标题: 为何I2C 的连接数， 用400pF 限制？ [打印本页] 作者: Quantum_ 时间: 2017-11-24 20:26 标题: 为何I2C 的连接数， 用400pF 限制？ 1. 如题 ："The number of ICs that can be connected to the same bus is limited only by a maximum bus capacitance of 400 pF."---THE I2C-BUS SPECIFICATION g c+ C' Q7 s) T; t I2. 如何用电容来定义。 ! Z& b* B* S2 Q9 A+ f3. 这个400pF 是如何推导/计算 得来的？1 A. e- m- J" T; s
g) p6 W0 U. A8 \! V2 x谢谢！作者: 超級狗 时间: 2017-11-25 00:51 嗯插屁（NXP）I2C-Bus Specification and User Manual Revision 6.0 & r, X' v& O5 M2 XThe switched pull-up circuit in Figure 44 is for a supply voltage of VDD = 5 V ± 10 % and a maximum capacitive load of 400 pF. Since it is controlled by the bus levels, it needs no additional switching control signals. During the rising/falling edges, the bilateral switch in the HCT4066 switches pull-up resistor Rp2 on/off at bus levels between 0.8 V and 2.0 V. Combined resistors Rp1 and Rp2 can pull up the bus line within the maximum specified rise time (tr) of 300 ns. 0 {; S' f1 [# H0 S* u: H5 B" u% Z2 \( l/ K, {/ @" L9 ] 6 V- h! `: |% ^ ( M4 h+ m$ B& @, F4 p+ _: R
