MC68HC711xxxx Motorola, MC68HC711xxxx Datasheet - Page 212

• Manufacturer Part Number: MC68HC711xxxx
• Description: Microcontrollers
• Manufacturer: Motorola

Application Note
Bootstrap Mode Logic
212
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.
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
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.
shows the composite memory map of the MC68HC711E9 in its
Table 1
shows the relationship between the state of these
AN1060 — Rev. 1.0
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