
Operating Modes
Internal Resource Mapping
68HC(9)12DG128 Rev 1.0
MOTOROLA
Operating Modes
75
17-modes
ROMHM — FLASH EEPROM (68HC912DG128) / ROM
(68HC12DG128) only in second Half of Map
This bit has no meaning if ROMON bit is clear.
0 = The 16K byte of fixed Flash EEPROM / ROM in location
$4000–$7FFF can be accessed.
1 = Disables direct access to 16K byte Flash EEPROM / ROM from
$4000–$7FFF in the memory map. The physical location of
this16K byte Flash / ROM can still be accessed through the
Program Page window.
For 68HC912DG128 in special mode, with ROMTST bit set, this bit
will allow overlap of the four 32K Flash EEPROM arrays and overlap
the four 4-byte Flash register space in the same map space to be able
to program all arrays at the same time. For 68HC12DG128 this bit
offers no practical use in special mode and with ROMTST bit set,
however it must be set to 0 for proper reading of the ROM array under
this condition.
0 = The four 32K Flash / ROM arrays are accessed with four pages
for each.
1 = The four 32K Flash / ROM arrays coincide in the same space
and are selected at the same time for programming.
CAUTION:
Bit must be cleared before reading any of the arrays or registers.
ROMON — Enable FLASH EEPROM (68HC912DG128) / ROM
(68HC12DG128)
These bits are used to enable the Flash EEPROM / ROM
0 = Disables Flash EEPROM / ROM in the memory map.
1 = Enables Flash EEPROM / ROM in the memory map.
0
1
1
1
0
2
1
1
3
Table 17 EXSTR Stretch Bit Definition
EXSTR1
EXSTR0
Number of E Clocks
Stretched