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ICL3245IV-T Datasheet(PDF) 10 Page - Intersil Corporation |
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ICL3245IV-T Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 18 page 10 FN4878.8 February 27, 2006 Figure 7 illustrates the enhanced powerdown control logic. Note that once the ICL32XX enters powerdown (manually or automatically), the 30 second timer remains timed out (set), keeping the ICL32XX powered down until FORCEON transitions high, or until a transition occurs on a receiver or transmitter input. The INVALID output signal switches low to indicate that invalid levels have persisted on all of the receiver inputs for more than 30 µs (see Figure 8), but this has no direct effect on the state of the ICL32XX (see the next sections for methods of utilizing INVALID to power down the device). INVALID switches high 1 µs after detecting a valid RS-232 level on a receiver input. INVALID operates in all modes (forced or automatic powerdown, or forced on), so it is also useful for systems employing manual powerdown circuitry. The time to recover from automatic powerdown mode is typically 100 µs. Emulating Standard Automatic Powerdown If enhanced automatic powerdown isn’t desired, the user can implement the standard automatic powerdown feature (mimics the function on the ICL3221/ICL3223/ICL3243) by connecting the INVALID output to the FORCEON and FORCEOFF inputs, as shown in Figure 9. After 30 µs of invalid receiver levels, INVALID switches low and drives the ICL32XX into a forced powerdown condition. INVALID switches high as soon as a receiver input senses a valid RS- 232 level, forcing the ICL32XX to power on. See the “INVALID DRIVING FORCEON AND FORCEOFF” section of Table 2 for an operational summary. This operational mode is perfect for handheld devices that communicate with another computer via a detachable cable. Detaching the cable allows the internal receiver pull-down resistors to pull the inputs to GND (an invalid RS-232 level), causing the 30 µs timer to time-out and drive the IC into powerdown. Reconnecting the cablerestores valid levels, causing the IC to power back up. Hybrid Automatic Powerdown Options For devices which communicate only through a detachable cable, connecting INVALID to FORCEOFF (with FORCEON = 0) may be a desirable configuration. While the cable is attached INVALID and FORCEOFF remain high, so the enhanced automatic powerdown logic powers down the RS- 232 device whenever there is 30 seconds of inactivity on the RECEIVER INPUTS TRANSMITTER OUTPUTS INVALID OUTPUT V+ VCC 0 V- tINVL tINVH FIGURE 8. ENHANCED AUTOMATIC POWERDOWN, INVALID AND READY TIMING DIAGRAMS READY OUTPUT TRANSMITTER INPUTS tWU tAUTOPWDN tAUTOPWDN tWU INVALID REGION } FIGURE 9. CONNECTIONS FOR AUTOMATIC POWERDOWN WHEN NO VALID RECEIVER SIGNALS ARE PRESENT CPU I/O ICL32XX UART ICL3225, ICL3245 |
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