How does the ISP code (UART interface) provided by Nuvoton determine whether an ISP update procedure is required after b

[a_ziliu]

The ISP code (UART interface) provided by Nuvoton can determine whether an ISP update is required through software. The ISP update will be started if a command is received within the set time.

Developers generally leave an updated path on the product, but whether an ISP update is required will be determined by software or hardware.
(1) Hardware determination: It uses the extra I/O pin, through high logic and low logic as the reference for determining whether to perform an ISP update after booting. The advantage is that it takes almost no time to determine it and the disadvantage is that an I/O pin will be occupied.
(2) Software determination: The device first recognizes and communicates with the PC through USB and determines whether an ISP update is required. The advantage is that no additional hardware cost is required and the disadvantage is that USB identification will take a while.

Usually, when UART is used as the interface for ISP update, software determination will be used to save hardware costs. Since the time taken by the UART to receive the command is very short. Assuming that the UART's baud rate is 115200, the command length is 8 bits and only takes 0.00008681 seconds. If the command is not received within the set time (time-out), the ISP update will not be performed. Compared with USB recognition that takes a few seconds, the way UART uses software to determine whether to perform an ISP update is more cost-effective.