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Jim Granville
01/17/13 12:59
Read: 913 times

#189229 - Clarifies
Responding to: Koen De Ganck's previous message
Koen De Ganck said:

So, for future designs of upgrades, it could be a good idea to place a pull up.

I think only if you have external (pull down?) loads on PSEN ?

A PSEN normally not connected, will not be pulled low.
I measured -27uA on a gnded pin, and -225uA on ~1.85V, so it is a QuasiIO pin, during RST active. After reset exit, it has a strong pullup (-18mA)

Boot mode is entered if PSEN is seen to be low on RST de-assert.

Koen De Ganck said:
I updated about 20 boards with a pull-up of 560K on pin 'PSEN'.
All but 1 board started up in a good way (10-20 tries), although most of them failed many times without pull-up.
The single board that had 1 failure out of 20, worked well with a pull-up of 330K.

While is it nice to know the boundary condition, I would fit well under 330K to allow for temperature and device margins.

Koen De Ganck said:

PSEN : is loaded with 1 port, the traces are within 2 x 3cm (4 endpoints ) on a multilayer.

What exactly is this load ?

Koen De Ganck said:

I also remove the LM810 reset chip as this is not needed anymore as the board works on 3V3.

I thought something else was driven by RST ?
I know a SW reset will drive out on RST pin, but I'm not sure if Power-Up does ?

List of 24 messages in thread
Reset issue with new Atmel AT89LP51ED2      Koen De Ganck      01/16/13 02:42      
   Do never use a ┬ÁC from which only a preliminary...      Kai Klaas      01/16/13 05:48      
      configuration settings      Koen De Ganck      01/16/13 05:59      
         what about negative reset?      Jan Waclawek      01/16/13 06:56      
            good idea but      Koen De Ganck      01/16/13 07:23      
   Some things to check...      Jim Granville      01/16/13 12:38      
      also try no LM810 at all      Jim Granville      01/16/13 13:02      
         reset is inverted      Koen De Ganck      01/16/13 13:30      
      no strange signals      Koen De Ganck      01/16/13 13:18      
         Extra modes ?      Jim Granville      01/16/13 16:30      
            pull-up on PSEN solves the problem      Koen De Ganck      01/17/13 03:01      
               small capacitor ?      Jim Granville      01/17/13 13:06      
                  small capacitor      Koen De Ganck      01/17/13 14:10      
   side-stepping the problem?      Jan Waclawek      01/17/13 01:34      
      SST could be an option      Koen De Ganck      01/17/13 03:08      
   final status AT89LP51ED2 reset      Koen De Ganck      01/17/13 07:43      
      Clarifies       Jim Granville      01/17/13 12:59      
         loads on PSEN      Koen De Ganck      01/17/13 14:06      
            An isolated PSEN works fine ?      Jim Granville      01/17/13 14:30      
               GAL causes problem      Koen De Ganck      01/17/13 15:41      
                  ATF16V8CZ has Pin-keeper      Jim Granville      01/17/13 16:02      
                     'Z' indeed      Koen De Ganck      01/17/13 16:35      
                        ATF16V8BQL has Icc of ~1.5mA      Jim Granville      01/17/13 16:54      
                           'BQL' version could be an option      Koen De Ganck      01/17/13 17:50      

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