AN2548 Freescale Semiconductor / Motorola, AN2548 Datasheet - Page 2

• Manufacturer Part Number: AN2548
• Description: Serial Monitor Program for HCS12 MCUs
• Manufacturer: Freescale Semiconductor / Motorola

AN2548/D
Block Protection
Oscillator Configuration
COP Configuration
2
NOTE:
the MCU speed without consideration for the monitor program will render the
monitor nonfunctional. If the PLL loses lock during operation, the monitor will
fail.
With the exception of mask set errata documents, if any other Motorola
document contains information that conflicts with the information in the device
guide, the device guide should be considered to have the most current and
correct data.
To prevent accidental changes to the monitor program itself, the 2-Kbyte block
of FLASH memory residing at $F800–$FFFF is block protected. The only way
to change the contents of this protected block is to use a BDM-based
development tool.
In the lowest-cost applications where the monitor is used with an SCI serial
interface to the RS-232 serial port on a personal computer, there is no way to
accidentally erase or modify the monitor software.
Because the security and backdoor keys are stored in the protected block,
these functions are disabled. Though it is possible to edit the source code to
enable these HCS12 features and the monitor will still function with security
enabled, it is recommended that a BDM pod be used for development of secure
systems.
The monitor as written creates an operating frequency of 24 MHz. If crystal
frequencies other than 4, 8, or 16 MHz are used, the user is responsible for
creating definitions for these crystals and verifying that the SCI communication
rate is within the ±4% tolerance allowed by the RS-232 standard. The oscillator
definitions are stored in the S12SerMonxrx.def file.
The monitor as written creates a hard reset function by using the COP
watchdog timer. It does so by enabling the COP and waiting for a COP timeout
reset to occur.
Freescale Semiconductor, Inc.
For More Information On This Product,
Serial Monitor Program for HCS12 MCUs
Go to: www.freescale.com
MOTOROLA