Choosing the Right RS-232 Tran

文章摘要：Maxim also offers a series of RS-232 transceivers that operate from voltages as low as 2.35V. Maxim even has two ultra low power supply RS-232 transceiver, the MAX218 and MAX3218, which use an inductor along with capacitors to allow operation with a single +1.8V supply. Increased Battery Life throug

Choosing the Right RS-232 Tran,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com

Maxim also offers a series of RS-232 transceivers that operate from voltages as low as 2.35V. Maxim even has two ultra low power supply RS-232 transceiver, the MAX218 and MAX3218, which use an inductor along with capacitors to allow operation with a single +1.8V supply.

Increased Battery Life through Autoshutdown Techniques

Many RS-232 transceivers provide a simple shutdown feature that is activated by applying a logic level to the shutdown pin. Since most RS-232 devices are only used for a short period of time, the shutdown feature can save energy and increase the run-time of portable equipment batteries.

Other RS-232 devices incorporate a more advanced feature called Autoshutdown, which typically limits the shutdown supply current to 1uA. These devices can determine whether a transmission cable is attached to the RS-232 transceiver. If a cable is not attached to the RS-232 transceiver, the unit will go into shutdown until the presence of a transmission cable is detected. A transceiver equipped with the Autoshutdown feature monitors the RS-232 signals at its receiver inputs to determine whether a cable is connected. When a cable is not present, the signals at the RS-232 receiver inputs are approximately 0V. If the transceiver detects that all the receiver inputs are between -0.3V and +0.3V for greater than 30µS, it assumes that a valid transmitter cable is not connected and will automatically put itself into a low-power mode (shutdown). The part will automatically take itself out of shutdown if any one of the receiver's inputs exceeds +2.7V (i.e., whenever the cable is reconnected). This feature can be overridden with signals that force the device on or off. See Figure 1. The MAX3228E, MAX3229E and the MAX3246E are three examples of transceivers that incorporate the Autoshutdown feature.


Figure 1. The Autoshutdown Plus logic incorporated in an RS-232 transceiver, allows the transceiver to stay powered on as long it detects signal transactions at its transmitter or receiver inputs within 30-second intervals. Otherwise the transceiver is automatically powered down when the interval between signals is greater than 30 seconds. Logic levels applied to the FORCEON and active-low FORCEOFF inputs turn the device's power on and off overriding the Autoshutdown Plus logic controlled by receiver and transmitter input signal activity.

Autoshutdown Plus is similar to Autoshutdown in that it is designed to save power by shutting down the RS-232 device whenever it is not in use. The Autoshutdown Plus shuts down the transceiver when the cables are disconnected, and when the cable is connected and data edges haven't been detected for 30 seconds or more. This way you can get the benefit of an automated shutdown regardless of whether the cable is connected. Autoshutdown-Plus devices monitor both the RS-232 receiver inputs and the digital transmitter inputs for signal activity; shutdown ensues if no activity is present on any of these lines for 30 seconds. As with Autoshutdown, you can force on or off the device using pins that override the Autoshutdown Plus feature. See Figure 1. The MAX3238E, MAX3380E, MAX3381E, MAX3226E and the MAX3246E are five examples of transceivers that incorporate the Autoshutdown Plus feature.

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