Model-specific configuration registers
Placement of configuration values

"~" means the bit is a negated boolean. Sometimes values overlap,
depending on MCU model.

In STC12A series, the first 4 MCS bytes have active
values. Generally, unused bits should be set to 1.

MCS0
----

MSB     7       6       5       4       3       2       1       0       LSB
                                                        CLKSRC

CLKSRC := clock source (0 = internal RC, 1 = external crystal)


MCS1
----

MSB     7       6       5       4       3       2       1       0       LSB
                        ~WDEN           ~WDSTP  WDPS2   WDPS1   WDPS0

~WDEN := watchdog enable after power-on-reset
~WDSTP := stop watchdog counter in idle mode

WDPS2   WDPS1   WDPS0   divisior
0       0       0       2 
0       0       1       4
0       1       0       8
0       1       1       16
1       0       0       32
1       0       1       64
1       1       0       128
1       1       1       256


MCS2
----

MSB     7       6       5       4       3       2       1       0       LSB
                                                        ~EERE   ~BSLD

~EREE := enable eeprom erase next time MCU is programmed
~BSLD := enable BSL pin detect; i.e. BSL is only enabled if P1.0/P1.1
         (or others, depends on MCU model) are held low on POR.


MCS3
----

Unused.


MCS4
----

MSB     7       6       5       4       3       2       1       0       LSB
                LVD

LVD := low voltage detection threshold

LVD     threshold
0       3.7V
1       3.3V