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MCP1318MT bảng dữ liệu(PDF) 33 Page - Microchip Technology |
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MCP1318MT bảng dữ liệu(HTML) 33 Page - Microchip Technology |
33 / 44 page © 2005 Microchip Technology Inc. DS21985A-page 33 MCP131X/2X 5.7 Controllers and Processors With Bidirectional I/O Pins Some microcontrollers have bidirectional Reset pins. Depending on the current drive capability of the control- ler pin, an indeterminate logic level may result if there is a logic conflict. This can be avoided by adding a 4.7 k Ω resistor in series with the output of the MCP131X/2X (Figure 5-7). If there are other compo- nents in the system that require a Reset signal, they should be buffered so as not to load the Reset line. If the other components are required to follow the Reset I/O of the microcontroller, the buffer should be con- nected as shown with the solid line. FIGURE 5-7: Interfacing the MCP131X/2X Push-Pull outputs to a Bidirectional Reset I/O. 5.8 RESET Signal Integrity During Power-Down The MCP131X/2X Reset output is valid to VDD = 1.0V. Below this 1.0V, the output becomes an "open circuit" and does not sink or source current. This means CMOS logic inputs to the microcontroller will be floating at an undetermined voltage. Most digital systems are completely shut down well above this voltage. However, in situations where the Reset signal must be maintained valid to VDD = 0V, external circuitry is required. For devices where the Reset signal is active-low, a pull-down resistor must be connected from the MCP131X/2X Reset pin(s) to ground to discharge stray capacitances and hold the output low (Figure 5-8). Similarly for devices where the Reset signal is active-high, a pull-up resistor to VDD is required to ensure a valid high Reset signal for VDD below 1.0V. This resistor value, though not critical, should be chosen such that it does not appreciably load the Reset pin(s) under normal operation (100 k Ω will be suitable for most applications). FIGURE 5-8: Ensuring a valid active-low Reset pin output state as VDD approaches 0V. MCP13XX VDD RST GND MCLR GND Buffered Reset To Other System Components MCU 4.7 k Ω Buffer PICmicro® MCP13XX V DD V DD R1 100 k Ω RST GND |
Số phần tương tự - MCP1318MT |
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Mô tả tương tự - MCP1318MT |
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