baud rate?  No one knows yet!

Pin	 Signal    Meaning
--------------------------
1	 CS3_N     Device (debugger) Select (CPU output)
2	 IRQ7_N    Interrupt (CPU input)
3	 RTSB_N    Serial port (flow)
4	 RxRDY_N   Serial port (flow)
5	 RTSB_N    Serial port (flow)
6	 TxRDYA_N  Serial port (flow)
7	 DACK2_N   Device Acknowledge (CPU input) CPU detects debugger presence
8	 RxDB      Serial port (data in)
9	 RTSB_N    Serial port (flow)
10	 TxDB      Serial port (data out)

Talking with long-time experts (thanks Al, and Rick of A.S. in MA),
I've learned that many embedded 68K systems have debug or diagnostic
ports implemented in a similar way.  On powerup, the software attempts
to read from the debugger by enabling CS3_N.  If the debugger is there,
it will assert DACK2_N.  

So in order to use this debugger port, we need two things:
1) to assert DACK2_N by bringing it low on powerup.
2) to connect a DB-9 serial port to the header, and read it from a PC terminal
program.