
MOTOROLA
3-4
CONFIGURATION AND MODES OF OPERATION
M68HC11
REFERENCE MANUAL
after a subsequent reset.
Some versions of the M68HC11 Family allow the CONFIG working register to be writ-
ten directly as a normal control register while operating in the special mode variations.
This capability is included primarily to accelerate product testing but could be useful to
the user in some applications. In versions that have this ability, the MCU could be reset
in one of the special modes. The CONFIG register could be checked or written to any
desired value; then the mode could be written to a normal mode to re-enable system-
protection mechanisms. This procedure is independent of the EEPROM byte and the
transfer during reset. Only some versions of the M68HC11 offer this capability. Risk
factors are associated with operating in a special mode; therefore, keep the time be-
tween reset and writing the mode control bits back to a normal mode as short as pos-
sible to minimize these risks.
3.2.2 The CONFIG Register
The CONFIG register is an unusual control register used to enable or disable ROM,
EEPROM, the computer operating properly (COP) watchdog system, and, optionally,
the EEPROM security feature of the MCU. Unlike ordinary control registers, CONFIG
retains its contents even when there is no power applied to the MCU. The contents are
retained when the MCU is completely removed from a system (e.g., when shipped
from the Motorola factory). In this way, the control bits in the CONFIG register are like
mask-programmed options. Unlike mask options, the contents of this register can be
altered after the MCU is manufactured to meet the customer’s specific requirements.
The CONFIG register is read like any other memory location. The contents of the work-
ing static register are returned on such reads as previously described. The CONFIG
register is erased and programmed like an EEPROM location rather than being written
as other registers. The programming and erase operations alter the EEPROM byte,
which does not alter the operation of the MCU until after a subsequent reset operation.
The programming and erase procedures, which are the same as those used to pro-
gram EEPROM locations, use the PPROG register and are discussed in
4.3 EE-
PROM
.
The following register and paragraphs describe the CONFIG register and control bits
of the MC68HC11A8. For specific information about the CONFIG register of other
M68HC11 Family members, refer to the technical summary for that member.
NOSEC — EEPROM Security Disabled
A special security feature is available on the MC68HC11A8 if it is requested at the time
a user submits a mask ROM pattern. Once this feature is enabled at the mask-pro-
gramming level, the user activates it by programming the NOSEC bit to zero. While
NOSEC is zero, the MCU can only be reset in single-chip modes (normal single chip
CONFIG —
System Configuration
$103F
BIT 7
0
0
6
0
0
5
0
0
4
0
0
3
2
1
BIT 0
EEON
NOSEC
See
3.2.1 Operation of CONFIG Mechanism
NOCOP
ROMON
RESET: