+-------+                       +-------+
T.CSR:  |       |-------------> RCSR:   |       |
        +-------+                       +-------+
                                RDAT:   |       |
                                        +-------+
                                XCSR:   |       |
                                        +-------+
                                XDAT:   |       |
                                        +-------+
 
        +-------+
$XTTNR: |       |-------------> TNRRTN: RETURN 
        +-------+
 
        +-------+
$XTTPS: |       |-------------> TPSRTN: RETURN 
        +-------+
 
        +-------+
$XTTPB: |       |-------------> TPBRTN: RETURN 
        +-------+