Problem with ISP header and AT89S52

[prodigyaj]

hello ,

i am using AT89s52

we had designed a PCB with an isp circuit ( the asim khan ) , the program burns into the uC fine but gives unexpected output.
Now we have a custom made board , when the same uC programmd from PCB is put in this board the program works fine .

So basically the situation is that the PCB that should have been a complete package of ISP and testing is only acting as a ISP giving erronous outputs ( basically the output is P0= 0 and all other porrts high ) while putiting in another board it works fine ...

can any1 out there help me out of this ... its really urgent as i hv a important project with this on saturday

 

[reflectarray]

Problem with uC!

I think there is must be a mistake with your ISP header on your PCB.
You should check this one:
http://www.atmel.com/dyn/resources/prod_documents/isp_C_v5.PDF

FYI:
TCK --> SCK
TDO --> MISO
TMS --> RST
TDI --> MOSI

 

[abidr]

Re: Problem with uC!

I think there is must be a mistake with your ISP header on your PCB

Agreed, have a look at the data sheet of the AVR and confirm that you PCB has same pinouts.
My guess is that there is some wrong connection on the ISP.

 

[prodigyaj]

Problem with uC!

well thank you guys ... i think i just found out the mistake
Pin no. 31 (EA) had to be connected to Vcc for accessing internal memory of the uC AT89s52.
However i would like to know one more thing that what exactly is the use of PULL up resistors in AT89s52 especially in Port 0 where the datasheet clearly states that the port 0 has no internal pull up resistance !

 

[deepu_ttc]

Re: Problem with uC!

hello friend as u know that in MCUs the ports are FETs working as switch for that drain should be connected to Vcc source to GND . as u see in port 0 schmatic the drain is no where connected i.e, to Vcc so we are connecting drain to Vcc using resistor this is called puu up resistor

 

[reflectarray]

Re: Problem with uC!

However i would like to know one more thing that what exactly is the use of PULL up resistors in AT89s52 especially in Port 0 where the datasheet clearly states that the port 0 has no internal pull up resistance !

Of course as there is no internal pull up in port0, you should add it externally.

 

[~E3016~]

Re: Problem with uC!

if you want to use port 0 as well as the other port, you HAVE TO connect to the pull up resistor, say about 4K7 or 10K, here is the schematic for asim khan