MC68HC11E0CFNE3 Datasheet, PDF (221/242 Pages) Freescale Semiconductor, Inc – M68HC11E Family

Boot ROM Variations
Bootloading a Program to Performa ROM Checksum
The bootloader ROM must be turned off before performing the checksum program. To remove the boot
ROM from the memory map, clear the RBOOT bit in the HPRIO register. This is normally a write-protected
bit that is 0, but in bootstrap mode it is reset to 1 and can be written. If the boot ROM is not disabled, the
checksum routine will read the contents of the boot ROM rather than the user’s mask ROM or EPROM at
the same addresses.
Inherent Delays Caused by Double Buffering of SCI Data
This problem is troublesome in cases where one MCU is bootloading to another MCU.
Because of transmitter double buffering, there may be one character in the serial shifter as a new
character is written into the transmit data register. In cases such as downloading in which this 2-character
pipeline is kept full, a 2-character time delay occurs between when a character is written to the transmit
data register and when that character finishes transmitting. A little more than one more character time
delay occurs between the target MCU receiving the character and echoing it back. If the master MCU
waits for the echo of each downloaded character before sending the next one, the download process
takes about twice as long as it would if transmission is treated as a separate process or if verify data is
ignored.
Boot ROM Variations
Different versions of the M68HC11 have different versions of the bootstrap ROM program. Table 3
summarizes the features of the boot ROMs in 16 members of the M68HC11 Family.
The boot ROMs for the MC68HC11F1, the MC68HC711K4, and the MC68HC11K4 allow additional
choices of baud rates for bootloader communications. For the three new baud rates, the first character
used to determine the baud rate is not $FF as it was in earlier M68HC11s. The intercharacter delay that
terminates the variable-length download is also different for these new baud rates. Table 3 shows the
synchronization characters, delay times, and baud rates as they relate to E-clock frequency.
Commented Boot ROM Listing
Listing 3. MC68HC711E9 Bootloader ROM contains a complete commented listing of the boot ROM
program in the MC68HC711E9 version of the M68HC11. Other versions can be found in Appendix B of
the M68HC11 Reference Manual.
Table 3. Bootloader Baud Rates
Sync
Character
Timeout
Delay
Baud Rates at E Clock =
2 MHz 2.1 MHz 3 MHz 3.15 MHz 4 MHz 4.2 MHz
$FF
4 characters 7812 8192 11,718 12,288 15,624 16,838
$FF
4 characters 1200 1260 1800 1890 2400 2520
$F0 4.9 characters 9600 10,080 14,400 15,120 19,200 20,160
$FD 17.3 characters 5208 5461 7812 8192 10,416 10,922
$FD 13 characters 3906 4096 5859 6144 7812 8192
M68HC11 Bootstrap Mode, Rev. 1.1
Freescale Semiconductor
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