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I2C 規範上的說明︰/ s7 s$ X+ {3 D% C- [! O4 x
7 F. n/ a. P5 ]$ G( t" vRp min is shown in Fig.37. The required noise mrgin of 0.1VDD for the LOW level, limits the maximum value of Rs. Rs max as a function of Rp is shown in Fig.38. The bus capacitance is the total capacitance of wire, connections and pins. This capacitance limits the maximum value of Rp due to the specified rise time. Fig.39 shows Rp max as a function of bus capacitance. The maximum HIGH level input current of each input/output connection has a specified maximum value of 10 mA. Due to the required noise margin of 0.2 VDD for the HIGH level, this input current limits the maximum value of Rp. This limit depends on VDD. The total HIGH level input current is shown as a function of Rp max in Fig.40.- W& Y3 t& V# V' B( i: X5 N2 O5 Z
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Series resistors Rs are optional. They protect the I/O stages of the I2C-bus devices from high-voltage spikes on the bus lines, and minimize crosstalk and undershoot of the bus line signals. The maximum value of Rs is determined by the maximum permitted voltage drop across this resistor when the bus line is switched to the LOW level in order to switch off Rp2.& _5 N6 b2 m$ ` K6 M) s. C0 x
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发表于 2013-11-6 20:48
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发表于 2014-2-7 17:34
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