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The signature 0x15, 0xC2, 0x82 is for the P89C51RD2xx. The P89C61X2 should have 0x15, 0xC2, 0xF0.

My guess is that you have an AC or DC requirement in your circuit that is marginal. It may work for one device but not another. In electronics things vary slightly, even different batches of the same device can behave differently when they are at the limits of the specification.

The best way to debug your circuit is with a scope. Check everything and make sure it meets the specification in the device data sheet.

Andy

Thank for your advice.

I eventually solve the problem after replace the MAX 232 due to some straight respone on reset..

and the probelm have solved..

Maybe it was just a probelm in IC.

Again, thanks for your help, andy. 

Oscar

Flash Magic is sending a 'U' and not getting an echo back from the device. Use a scope to check the 'U' is arriving at the RxD pin and a 'U' is being transmitted from the TxD pin.

Andy

Dear Andy

Thank for your advise.

I have not got a scope now, and i will try it tomorrow.

But something is confusing me, because I have check my circuit by digital multimeter to confirm the circuit is not blocked for serial communication for two times.

Moreover, the flash magic can detect the other device surprising, when I found a P89C61XBA (borrow from others) and put it on my same circuit.

I have got a screenshot which is the attach photo.

but a few problems appear:

(i) when I want to read the device, the flash magic warning me the model P89C61X2 is not correct.

(ii) I take the terminal test, both C61X2 and C51C51RD2Hxx doesn't not have echo.

so I am wondering why can detect some device (C61X2 only not C51RD2Hxx) but fail to read or terminal test?..

does my circuit work ?

I have no idea now...Please help....thanks...

Oscar

I have take a look of the app note and build the circuit to connect the device to com port

But I failed to communicate to the device (e.g. can't read the device signature)

the message can't connect with specified baud rate appear every time.

I have check the P26 & P27 was in high level (4.5V).

& ALE is 1.55V which is assumed to be floating,

which should be rearching the requirment show in AN461.

I have attached the debug file.

Would anyone can give me some help on it please?