MC68HC12 MOTOROLA [Motorola, Inc], MC68HC12 Datasheet - Page 400

• Manufacturer Part Number: MC68HC12
• Description: The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit
• Manufacturer: MOTOROLA [Motorola, Inc]

Development Support
Technical Data
400
SPEEDUP PULSE
START OF BIT TIME
BKGD PIN
BKGD PIN
DRIVE TO
(TARGET
BDMCLK
TARGET MCU
HOST
DRIVE AND
MCU)
PERCEIVED
Figure 20-3. BDM Target to Host Serial Bit Timing (Logic 0)
Figure 20-2
MC68HC912DT128A MCU. Since the host is asynchronous to the target
MCU, there is a 0-to-1 cycle delay from the host-generated falling edge
on BKGD to the perceived start of the bit time in the target MCU. The
host holds the BKGD pin low long enough for the target to recognize it
(at least two target B cycles). The host must release the low drive before
the target MCU drives a brief active-high speed-up pulse seven cycles
after the perceived start of the bit time. The host should sample the bit
level about ten cycles after it started the bit time.
10 CYCLES
shows the host receiving a logic one from the target
Development Support
10 CYCLES
HIGH-IMPEDANCE
HOST SAMPLES
BKGD PIN
SPEEDUP PULSE
MC68HC912DT128A — Rev 4.0
HC12A4 BDM TARGET TO HOST TIM 0
EARLIEST
START OF
NEXT BIT
MOTOROLA