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# _# D# M. _# a* V- l7 w2 a7 D& s2 f0 G
2. 如何用电容来定义。 9 D7 T+ n1 j" ?; ~3. 这个400pF 是如何推导/计算 得来的？ ; f6 [8 J# r. u! t4 `. l8 G1 p! _/ Q3 M& w: H3 |3 h: t4 v
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. m0 S6 [% G) J4 O8 g& ^
The 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. 9 P4 v* f8 t/ L / z: m) S) \7 y: h, B1 C G' h$ z; {! A; Z8 X
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