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SP3223EB датащи(PDF) 12 Page - Sipex Corporation |
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SP3223EB датащи(HTML) 12 Page - Sipex Corporation |
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12 / 23 page ![]() Date: 10/06/06 SP3223 +3.0V to +5.5V RS-232 Transceivers © Copyright 200 6 Sipex Corporation 12 The AUTO ON-LINE® circuit has two stages: 1) Inactive Detection 2) Accumulated Delay The first stage, shown in Figure 20, detects an inactive input. A logic HIGH is asserted on R XINACT if the cable is disconnected or the external transmitters are disabled. Otherwise, R XINACT will be at a logic LOW. This circuit is duplicated for each of the other receivers. The clock rate for the charge pump typically operates at above 250kHz. The external capaci- tors can be as low as 0.1 µF with a 16V break- down voltage rating. The second stage of the AUTO ON-LINE® circuitry, shown in Figure 21, processes all the receiver's R XINACT signals with an accumu- lated delay that disables the device to a 1 µA supply current. The STATUS pin goes to a logic LOW when the cable is disconnected, the external transmitters are disabled, or the SHUTDOWN pin is invoked. The typical accumulated delay is around 20 µs. When the SP3223 drivers or internal charge pump are disabled, the supply current is reduced to 1 µA. This can commonly occur in handheld Figure 16. AUTO ON-LINE® Timing Waveforms or portable applications where the RS-232 cable is disconnected or the RS-232 drivers of the connected peripheral are turned off. The AUTO ON-LINE® mode can be disabled by the SHUTDOWN pin. If this pin is a logic LOW, the AUTO ON-LINE® function will not operate regardless of the logic state of the ONLINE pin. Table 3 summarizes the logic of the AUTO ON-LINE® operating modes. The truth table logic of the SP3223 driver and receiver outputs can be found in Table 2. The STATUS pin outputs a logic LOW signal if the device is shutdown. This pin goes to a logic HIGH when the external transmitters are en- abled and the cable is connected. When the SP3223 devices are shut down, the charge pumps are turned off. V+ charge pump output decays to V CC,the V- output decays to GND. The decay time will depend on the size of capacitors used for the charge pump. Once in shutdown, the time required to exit the shut down state and have valid V+ and V- levels is typically 200 µs. For easy programming, the STATUS can be used to indicate DTR or a Ring Indicator signal. Tying ONLINE and SHUTDOWN together will bypass the AUTO ON-LINE® circuitry so this connection acts like a shutdown input pin RECEIVER RS-232 INPUT VOLTAGES STATUS +5V 0V -5V tSTSL tSTSH tONLINE VCC 0V DRIVER RS-232 OUTPUT VOLTAGES 0V +2.7V -2.7V S H U T D O W N |
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