Mon08 and MC908QT4

[iagane]

I am a new user to the forum

I bought MC908QT4 and MC908QY2 and I builded a circuit with a MAX232 + 74125 + 908QT4

I connected the rs232 of my computer to the board and I  loaded  the Metrowerks debugger.

I tried to connect to my 8\908QT4 but I have got no anwser from thje 908QT4.

My computer use only 3 wires - RX, TX and GND.

The 908QT4 is connected like that: PTA0 to 74125, PTA2 to GND on Power UP

With the Oscilloscope, I have got signal on the pin PTA0 but the 908QT4 does not seem to reply to the computer.

I have made something wrong and What I have to do to get in touch with the 908QT4

thanks

[peg]

Hello and welcome to the fora, iagane.

The connection you have made will only gain access to a blank device.

This device may have had an internal oscillator trim value programmed into $FFC0

This causes the blank check to fail which means you need to do a high voltage on IRQ type entry.

You will need this circuit later anyway so you may as well build it now.

This needs an external 9.8MHz clock on OSC1

9V on IRQ

RST and A1 high

A4 low

See the drawings in the Development Support chapter.

Good Luck!