+-----+
             +----------------+ PCE +------------------+
             |                +--+--+                  |
             |                   |                     |
             |                   |                     |
             |                +--+---+                 |
             +----------------+R3(RR)+-----------------+
PF12         |                +--+---+                 |         PF22
PF11         |                                         |         PF21
+---+       ++-+          +--+          +--+         +-++       +---+
|SW1+-------+R1+----------+R5+----------+R6+---------+R7+-------+SW2|
+---+       ++-+          +--+          +--+         +-++       +---+
             |                                         |
             |                                         |
             |            +--+          +--+           |
             +------------+R2+----------+R4+-----------+
                          +--+          +--+