关于TMS320F28335的电源

下面是28335 数据手册127页的说明。对于28335来说建议先上VDD，后上VDDIO。如果满足这个条件GPIO会是默认的输入状态。这时候如果有外部上拉或下拉

GPIO的电平会被拉倒相应的点平，如果外部没有上拉。要查GPIO Port x Pullup Disable (GPxPUD) Registers,看默认是不是内部上拉。

6.8 Power Sequencing

No requirements are placed on the power up/down sequence of the various power pins to ensure the
correct reset state for all the modules. However, if the 3.3-V transistors in the level shifting output buffers
of the I/O pins are powered prior to the 1.9-V transistors, it is possible for the output buffers to turn on,
causing a glitch to occur on the pin during power up. To avoid this behavior, power the VDD pins prior to or
simultaneously with the VDDIO pins, ensuring that the VDD pins have reached 0.7 V before the VDDIO pins
reach 0.7 V.