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???
05/25/05 12:16
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#93884 - PSEN
Responding to: ???'s previous message
hi,

Jan Waclawek said:
PSEN is less of a problem as it is of the open-drain type and it won't pull down unless external cycle occurs.


No, PSEN is not open-drain. At least for Atmel devices this pin is specified as:
=============================================================
At Reset:

 While the RST pin is high, ALE and PSEN are weakly pulled high.
 After RST is pulled low, it will take 1 to 2 machine
 cycles for ALE and PSEN to start clocking.

 Driving the ALE and PSEN pins to 0 while reset is active
 could cause the device to go into an indeterminate state.

At ONCE mode

 While the device is in ONCE mode, the Port 0 pins go into a
 float state, and the other port pins and ALE and PSEN
 are weakly pulled high.

At normal mode
 As PSEN is a an output port in normal operating mode
 after reset, user application should take care
 to release PSEN after falling edge of reset signal.
=============================================================

As /PSEN is specified to drive /OE of external program memory so this pin has true push-pull output. For example, looking at DC Parameters of AT89C51RD2, we may see that for /PSEN pin the output current is specified upto ±7mA. So this pin is not open-drain definely.

Regards,
Oleg

List of 30 messages in thread
TopicAuthorDate
Free PSEN/EA            01/01/70 00:00      
   Need 2 extra I/O?            01/01/70 00:00      
   Break            01/01/70 00:00      
      Just like disabling ALE            01/01/70 00:00      
         EA is a problem; PSEN - I don't know            01/01/70 00:00      
            Undocumented features            01/01/70 00:00      
               this is a weak argument            01/01/70 00:00      
            PSEN            01/01/70 00:00      
               PSEN II.            01/01/70 00:00      
                  PSEN III.            01/01/70 00:00      
            More I/O            01/01/70 00:00      
               I don't think that was Payam's point            01/01/70 00:00      
   the never ending request            01/01/70 00:00      
      ;-)            01/01/70 00:00      
   You can use ALE            01/01/70 00:00      
      Filter?            01/01/70 00:00      
         I assume ..            01/01/70 00:00      
            dirty hack...            01/01/70 00:00      
               why hack            01/01/70 00:00      
                  extra IO            01/01/70 00:00      
                     design and nothing else            01/01/70 00:00      
                        $1 in parts is not equal to $1 cost            01/01/70 00:00      
                        Oh yes, I AM still designing.            01/01/70 00:00      
                           stop whining            01/01/70 00:00      
                              it's just an illustration...            01/01/70 00:00      
                                 where does market size come in            01/01/70 00:00      
         that was said FITER not the FILTER            01/01/70 00:00      
            Sorry was a mistake it sohld be FILTER            01/01/70 00:00      
      Filter?            01/01/70 00:00      
   The illusion            01/01/70 00:00      

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