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MAX232-ACWE Datasheet(PDF) 15 Page - Maxim Integrated Products |
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MAX232-ACWE Datasheet(HTML) 15 Page - Maxim Integrated Products |
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15 / 38 page  +5V-Powered, Multichannel RS-232 Drivers/Receivers nominal 5k Ω values. The receivers implement Type 1 interpretation of the fault conditions of V.28 and EIA/TIA-232E. The receiver input hysteresis is typically 0.5V with a guaranteed minimum of 0.2V. This produces clear out- put transitions with slow-moving input signals, even with moderate amounts of noise and ringing. The receiver propagation delay is typically 600ns and is independent of input swing direction. Low-Power Receive Mode The low-power receive mode feature of the MAX223, MAX242, and MAX245–MAX249 puts the IC into shut- down mode but still allows it to receive information. This is important for applications where systems are periodi- cally awakened to look for activity. Using low-power receive mode, the system can still receive a signal that will activate it on command and prepare it for communi- cation at faster data rates. This operation conserves system power. Negative Threshold—MAX243 The MAX243 is pin compatible with the MAX232A, differ- ing only in that RS-232 cable fault protection is removed on one of the two receiver inputs. This means that control lines such as CTS and RTS can either be driven or left unconnected without interrupting communication. Different cables are not needed to interface with different pieces of equipment. The input threshold of the receiver without cable fault protection is -0.8V rather than +1.4V. Its output goes positive only if the input is connected to a control line that is actively driven negative. If not driven, it defaults to the 0 or “OK to send” state. Normally‚ the MAX243’s other receiver (+1.4V threshold) is used for the data line (TD or RD)‚ while the negative threshold receiver is con- nected to the control line (DTR‚ DTS‚ CTS‚ RTS, etc.). Other members of the RS-232 family implement the optional cable fault protection as specified by EIA/TIA- 232E specifications. This means a receiver output goes high whenever its input is driven negative‚ left uncon- nected‚ or shorted to ground. The high output tells the serial communications IC to stop sending data. To avoid this‚ the control lines must either be driven or connected with jumpers to an appropriate positive volt- age level. Shutdown—MAX222–MAX242 On the MAX222‚ MAX235‚ MAX236‚ MAX240‚ and MAX241‚ all receivers are disabled during shutdown. On the MAX223 and MAX242‚ two receivers continue to operate in a reduced power mode when the chip is in shutdown. Under these conditions‚ the propagation delay increases to about 2.5µs for a high-to-low input transition. When in shutdown, the receiver acts as a CMOS inverter with no hysteresis. The MAX223 and MAX242 also have a receiver output enable input (EN for the MAX242 and EN for the MAX223) that allows receiver output control independent of SHDN (SHDN for MAX241). With all other devices‚ SHDN (SHDN for MAX241) also disables the receiver outputs. The MAX225 provides five transmitters and five receivers‚ while the MAX245 provides ten receivers and eight transmitters. Both devices have separate receiver and transmitter-enable controls. The charge pumps turn off and the devices shut down when a logic high is applied to the ENT input. In this state, the supply cur- rent drops to less than 25µA and the receivers continue to operate in a low-power receive mode. Driver outputs enter a high-impedance state (three-state mode). On the MAX225‚ all five receivers are controlled by the ENR input. On the MAX245‚ eight of the receiver out- puts are controlled by the ENR input‚ while the remain- ing two receivers (RA5 and RB5) are always active. RA1–RA4 and RB1–RB4 are put in a three-state mode when ENR is a logic high. Receiver and Transmitter Enable Control Inputs The MAX225 and MAX245–MAX249 feature transmitter and receiver enable controls. The receivers have three modes of operation: full-speed receive (normal active)‚ three-state (disabled)‚ and low- power receive (enabled receivers continue to function at lower data rates). The receiver enable inputs control the full-speed receive and three-state modes. The transmitters have two modes of operation: full-speed transmit (normal active) and three-state (disabled). The transmitter enable inputs also control the shutdown mode. The device enters shutdown mode when all transmitters are disabled. Enabled receivers function in the low-power receive mode when in shutdown. Maxim Integrated 15 MAX220–MAX249 MAX220–MAX249 |
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Similar Description - MAX232-ACWE |
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