MAX244EQH-D中文资料(16)

+5V-Powered, Multichannel RS-232Drivers/ReceiversMAX220–MAX249

Tables 1a–1d define the control states. The MAX244has no control pins and is not included in these tables. The MAX246 has ten receivers and eight drivers withtwo control pins, each controlling one side of thedevice. A logic high at the A-side control input (ENA)causes the four A-side receivers and drivers to go intoa three-state mode. Similarly, the B-side control input(ENB) causes the four B-side drivers and receivers togo into a three-state mode. As in the MAX245, one A-side and one B-side receiver (RA5 and RB5) remainactive at all times. The entire device is put into shut-down mode when both the A and B sides are disabled(ENA= ENB= +5V).

The MAX247 provides nine receivers and eight driverswith four control pins. The ENRAand ENRBreceiverenable inputs each control four receiver outputs. TheENTAand ENTBtransmitter enable inputs each controlfour drivers. The ninth receiver (RB5) is always active.The device enters shutdown mode with a logic high onboth ENTAand ENTB.

The MAX248 provides eight receivers and eight driverswith four control pins. The ENRAand ENRBreceiverenable inputs each control four receiver outputs. TheENTAand ENTBtransmitter enable inputs control fourdrivers each. This part does not have an always-activereceiver. The device enters shutdown mode and trans-mitters go into a three-state mode with a logic high onboth ENTAand ENTB.

The MAX249 provides ten receivers and six drivers withfour control pins. The ENRAand ENRBreceiver enableinputs each control five receiver outputs. The ENTAand ENTBtransmitter enable inputs control three dri-vers each. There is no always-active receiver. Thedevice enters shutdown mode and transmitters go intoa three-state mode with a logic high on both ENTAandENTB. In shutdown mode, active receivers operate in alow-power receive mode at data rates up to 20kb/s.

__________Applications Information

Figures 5 through 25 show pin configurations and typi-cal operating circuits. In applications that are sensitiveto power-supply noise, VCCshould be decoupled toground with a capacitor of the same value as C1 andC2 connected as close as possible to the device.

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