MC68HC908QY4A_10 Datasheet, PDF (196/200 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

A.3 Conversion Considerations
Enhancements lead to slight differences in operation from QYx Classic to the QYxA. There are a few
points that should be considered in the conversion process.
• The Monitor ROM changed from 2 K to 1 K in size. This has led to the limitation that programming
across page boundaries is no longer supported by the on-chip program range routine. Also, in very
rare cases, ROM code improvements could cause customers to have to modify a few instructions
in their application code. For example, when performing a mass erase, a valid address is required
instead of an unspecified address.
• The QYxA contains new modules like the 10-bit ADC and OSC. In rare cases, new modules could
cause customers to have to modify a few instructions in their application code. For example, if ADC
code was written so that entire registers are configured without respect to reserve bits, then the
ADC code will need to be revised to work correctly on the QYxA.
• The Reference Clock for ADC conversions has changed from the bus clock to the system clock
(Bus Clock * 4). A change to the divide register may be necessary to set the reference clock to a
specified value.
A.4 Code Changes Checklist
Below is a checklist that should be reviewed in the conversion process. This checklist will point out all the
issues that should be addressed as your code is ported.
1. Does the original software use Auxiliary ROM routines (for example, Getbyte, Putbyte, delnus)?
If so, the software will have to be changed to handle new Auxiliary ROM routines, addresses of
these routines have changed in QYxA. Code will have to be changed to use the proper addresses.
2. Does the software use FLASH as EEPROM?
If so, there are several possible issues for the page erase and mass erase routine. Software will
have to be checked to ensure that proper procedure is used and the CTRLBYT is set with a MOV
instruction not a BSET. Also, on-chip FLASH programming routines can no longer program across
row boundaries
3. Does the code use the auto wake up timer and does the application depend on the typical auto
wake time out?
Since the timeout has been improved for QYxA it may be necessary to modify software to
compensate for the change in timeout.
4. Bits changed in the OSCSC, CONFIG2, and ADC registers?
Any code that writes to these registers should be reviewed to ensure that the writes are not
affecting the changed bits
5. Does the code use external OSC, crystal, or RC?
If so, since the OSCOPT bits have changed locations code will have to be updated to update these
bits in their proper locations.
6. Does the code use the ADC?
If so, because on QYxA the ADC clock is driven from 4XBUSCLK instead of BUSCLK changes to
the ADC clock divider bits may be needed to maintain proper operation.
MC68HC908QYA/QTA Family Data Sheet, Rev. 3
196
Freescale Semiconductor