Hi! There is a Reference Design, the DRM039, for Single P...MC68HC908QT2CDW

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Hi! There is a Reference Design, the DRM039, for Single P...MC68HC908QT2CDW

Contributor I
There is a Reference Design, the DRM039, for Single Phase AC Inductuction Motor Control.
In the schematic file there is a MC68HC908QT2CDW microcontroller that, as I have understood well, can be programmed via a Bootloader header. This header uses only four pins: Vcc, GND, TX (PTA1), and RX (PTA2).
The microcontroller is soldered on the pcb. Also, I have one PE USB Multilink MON08 programmer.
Please help me to understand how to program this microcontroller.
I dont know what software application is needed from the Computer side.
I dont know how to connect my USB Multilink MON08 programmer to the microcontrollers four pins header.
Added p/n to subject

Message Edited by NLFSJ on 2008-10-17 02:03 PM
Message Edited by t.dowe on 2009-08-27 03:31 PM
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Specialist III
Hello DPIR, and welcome to the forum.
The circuit in question requires that unspecified boot loader firmware is resident on the chip in order to
erase and program the application firmware using a simple serial interface arrangement.  Without a
resident boot loader, you would need to use the USB Multilink.  Normally, this will require external
connection to all eight pins of the MCU, so that the Multilink may force the state at each port pin.  The
connection to some of the pins may be eliminated if they are held at the required state by the circuitry.
However, for in-circuit programming, the present circuit does not provide sufficient isolation for some of
the pins.  Assuming that you will wish to erase and re-program an already programmed device, the
programming connections would be as shown in Fig 9.3 of the datasheet.  The Multilink is capable of
supplying high voltage to PTA2, a clock signal to PTA5, using PTA0 for the data signal, and forcing the
other pins to their required state.
Here are the potential isolation issues -
  1. For the opto-coupled version of the circuit, the load on PTA0 is relatively high.  If too much for the
    Multilink, an isolating jumper may be required for the pin.
  2. PTA3 requires to be forced high - not possible if the switch is grounding the input.  A series
    isolating resistor would alleviate the problem.
  3. PTA4 requires to be forced low - problematic if the pot wiper is at Vdd.  Again, a series resistor
    would give independence from the wiper position.

Message Edited by bigmac on 2008-10-17 10:44 PM
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Contributor II
OK, let's see if I can make this understandable:
1) The HC908QT/QY MCUs has got a small ROM monitor inside. It is only good for programming new code into the Flash EPROM.
2) To make any kind of program development possible, a special piece of code is burned into the Flash EPROM area. It sits at the interrupt vector area and is erase/write protected.
3) This code makes it very nice to do program development, but as it sits on the interrupt vectors, you can't use them. Well no, you can use them by filling in a jump vector table at the end of  your user code.
This applies also to the reset vector.
4) If you buy a HC908QT/QY device, this piece of "Monitor" code has to be loaded first.
If you buy a dev. board which has a HC908QT/QY on it, I would assume that this is already burned into the Flash EPROM.
To read more about it, get the AN2305 from
5) The nice thing with this program, is that no extra pins are wasted. You don't have to worry about +9 V to the /IRQ pin and that kind of stuff. You only have to use the PTA0 pin for communication.
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