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01/11/12 12:02
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#185434 - AT89ISP Reset Pin Issue
Hi guys. I've been having LOTS of fun playing with the AT89S8253. I come from a PIC microcontroller background so changing over to MCS-51 was a bit of a chore but I seem to be grasping how to make the chip do everything I could make a PIC do.

However, I seem to be having an issue with my programmer hardware. I have the Atmel AT89ISP cable (not home made...purchased from Atmel). I'm not EXACTLY sure how the reset pin is supposed to work but I'm thinking that the reset pin SHOULD pull MCLR on the chip high during programming, then pull it low after the programming phase.

I'm using a 4.7K resistor on MCLR and I've tried it both as a pull up as well as a pull down and the reset pin doesn't seem to be doing what I THINK it should be doing. Even with my Fluke 189 I monitor the voltage on RST and it never seems to change from being high (5V). I've been manually connecting/disconnecting this wire to switch between program and run modes via using an alligator clip jumper between RST on the programmer and MCLR on the chip.

Can anyone advise me on this issue? Or is it even an issue at all?

List of 7 messages in thread
AT89ISP Reset Pin Issue      Jon Wilder      01/11/12 12:02      
   If you want a positive-going RESET ...      Richard Erlacher      01/11/12 13:10      
      no, you can't        Erik Malund      01/11/12 13:21      
         You can do it, though you may not want to      Richard Erlacher      01/11/12 23:35      
   The AT89ISP will expect active-high RESET      David Prentice      01/11/12 13:11      
   Try to run the initialize target command...      Kai Klaas      01/11/12 17:13      
      By the way...      Kai Klaas      01/12/12 07:57      

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