GPIO中上拉电阻以及输出的低级别问题

只看该作者 · 2011-12-20 10:35

我在使用F28035 GPIO22 (已经设置为GPIO)，使用的是10K的上拉电阻（到3.3V）。当它执行“GpioDataRegs.GPASET.bit.GPIO22 = 1”
的时候并没有任何问题，但是当它执行到“GpioDataRegs.GPACLEAR.bit.GPIO22 = 1”的时候，我测试了GPIO22引脚，3.3V的高级别并
没有转换到低级别，只是紧紧停留在2.9V，问题是程序（代码）停留在“ESTOP0”。我只是对上拉电阻做了测试，除此之外没有其它的连接，有谁能帮我一下吧？

只看该作者 · 2012-1-8 01:09

If Read-Modify-Write operations are used on the GPxDAT registers, because of the delay between the
output and the input of the first instruction (I1), the second instruction (I2) will read the old value and
write it back.
GpioDataRegs.GPADAT.bit.GPIO1 = 1 ; I1 performs read-modify-write of GPADAT
GpioDataRegs.GPADAT.bit.GPIO2 = 1 ; I2 also a read-modify-write of GPADAT. ; It gets the old
value of GPIO1 due to the delay
The second instruction will wait for the first to finish its write due to the write-followed-by-read
protection on this peripheral frame. There will be some lag, however, between the write of (I1) and the
GPxDAT bit reflecting the new value (1) on the pin. During this lag, the second instruction will read the
old value of GPIO1 (0) and write it back along with the new value of GPIO2 (1). Therefore, GPIO1 pin
stays low.