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???
10/16/10 21:05
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 		 #179136 - Lets Read That Again
Responding to: ???'s previous message
Justin Fontes said:
First off, you are referring to:

http://www.atmel.com/dyn/produ...rt_id=3960

which will give you the errata and other important documents. Looking within the datasheet on page 32 at the top
ATMEL Datasheet said:
The Hardware conditions (EA = 1, PSEN = 0) during the Reset falling edge force the on-chip bootloader execution.


According to your sequence you're pulling PSEN low too late. I figured you would be able to program this device if it came directly from the manufacture as they usually leave most of their devices in a bootloader state, but maybe this chip is special?


As far as I can tell the sequence specified by Mahesh sounds like it is correct. Remember this MCU has a reset that is high active for the RESET state. So the requirement as specified by Atmel in the data sheet:

    "... (EA = 1, PSEN = 0) during the Reset falling edge ..."

correspond to what Mahesh published as:

    1. pin EA is tied to Vcc.
    2. While chip is in RESET condition, we are making PSEN low.
    3. then RESET is removed.

There is a small possibility of a contention upset going on with the PSEN signal after RESET however. The PSEN signal is normally an output from the MCU and holding it low for seconds after RESET's falling edge could lead to stress of that output and possible upset of the chip. Atmel even makes an important statement about this in their document at (click):

Save This Code
Two important points must be remembered when using 
the PSEN for forcing entry into the bootloader:

   (a)   THE PSEN MUST NOT BE TIED PERMANENTLY TO 
         GROUND !  Neglecting this can cause the device 
         to become unresponsive as it is important 
         that the PSEN be free to toggle at power-on !

   (b)   THE PSEN IS NORMALLY AN OUTPUT SO USE A PULLDOWN 
         RESISTOR e.g. 1k ohm.

Neglecting this could possibly damage the device and will 
provoke superior current consumption than normal.


Michael Karas







List of 10 messages in thread
TopicAuthorDate
Problem related to programing AT89c51RE2            01/01/70 00:00      
   Maybe a problem with your sequence            01/01/70 00:00      
      Lets Read That Again            01/01/70 00:00      
         You normally hold PSEN and then RESET            01/01/70 00:00      
         I knew about the 1k...            01/01/70 00:00      
   psen low, rst high before power applied            01/01/70 00:00      
      just curious            01/01/70 00:00      
         my mistake            01/01/70 00:00      
   Problem still is persisting            01/01/70 00:00      
      I only use Atmel for 8051            01/01/70 00:00      

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