I have an old 8051 board

https://www.amazon.in/Silicon-TechnoLabs-Development-P89V51RD2-SST89E516RD/dp/B014SIQ8SM



i connected board to PC with usb to rs232 cable. I have successfully programmed microcontroller P89V51RD2 on this board but it takes me too long to do this.

After I made more than 100 attempts, the microcontroller was successfully programmed once.

I changed the USB to RS232 converter also changed the, maxrs232 ic, cable and also tried changing the microcontroller i used Sst89e516rd2. I notice that the micro controller on the board is being programmed but after several attempts.

Now I don't understand further what exactly could be the problem and how can it be fixed

 

Bootloader usually waits some short time after reset before it starts user software on this MCU. During this short time it can accept request to load new user software, so you must catch this time after releasing onboard reset button and hitting to software upload button on your PC bootloader manager.

 

Should a Decoupling capacitor be added between VDD and ground pin of 8051 on the board?

 

If there is not any near the MCU then you better add one.

 

Does your controller have a boot loader already programmed into it?

The cheap USB to serial converters have I/O that is TTL compatible. Your serial interface looks like it is a real RS-232 to serial TTL adapter. I think you need a real FTDI USB to serial converter or equivalent sends data that swings positive and negative to talk to that RS-232 interface on your controller board.

 

Does your controller have a boot loader already programmed into it?

Yes

. I think you need a real FTDI USB to serial converter or equivalent sends data that swings positive and negative to talk to that RS-232 interface on your controller board.

I have tried with CP2102 chip is a single chip USB to UART bridge IC. But no luck
https://forum.allaboutcircuits.com/threads/some-doubts-about-8051-mcu.192787/

 

The 89s52 can be programmed either in "parallel mode" or "serial ISP" mode through the SPI port. Your board has an ISP connector for that, you will need and ISP dongle compatible to the PC software you are using.

A Bootloader, which can be used in newer chips, requires that the IC have "self programming" capabilities of the internal Flash. This way ,the (previously loaded with some other programming method) bootloader runs at startup and looks for a host PC, once a connection is established, the PC sends programming data (usually from an *.hex , intel hex file) to the bootloader, and it "self programs" ,that is, writes bytes within the same chip flash. Then, control is transferred from the bootloader software to the user program.

 

The 89s52 can be programmed either in "parallel mode" or "serial ISP" mode through the SPI port. Your board has an ISP connector for that, you will need and ISP dongle compatible to the PC software you are using.

I gave the 12 volt dc to the board. I removed both jumpers on JP4 to disconnect MAX232 from MCU.

I did the following connection.

1. CP2102's GND pin to the ground pin of ICSP.
2. CP2102's TXD pin to the RXD pin P3. 0 of Sst89e516rd2
3. CP2102's RXD pin to the TXD pin P3. 1 of Sst89e516rd2

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I went up to reset the switch steps but the microcontroller is not detected

 

ok. Checked that part and it seems to have a bootloader ROM built in.

It may be that you are having a power up sequence problem lock up. The CP2102 converter surely powers from the external USB 5V. Could you post a picture of the CP2102 converter you are using?

 

wouldn´t it be better to use a USB to RS232 converter so you keep your Max232?

 

The CP2102 also needs 5V (Vcc) to run. I assume the Vcc in that diagram is 5V, not something else?

 

wouldn´t it be better to use a USB to RS232 converter so you keep your Max232?

View attachment 291742

This is what I am saying in my first post. When I use USB to RS232 converter MCU is getting programmed once after many attempts. Program once after about 100 attempts.

 

Per @garce in post #10, the CP2102 is not compatible with the Max232. Signal voltages are different.