P89C61X2 into ISP mode problem

[PatrickChiu]

I use "Flash Magic Application Note 1", Figure 1 to build my ISP Tool

and have some problem.

In "Flash Magic Application Note 1", tell me that when the com port is closed , RTS and DTR are at a RS232 voltage level below -3V.

But when I put every thing together and power on .

PSEN always Low, and RST alway high.

I found DTR, RTS on 0.7V

this is my circuit diagram

http://www.usync.tzo.com/fm_isp.pdf

PSEN pull up 10k , and  RST 10uF, 10k at other page.

This problem is confuse me serval day .

Have anyone can tell me how to do ? :-(

Thank you very much .

Patrick Chiu.

[Andy Ayre]

You will have to do some troubleshooting. Try disconnecting the RS232 cable from the board and measuring the DTR and RTS voltages on the pins. If they are below -3V then you will need to work out what the problem might be.

If you look at section 2.2 of the app note there are waveforms for various points in the circuit. If you use a scope to compare yours with the app notes, look to see where the differences are and then investigate further.

[PatrickChiu]

Hi I have a question ,

Does RS232 pin RTS, DTR need a MAX232 that convert to TTL voltage level?

Thanks.

Patrick Chiu

[PatrickChiu]

I found the answer , in previous topic ,


DTR RTS , need a MAX232  convert  to TTL voltage level .

Thanks, Andrew Ayre .

You are very kindly that answer my question.

^_^

Best Regards,
Patrick Chiu