比如31XC系列内部高速技数器要利用计数 SFB COUNT (SFB 47)其它如频率测量 SFB FREQUENC (SFB 48)，脉宽调制 SFB PULSE (SFB 49）等都不能正确执行。手册中有一段：
Note that SFB12, SFB13, SFB14, SFB15, SFB16, SFB19, SFB20, SFB21, SFB22,
SFB23, SFB41, SFB42, SFB43, SFB44, SFB46, SFB47, SFB48, SFB49, SFB60,
SFB61, SFB62, SFB63, SFB64, and SFB65 are NOPs (do not perform any
operation).
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