
Application Note
AN1060 — Rev. 1.0
212
MOTOROLA
system, including components and circuitry external to the embedded 
MCU. If any problems appear during product development, diagnostic 
programs can be downloaded to find the problems, and corrected 
routines can be downloaded and checked before incorporating them into 
the main application program. 
Bootstrap mode can also be used to interactively calibrate critical analog 
sensors. Since this calibration is done in the final assembled system, it 
can compensate for any errors in discrete interface circuitry and cabling 
between the sensor and the analog inputs to the MCU. Note that this 
calibration routine is a downloaded program that does not take up space 
in the normal application program. 
Bootstrap Mode Logic
In the M68HC11 MCUs, very little logic is dedicated to the bootstrap 
mode. Consequently, this mode adds almost no extra cost to the MCU 
system. The biggest piece of circuitry for bootstrap mode is the small 
boot ROM. This ROM is 192 bytes in the original MC68HC11A8, but 
some of the newest members of the M68HC11 Family, such as the 
MC68HC711K4, have as much as 448 bytes to accommodate added 
features. Normally, this boot ROM is present in the memory map only 
when the MCU is reset in bootstrap mode to prevent interference with 
the user’s normal memory space. The enable for this ROM is controlled 
by the read boot ROM (RBOOT) control bit in the highest priority 
interrupt (HPRIO) register. The RBOOT bit can be written by software 
whenever the MCU is in special test or special bootstrap modes; when 
the MCU is in normal modes, RBOOT reverts to 0 and becomes a read-
only bit. All other logic in the MCU would be present whether or not there 
was a bootstrap mode. 
Figure 1
 shows the composite memory map of the MC68HC711E9 in its 
four basic modes of operation, including bootstrap mode. The active 
mode is determined by the mode A (MDA) and special mode (SMOD) 
control bits in the HPRIO control register. These control bits are in turn 
controlled by the state of the mode A (MODA) and mode B (MODB) pins 
during reset. 
Table 1
 shows the relationship between the state of these 
F
Freescale Semiconductor, Inc.
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n
.