MC68HC711E20CFS2 MOTOROLA [Motorola, Inc], MC68HC711E20CFS2 Datasheet - Page 219

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

AN1060 — Rev. 1.0
MOTOROLA
M68HC11 Family members which have 256 bytes of RAM, the download
length is fixed at exactly 256 bytes plus the leading $FF character.
The intercharacter delay counter is started [8] by loading the delay
constant from TOC1 into the X index register. The 19-E-cycle wait loop
is executed repeatedly until either a character is received [9] or the
allowed intercharacter delay time expires [10]. For 7812 baud, the delay
constant is 10,241 E cycles (539 x 19 E cycles per loop). Four character
times at 7812 baud is 10,240 E cycles (baud prescale of 4 x baud divider
of 4 x 16 internal SCI clocks/bit time x 10 bit times/character x 4
character times). The delay from reset to the initial $FF character is not
critical since the delay counter is not started until after the first character
($FF) is received.
To terminate the bootloading sequence and jump to the start of RAM
without downloading any data to the on-chip RAM, simply send $FF and
nothing else. This feature is similar to the jump to EEPROM at [4] except
the $FF causes a jump to the start of RAM. This procedure requires that
the RAM has been loaded with a valid program since it would make no
sense to jump to a location in uninitialized memory.
After receiving a character, the downloaded byte is stored in RAM [11].
The data is transmitted back to the host [12] as an indication that the
download is progressing normally. At [13], the RAM pointer is
incremented to the next RAM address. If the RAM pointer has not
passed the end of RAM, the main download loop (from [7] to [14]) is
repeated.
When all data has been downloaded, the bootloader goes to [16]
because of an intercharacter delay timeout [10] or because the entire
512-byte RAM has been filled [15]. At [16], the X and Y index registers
are set up for calling the PROGRAM utility routine, which saves the user
from having to do this in a downloaded program. The PROGRAM utility
is fully explained in
bootloader program is to jump to the start of RAM [17], which starts the
user’s downloaded program.
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
EPROM Programming
Utility. The final step of the
Application Note
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