Download interface of STC microcontroller

I have been working on an STC download interface these days. I thought the circuit was simple and I thought it would be easy to make. But I spent a lot of effort to draw the PCB diagram, and I needed help from someone (I won't name him, he is very low-key). Finally, I finished drawing it and took it to Wudian to make the board. But the weather was not good. The printer of Wudian stopped working after printing a few sheets of paper. Fortunately, I printed one sheet out. The package basically met the requirements. There were a few that needed to be changed, and the line was too small. I enlarged it to 0.6MM, and it looked much better when it was printed. Later, I got the printer, but the last sheet was missing. Later, the printer just didn't work. I had no choice but to go home. The next day, I went back to Wudian. The printer was fine at first, but then it stopped working again. Later, I found that the paper had to be very good. Later, under the guidance of the Wudian people, I followed the steps step by step.

First check whether the packaging is correct. If it is correct, then print it on the wax paper.

The second step is to wrap the copper clad laminate with oil paper, and then use a machine to heat press it several times.

The third step is to use a solution to corrode the excess copper. The solution is also critical. If the concentration is low, you have to wait. Fortunately, it was just prepared and the concentration is relatively high. It only takes more than ten minutes.

The fourth step is to punch holes. It was my first time to punch holes, and I was really bad at it. It seems that I really failed the metalworking internship, and I violated the rules many times. Haha, fortunately I didn't use someone else's machine. After punching the holes, I checked the package. As soon as I checked it, I knew it was a tragedy. Those holes were too big, and the microcontroller couldn't fit. I made up my mind and used a large drill bit to drill the hole of the chip again, so that the chip could finally fit. The wiring should be larger next time, otherwise the pad will not be there next time when I punch the hole, which is more difficult to solder.

I started soldering right after I got home in the evening. The soldering went smoothly. Although my soldering skills are not that good, I am still okay at making things. I finished soldering at around 11 o'clock. Then I found that a resistor and a capacitor were missing. I removed the resistor directly from the previous circuit board. The capacitor was not working. I asked someone for one, but it looked different. Whatever, I just used one. Later, when debugging the circuit, it was really a tragedy. I found the problem as soon as I powered it on. The output level of the MAX232 could not reach 5V. Obviously, the chip was not working. Then I started to look for it from its power supply, and tested it one by one along the power supply to see if it was broken. Finally, I found that one of the wires was broken by me, so I soldered it. But only one pin of the MAX232 output level was correct, and the other pin was always not working. Later, I thought there might be something wrong with the circuit. Then I looked for the PDF of MAX232 and found that the polarity of two capacitors was different from that of our learning board. I still had a capacitor, so I removed it and replaced it with the same polarity as the PDF. I found that the data transmission indicator light was finally off, but it still didn't work. Later, I checked it, one by one, and found no broken wire. Finally, I turned my attention to the capacitor. I searched online and found that the capacitors on both sides of the crystal oscillator must be the same for it to work. I thought it might really be a capacitor problem. I was tired, and the computer might be tired too. The screen went blue several times, so I went to sleep.

The next day, I went to the production room in the college building to solder again. This time, I changed the capacitor, and then used the learning board to burn the program into the microcontroller, and then tested the microcontroller minimum system, and found that there was no problem with the microcontroller minimum system. This time, I was annoyed. What was going on? I really had an urge to get rid of everything and make a new one. Later, I calmed down. I read the PDF of MAX232 carefully and re-read the pins of the RS232 interface. Then I compared it with my circuit, and I sent it out without any mistakes. I thought, maybe the chip is broken. I changed my MAX232 to the learning board to burn the program, and there was no problem at all. Now, I have to find another way.

I think the problem should be with MAX232, so I wondered if the capacitor next to it was poorly soldered. I picked up the electric meter and tested all the capacitors that helped it work. Finally, I found that one leg of one capacitor was poorly soldered. I unsoldered the original leg and re-soldered it. I took it to the computer to burn it, and I was nervous. I pressed it, but there was still no response. I was depressed, it still didn't work. I took a closer look and found that I only connected the power cord and not the data cable. As soon as the data cable was connected, the two lights began to flash. Haha, the circuit worked, and I could finally eat. I saw that it was almost seven o'clock, so I quickly packed up and went to Nanyuan to eat some leftovers.

Below is the circuit diagram. Let's trust PDF. Sometimes other people's circuits may not be suitable for ours.

Note: Although this circuit is simple, I learned it by myself. I believe that a novice can also become an expert. This may make the experts embarrassed, so I hope you can give me some advice. But please use civilized language, otherwise, hehe~~.