89c51 does not run

Thread Starter

aamirali

Joined Feb 2, 2012
412
I am trying to run 89c51 it does not seem to start, as my test code is to toggle port in while(1) loop.

1. I had checked reset pin on scope its low.

2. I put cr0 probe on 10x.
Then I put probe on XTAL1, I don't see anything
I think crystal is not running.
I had changed crystal/mcu also but no change in behaviour.


Edit; I am usinh 15Mhz crystal with 30pf load cal
 
Last edited:

Thread Starter

aamirali

Joined Feb 2, 2012
412
1. I checked the pin reset on CRo, it stays low.

2. Didn't check PSEN & EA by scope. But they are left unconnected i.e. floating.
BTW what shoukd be voltage across them if I probe them.

3. probed ALE pin also nothing byt some noise
 

Thread Starter

aamirali

Joined Feb 2, 2012
412
I typed incorrectly.

EA is connected to +5V & ALE & PSEN are floating.
I don't see anything on crystals when I probe them with 10x cro probe.
Checked low on reset with CRO & high on EA.

What could be problem.
Should I ground the crystal body also
 

Thread Starter

aamirali

Joined Feb 2, 2012
412
I had checked on :
1. ALE pin shows osc/6 freq i.e for 15Mhz it outputs 2.5Mhz.

2. But PSEN also outputting same freq (approx.).
I don't know why. It should be high. My EA is permanently high. I had checked on CRO
 

Thread Starter

aamirali

Joined Feb 2, 2012
412
any help on that:


1. I have probed EA pin on CRo, its +5V constantly

2. Made a program to toggle port that's it.
void main
{
while(1)
{
P1 = ~P1;
}
}



3. Program made in keil,
Option checked in keil options: for using on chip rom only.



4. One thing I don't understand on PSEn pin I saw same frequency as on ALE pin.
I had checked for shrting, any coupling nearby but found none
 
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