MC68HC11G5 Datasheet, PDF (32/195 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcontroller

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3.4.3 Special Bootstrap Mode
This special mode is established by having a logic zero level on both the MODB/V_kam pin and the
MODA/LIR pin at the rising edge of RESET. The ROMON bit in the CONFIG register is a one out
of reset in this mode, so that the user ROM appears in the map. The initial memory map which results
is also controlled by the state of three bits (RBOOT, SMOD, and MDA) in the HPRIO control register
which are initialized automatically by hardware prior to the rising edge on RESET.
Initial conditions affecting the memory map are:
ROMON = 1, RBOOT = 1, SMOD = 1, MDA = 0
3.4.4 Special Test Mode
This special mode is established by having a logic zero level on the MODB/V_kam pin and a logic one
level on the MODA/LIR pin at the rising edge of RESET. The ROMON bit in the CONFIG register
is a one out of reset in this mode, so that the user ROM appears in the map. The initial memory map
which results is actually controlled by the state of three bits (RBOOT, SMOD, and MDA) in the
HPRIO control register which were initialized automatically by hardware prior to the rising edge on
RESET.
Initial conditions affecting the memory map are:
ROMON = 1, RBOOT = 0, SMOD = 1, MDA = 1
3.4.5 Changing Modes
Changing the operating mode and the bits described above is subject to some restrictions in normal
modes. First of all, ROMON, RBOOT and SMOD will stay in their reset state. These bits cannot be
changed in the normal operating modes. In order to allow a user to have an expanded mode system
with the ROM on, the user is allowed to change MDA once only. This means that the user can bring
the device out of reset in single chip mode, and then write MDA to a 1, thus putting the part into
expanded mode with the ROM on (ROMON = 1).
If the user does not intend to change modes after coming out of reset, he may wish to write MDA
one time to the same state. As MDA may be written to only once; this will prevent an accidental write
from changing the mode at some later time.
In the special operating modes, ROMON, RBOOT and MDA may be written at any time to either 0
or 1. SMOD cannot be written back to a 1 after being written to a 0, because the part will no longer
be in a special mode.
3.5 SYSTEM CONFIGURATION
The MC68HC11G5 allows the user to configure the MCU system to his specific requirements via
hard wired options, such as the mode select pins, and via internal software programmable control
MEMORY AND CONTROL/STATUS REGISTERS
3-4
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