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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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HM3085 датащи(PDF) 8 Page - Shenzhen Huazhimei Semiconductor Co., Ltd |
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HM3085 датащи(HTML) 8 Page - Shenzhen Huazhimei Semiconductor Co., Ltd |
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8 / 12 page  Figure5. Receiver Propagation Delay Test Load Detailed Description The HM3085 high - speed transceiver for RS-485 communication contains one driver and one receiver. These devices feature fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled (see the Fail-Safe section). The HM3085 feature reduced slew-rate driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps (see the Reduced EMI and Reflections section). The HM3085 is a half-duplex transceiver. The voltage operates from a single +5V supply. Drivers are output short-circuit current limited. Thermal shutdown circuitry protects drivers against excessive power dissipation. When activated, the thermal shutdown circuitry places the driver outputs into a high impedance state. Receiver Input Filtering The receiver of the HM3085, when operating in 1Mbps, incorporates input filtering in addition to input hysteresis. This filtering enhances noise immunity with differential signals that have very slow rise and fall times. Receiver propagation delay increases by 25% due to this filtering. Fail-Safe The HM3085 guarantees a logic-high receiver output when the receiver inputs are shorted or open, or when they are connected to a terminated transmission line with all drivers disabled. This is done by setting the receiver threshold between -50mV and -200mV. If the input voltage of differential receiver (A-B) is greater than or equal to -50mV, RO is logic high. If A-B is less than or equal to -200mV, RO is logic low. In the case of a terminated bus with all transmitters disabled, the receiver differential input voltage is pulled to 0V by the termination. With the receiver threshold of the HM3085, this results in a logic high with a 50mV minimum noise margin. Unlike previous fail-safe devices, the -50mV to -200mV threshold complies with the +/-200mV EIA/TIA-485 standard. ESD Protection As with HM3085, ESD-protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The driver output and receiver input of the HM3085 has extra protection against static electricity. The ESD-protected pins are tested with reference to the ground pin in a powered-down condition. |
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