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| 型号： | M68TC11E20B56 |
| 厂商： | 飞思卡尔半导体(中国)有限公司 |
| 英文描述： | HC11 Microcontrollers |
| 中文描述： | HC11微控制器 |
| 文件页数： | 207/242页 |
| 文件大小： | 1525K |
| 代理商： | M68TC11E20B56 |
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Driving Boot Mode from Another M68HC11
M68HC11 Bootstrap Mode, Rev. 1.1
Freescale Semiconductor
207
The duplicator program in EEPROM clears the DWOM control bit to change port D (thus, TxD) of U3 to
normal driven outputs. This configuration will prevent interference due to R9 when TxD from the target
MCU (U6) becomes active. Series resistor R9 demonstrates how TxD of U3 can drive RxD of U3[1] and
later TxD of U6 can drive RxD of U3 without a destructive conflict between the TxD output buffers.
As the target MCU (U6) leaves reset, its mode pins select bootstrap mode so the bootloader firmware
begins executing. A break is sent out the TxD pin of U6. At this time, the TxD pin of U3 is at a driven high
so R9 acts as a pullup resistor for TxD of the target MCU (U6). The break character sent from U6 is
received by U3 so the duplicator program that is running in the EEPROM of the master MCU knows that
the target MCU is ready to accept a bootloaded program.
The master MCU sends a leading $FF character to set the baud rate in the target MCU. Next, the master
MCU passes a 3-instruction program to the target MCU and pauses so the bootstrap program in the target
MCU will stop the loading process and jump to the start of the downloaded program. This sequence
demonstrates the variable-length download feature of the MC68HC711E9 bootloader.
The short program downloaded to the target MCU clears the DWOM bit to change its TxD pin to a normal
driven CMOS output and jumps to the EPROM programming utility in the bootstrap ROM of the target
MCU.
Note that the small downloaded program did not have to set up the SCI or initialize any parameters for
the EPROM programming process. The bootstrap software that ran prior to the loaded program left the
SCI turned on and configured in a way that was compatible with the SCI in the master MCU (the duplicator
program in the master MCU also did not have to set up the SCI for the same reason). The programming
time and starting address for EPROM programming in the target MCU were also set to default values by
the bootloader software before jumping to the start of the downloaded program.
Before the EPROM in the target MCU can be programmed, the V
PP
power supply must be available at
the XIRQ/V
PPE
pin of the target MCU. The duplicator program running in the master MCU monitors this
voltage (for presence or absence, not level) at PE7 through resistor divider R14–Rl5. The PE7 input was
chosen because the internal circuitry for port E pins can tolerate voltages slightly higher than V
DD
;
therefore, resistors R14 and R15 are less critical. No data to be programmed is passed to the target MCU
until the master MCU senses that V
PP
has been stable for about 200 ms.
When V
PP
is ready, the master MCU turns on the red LED (light-emitting diode) and begins passing data
to the target MCU.
EPROM Programming Utility
explains the activity as data is sent from the master MCU
to the target MCU and programmed into the EPROM of the target. The master MCU in the EVBU
corresponds to the HOST in the programming utility description and the "PROGRAM utility in MCU" is
running in the bootstrap ROM of the target MCU.
Each byte of data sent to the target is programmed and then the programmed location is read and sent
back to the master for verification. If any byte fails, the red and green LEDs are turned off, and the
programming operation is aborted. If the entire 12 Kbytes are programmed and verified successfully, the
red LED is turned off, and the green LED is turned on to indicate success. The programming of all 12
Kbytes takes about 30 seconds.
After a programming operation, the V
PP
switch (S2) should be turned off before the EVBU power is turned
off.
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