參數(shù)資料
型號: AN2104
廠商: 飛思卡爾半導(dǎo)體(中國)有限公司
英文描述: Using Background Debug Mode for the M68HC12 Family
中文描述: 使用的M68HC12家庭背景調(diào)試模式
文件頁數(shù): 3/20頁
文件大小: 414K
代理商: AN2104
Application Note
Theory of Operation
AN2104
3
Figure 2. BDM Tool Connector
TocommunicatewiththeBDMonthepart,twopinsareused:BKGDand
GND. This method of serial interface is used to both send and receive
data. A special communications protocol is used that resynchronizes at
the beginning of each bit. By doing this, a greater frequency tolerance
for synchronization is allowed.
All bits are started with a falling edge signal that is initiated by the
external host. After the MCU sees this falling edge, it waits nine E-clock
cycles and then samples the level on the BKGD pin. The data is
transferred MSB (most significant bit) first at the rateof 16 E-clock cycles
per bit. The E-clock is defined as the SYSCLK divided by two.
The two types of BDM commands are:
Hardware
Firmware
When using hardware commands, the BDM is enabled, but not active,
and the user’s code is running. See
Table 1
. These commands allow all
internal and external memory, which is accessible to the microcontroller,
to be read or written. This also includes on-chip I/O (input/output) and
control registers.
The control logic watches the bus for any free bus cycles that it can use
to execute the hardware command. By using the free bus cycles, the
CPU is not disturbed. If, however, a free cycle is not found within a
specified time, it will use a bus cycle, which temporarily freezes the CPU.
2
4
6
5
3
1
RESET
BKGD
V
DD
GND
V
FP
NC
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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