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DS36C280TM Datasheet(PDF) 7 Page - National Semiconductor (TI) |
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DS36C280TM Datasheet(HTML) 7 Page - National Semiconductor (TI) |
7 / 9 page Typical Application Information TABLE 1. Device Pin Descriptions Pin # Name Description 1 RO Receiver Output: When DE/RE* (Receiver Enable) is LOW, the receiver is enabled (ON), if DO/RI ≥ DO*/RI* by 200 mV, RO will be HIGH. If DO/RI ≤ DO*/RI* by 200 mV, RO will be LOW. Additionally RO will be HIGH for OPEN (Non-terminated) inputs. 2 SR Slew Rate Control: A resistor connected to Ground controls the Driver Output rising and falling edge rates. 3 DE/RE* Combined Driver and Receiver Output Enable: When signal is LOW the receiver output is enabled and the driver outputs are in TRI-STATE (OFF). When signaI is HlGH, the receiver output is in TRI-STATE (OFF) and the driver outputs are enabled. 4 DI Driver Input: When DE/RE* is HlGH, the driver is enabled, if DI is LOW, then DO/RI will be LOW and DO*/RI* will be HIGH. If DI is HIGH, then DO/RI is HIGH and DO*/RI* is LOW. 5 GND Ground Connection 6 DO/RI Driver Output/Receiver Input, 485 Bus Pin. 7 DO*/RI* Driver Output/Receiver Input, 485 Bus Pin. 8V CC Positive Power Supply Connection: Recommended operating range for V CC is +4.75V to +5.25V. Unit Load A unit load for a RS-485 receiver is defined by the input current versus the input voltage curve. The gray shaded region is the defined operating range from −7V to +12V. The top border extending from −3V at 0 mA to +12V at +1 mA is defined as one unit load. Likewise, the bottom border ex- tending from +5V at 0 mA to −7V at −0.8 mA is also defined as one unit load (see Figure 18 ). A RS-485 driver is capable of driving up to 32 unit loads. This allows upto 32 nodes on a single bus. Although sufficient for many applications, it is sometime desirable to have even more nodes. For example an aircraft that has 32 rows with 4 seats per row could benefit from having 128 nodes on one bus. This would allow signals to be transferred to and from each individual seat to 1 main station. Usually there is one or two less seats in the last row of the aircraft near the restrooms and food storage area. This frees the node for the main station. The DS36C278, the DS36C279, and the DS36C280 all have 1 ⁄2 unit load and 1⁄4 unit load (UL) options available. These devices will allow upto 64 nodes or 128 nodes guaranteed over temperature depending upon which option is selected. The 1⁄2 UL option is available in industrial temperature and the 1⁄4 UL is available in commercial temperature. First, for a 1⁄2 UL device the top and bottom borders shown in Figure 18 are scaled. Both 0 mA reference points at +5V and −3V stay the same. The other reference points are +12V at +0.5 mA for the top border and −7V at −0.4 mA for the bottom border (see Figure 18 ). Second, for a 1⁄4 UL device the top and bottom borders shown in Figure 18 are scaled also. Again, both 0 mA reference points at +5V and −3V stay the same. The other reference points are +12V at +0.25 mA for the top border and −7V at −0.2 mA for the bottom border (see Figure 18 ). The advantage of the 1⁄2 UL and 1⁄4 UL devices is the increased number of nodes on one bus. In a single master multi-slave type of application were the number of slaves exceeds 32, the DS36C278/279/280 may save in the cost of extra devices like repeaters, extra media like cable, and/or extra components like resistors. The DS36C279 and DS36C280 have addition feature which offer more advantages. The DS36C279 has an automatic sleep mode function for power conscious applications. The DS36C280 has a slew rate control for EMI conscious appli- cations. Refer to the sleep mode and slew rate control portion of the application information section in the corre- sponding datasheet for more information on these features. 01205217 FIGURE 17. Typical Pin Connection www.national.com 7 |
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