+-------+                       +-------+
$TTPS:  |       |-------------> XCSR:   |       |
        +-------+                       +-------+
 
        +-------+                       +-------+
$TTPB:  |       |-------------> XDAT:   |       |
        +-------+                       +-------+
 
        +-------+
$XTTPS: |       |-------------> TPSRTN: RETURN 
        +-------+
 
        +-------+
$XTTPB: |       |-------------> TPBRTN: RETURN 
        +-------+