Datasheet

Operating Modes and Resource Mapping
M68HC12B Family Data Sheet, Rev. 9.1
78 Freescale Semiconductor
5.4 Mode and Resource Mapping Registers
This section describes the mode and resource mapping registers.
5.4.1 Mode Register
The mode register (MODE) controls the MCU operating mode and various configuration options. This
register is not in the map in peripheral mode.
Read: Anytime
Write: Varies from bit to bit
SMODN, MODB, MODA — Mode Select Special, B, and A Bits
These bits show the current operating mode and reflect the status of the BKGD, MODB, and MODA
input pins at the rising edge of reset.
SMODN can be written only if SMODN = 0 (in special modes) but the first write is ignored; MODB,
MODA may be written once if SMODN = 1; anytime if SMODN = 0, except that special peripheral and
reserved modes cannot be selected.
Table 5-2. Mapping Precedence
Precedence Resource
1 BDM ROM (if active)
2 Register space
3RAM
4 EEPROM
5 FLASH EEPROM/ROM
6External memory
Address:
$000B
Bit 7654321Bit 0
Read:
SMODN MODB MODA ESTR IVIS EBSWAI 0 EME
Write:
Reset states:
Normal expanded narrow: 1 0 110000
Normal expanded wide:11110000
Special expanded narrow: 0 0 111001
Special expanded wide:01111001
Peripheral:01011001
Normal single-chip:10010000
Special single-chip:00011001
Figure 5-1. Mode Register (MODE)