ADS1248怎么测不到内部参考电压

对寄存器可读可写 可是配置完02这个地址的时（写0x30）在vrefout测不到2.048v，测的值不定然后开始减小直到为0，不知道怎么回事？

数据手册上:  INTERNAL VOLTAGE REFERENCE 说到

The onboard reference is controlled by the registers;by default, it is off after startup (see the ADS1247/48 Detailed Register Definitions section for more details).Therefore, the internal reference must first be turned on and then connected via the internal reference multiplexer. Because the onboard reference is used to generate the current reference for the excitation current sources, it must be turned on before the excitation currents become available.

是不是应该先打开, 再启用, 中间要等待稳定的过程?

怎么打开和启动，有什么命令？不是直接上电就打开了么？

没有看到有打开和启用的命令？