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ISL81387 Datasheet(PDF) 13 Page - Intersil Corporation |
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ISL81387 Datasheet(HTML) 13 Page - Intersil Corporation |
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13 / 27 page  ISL81387, ISL41387 13 FN6201.4 June 9, 2014 Submit Document Feedback Detailed Description The ISL81387, ISL41387 port supports dual protocols: RS-485, RS-422, and RS-232. RS-485 and RS-422 are differential (balanced) data transmission standards for use in high speed (up to 20Mbps) networks, or long haul and noisy environments. The differential signalling, coupled with RS-485’s requirement for extended common mode range (CMR) of +12V to -7V make these transceivers extremely tolerant of ground potential differences, as well as voltages induced in the cable by external fields. Both of these effects are real concerns when communicating over the RS-485, RS-422 maximum distance of 4000’ (1220m). It is important to note that the ISL81387, ISL41387 don’t follow the RS-485 convention whereby the inverting I/O is labelled “B/Z”, and the non-inverting I/O is “A/Y”. Thus, in the following application diagrams, the ISL81387, ISL41387 A/Y (B/Z) pins connect to the B/Z (A/Y) pins of the generic RS-485, RS-422 ICs. RS-422 is typically a point-to-point (one driver talking to one receiver on a bus), or a point-to-multipoint (multidrop) standard that allows only one driver and up to 10 receivers on each bus. Because of the one driver per bus limitation, RS-422 networks use a two bus, full duplex structure for bidirectional communication, and the Rx inputs and Tx outputs (no tri-state required) connect to different busses, as shown in Figure 9. Tx and Rx enables aren’t required, so connect RXEN and DEN to VCC through a 1k resistor. Conversely, RS-485 is a true multipoint standard, which allows up to 32 devices (any combination of drivers- must be tri-statable - and receivers) on each bus. Now bidirectional communication takes place on a single bus, so the Rx inputs and Tx outputs of a port connect to the same bus lines, as shown in Figure 8. A port set to RS-485, RS-422 mode includes one Rx and one Tx. See application note AN1378 for details on implementing a three pin, selectable RS-232/ half duplex RS-485 port. RS-232 is a point-to-point, singled ended (signal voltages referenced to GND) communication protocol targeting fairly short (<150’, 46m) and low data rate (<1Mbps) applications. A port contains two transceivers (2 Tx and 2 Rx) in RS-232 mode. Protocol selection is handled via the 485/232 logic pin. FIGURE 8. TYPICAL HALF DUPLEX RS-485 NETWORK FIGURE 9. TYPICAL RS-422 NETWORK 0.1 F + D R VCC GND RA RXEN * DEN DY Y Z +5V RT 0.1µF + D R VCC GND RO RE DE DI A/Y B/Z +5V 0.1µF D VCC GND RO RE DE DI A/Y B/Z +5V R RT ISL81387, ISL41387 GENERIC 1/2 DUPLEX 485 XCVR GENERIC 1/2 DUPLEX 485 XCVR Tx/Rx *QFN ONLY, CONNECT RXEN TO GND A B 0.1 F + D R VCC GND RA DEN DY B A +5V 0.1 F + D R VCC GND RO DI A Z +5V 0.1 F VCC GND RO RE +5V R RT ISL81387 (MASTER) GENERIC 422 Rx (SLAVE) GENERIC FULL DUPLEX 422 XCVR (SLAVE) A B RT Y Z Y B 1k RXEN |
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