AN2295 Freescale Semiconductor / Motorola, AN2295 Datasheet - Page 4

• Manufacturer Part Number: AN2295
• Description: Developers Serial Bootloader for M68HC08 and HCS08 MCUs
• Manufacturer: Freescale Semiconductor / Motorola

FC Protocol Description
Initial Hook-Up
There are several methods to enter bootloader mode. Several other solutions use a “ certain level on
certain pin” method. An example of this method is: If logic 0 appears on an IRQ pin during MCU startup,
the bootloader code starts. Otherwise, the user code starts.
Because the developer’s serial bootloader application must use the lowest number of pins, a “ certain
character at a certain time” method is used. This means that the MCU sends out an ACK character
through the serial interface and waits for an answer. If no character is received within the specified time
(hook-up time-out), the process continues with the user code.
If this becomes a limitation for any reason, the user may modify the bootloader code to meet the
application needs; for example, an additional simple IRQ pin test at startup can be implemented). See
more in
Clock Source
FC protocol allows two scenarios, depending on whether the MCU runs on a known and exact frequency
or uses an RC (resistor, capacitor) clock or internal clock (or any clock which is not known at compile
time).
Unknown MCU Communication Speed
If the frequency is uncertain (not known at compile time), the MCU will not check whether an incoming
ACK character conforms only to the $FC pattern. Because of the MCU clock tolerance, several characters
can be interpreted differently instead of the original $FC sent out by the PC as shown in
$FC pattern check on the MCU side can be eliminated completely, which saves MCU memory.
4
POWER-ON
M68HC08 System
QUIT
Figure 2. Simplified Flow Diagram of the Bootloader Application
RESET
Developer’s Serial Bootloader for M68HC08 and HCS08 MCUs, Rev. 6
Limitations.
COMMANDS
COMMUNICATION
HOOK-UP
CALIBRATION
READ
TIME-OUT
RESET SOURCE
TEST
WRITE
ERASE
Freescale Semiconductor
IDENT
Figure
USER
CODE
3. The