3. Hardware Features
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The microcontroller’s XFC pin is connected to an appropriate loop filter circuitry in order
to provide PLL stability at an internal bus frequency of 24 MHz.
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All microcontroller’s pins are available on the four connectors placed around the
microcontroller.
USB to BDM Interface
This section contains the circuitry needed to electrically and logically translate BDM-like
commands sent by the host PC through the USB cable to the BDM interface of the
microcontroller.
The USB interface is based on a Motorola MC68HC908JB16 microcontroller, which features
an on-board, low-speed USB peripheral.
The USB bus provides the power supply for the board. To protect the USB bus against short
circuits that may occur during experiments, the power supply circuitry features a 200 mA
auto-restore fuse.
Note:
even though USB specifications require low-speed devices to be used only with a
captive or manufacturer-specific USB cable, we have decided to use a standard USB cable.
We therefore recommend that you use the PK-HCS12E128 board with the USB cable
provided or, if you use another USB cable, ensure that the cable length does not exceed 2
meters.
Demo Section
The “Demo” section groups push-buttons, a potentiometer, and user LEDs. In detail:
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Eight user LEDs are connected to the microcontroller’s Port T pins. All of the
microcontroller I/O pins provide the required current to drive the low-current LEDs used
by the starter kit, so no external transistors are needed.
