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PCBA online programming, as the name suggests, burns the chip directly on the PCBA circuit board. It does not depend on the programming socket and is not affected by the life of the programming socket. It is a low-cost IC programming method. The PCBA circuit board of each product is various, there are many uncertain factors, which will bring abnormal conditions to online programming. The author analyzes several typical situations encountered recently to find the key points of the problem.
1. A dedicated external watchdog sometimes does bad things
The external hardware watchdog is widely used in electronic products. If the watchdog count is not cleared in time, the watchdog will generate a reset signal to reset the target chip to prevent the chip program from running away or entering an infinite loop. This effectively guarantees the stable operation of the system, but for chip PCBA programming, this is simply a nightmare.
When programming, the programmer cannot clear the external watchdog chip counter, causing the watchdog count to overflow and generate a reset signal, and reset the target chip, which will unexpectedly interrupt the programming of the current chip and cause the programming to fail. To prevent this kind of phenomenon, when designing the circuit, the hardware personnel should leave an interface that can disable the watchdog. Through this interface, first disable the watchdog, and then perform the PCBA programming work to prevent the chip from being watchdog accidentally. Reset, causing PCBA programming failure.
2. After burning the program correctly, the chip program does not run
Some electronic products have built-in batteries, especially smart bracelets, smart watches, smart phones and other products that are very popular now. After the programmer burns the code of the target board, the chip needs to be reset to run the code inside. In general PCBA factory assembly line production, after the target board is burned, it then enters the test link. Non-battery-powered boards will be re-powered during the test, and the chip will automatically power-on reset and run, and the code can run normally; for devices with batteries, since the battery is always powered, there is no power-on reset link, and the chip code cannot run, Resulting in failure of the subsequent test link.
In response to this situation, P800-ISP has added reset actions (including software reset and reset pin reset). In the combined operation, after the chip code is erased and programmed and verified, run the [Reset] action, so that these devices with batteries can be reset and started to work for subsequent product testing.
3. The influence of cable length, speed and stability on PCBA online programming
The communication quality between the programmer and the target board is related to the length of the communication cable and the communication speed. The longer the cable, the higher the communication speed, which will reduce the communication quality and affect the programming stability. In order for the PCBA programming work to be fast and stable, it is necessary to select the line length suitable for the target board according to the specific situation, and set the appropriate communication rate according to the line length.
4. The impact of power supply problems on PCBA online programming
The online programmer can generally supply power to the target board, but the power supply capacity is limited. For the target board with particularly large power consumption, as shown in the figure below, if the programmer is powered by the programmer, the programmer will be powerless, and then it needs to be powered directly from the outside; there is also a situation where the target board consumes a small amount of power, but it has a lot of power. The capacitor, the moment the programmer starts to supply power to the target board, will generate an instantaneous super charging current, that is, the surge effect, which will easily trigger the programmer's overcurrent protection. At this time, the target board is best to use external power supply. In view of this situation, P800-ISP adopts an innovative power supply mechanism and over-current detection algorithm, which effectively reduces the probability of over-current protection caused by the surge effect.
5. Summary of PCBA online burning work
The above points are often considered in the PCBA online programming work. In order to make the online programming production work stable, fast and orderly, it is necessary to take effective measures according to the specific conditions of each board to avoid abnormal situations., Improve programming efficiency.
