DAC8728必须要在cs信号为高的时候才输出么？说明文档40面里面说到 异步模式 When the correction engine is off (SCE bit = '0'), the DAC Data Registers and DAC latches are updated immediately when CS goes high. cs是片选信号，低有效，片选为高了，芯片都不工作了，怎么还输出？
还有个问题，文档里面说 Asynchronous Mode ：In this mode, the LDAC pin is set low at power-up. Synchronous Mode：To activate this mode, take LDAC low or set the LD bit to '1' after CS goes high. 我就设置LDAC一直低，那不矛盾么，到底是异步还是同步？
