MC68HC711E20CFS2 MOTOROLA [Motorola, Inc], MC68HC711E20CFS2 Datasheet - Page 224

• Manufacturer Part Number: MC68HC711E20CFS2
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Application Note
Allowing for Bootstrap Mode
Mode Select Pins
RESET
RxD Pin
224
Since bootstrap mode requires few connections to the MCU, it is easy to
design systems that accommodate bootstrap mode.
Bootstrap mode is useful for diagnosing or repairing systems that have
failed due to changes in the CONFIG register or failures of the expansion
address/data buses, (rendering programs in external memory useless).
Bootstrap mode can also be used to load information into the EPROM or
EEPROM of an M68HC11 after final assembly of a module. Bootstrap
mode is also useful for performing system checks and calibration
routines. The following paragraphs explain system requirements for use
of bootstrap mode in a product.
It must be possible to force the MODA and MODB pins to logic 0, which
implies that these two pins should be pulled up to V
rather than being tied directly to V
to V
hard wired for. It is also good practice to use pulldown resistors to V
rather than connecting mode pins directly to V
sometimes a useful debug aid to attempt reset in modes other than the
one the system was primarily designed for. Physically, this requirement
sometimes calls for the addition of a test point or a wire connected to one
or both mode pins. Mode selection only uses the mode pins while
RESET is active.
It must be possible to initiate a reset while the mode select pins are held
low. In systems where there is no provision for manual reset, it is usually
possible to generate a reset by turning power off and back on.
It must be possible to drive the PD0/RxD pin with serial data from a host
computer (or another MCU). In many systems, this pin is already used
for SCI communications; thus no changes are required.
In systems where the PD0/RxD pin is normally used as a general-
purpose output, a serial signal from the host can be connected to the pin
Freescale Semiconductor, Inc.
DD
For More Information On This Product,
, it is not possible to force a mode other than the one the MCU is
Go to: www.freescale.com
DD
. If mode pins are connected directly
SS
because it is
DD
through resistors
AN1060 — Rev. 1.0
MOTOROLA
SS