【正文】 stem can still receive a signal that will activate it on mand and prepare it for munication at faster data rates. This operation conserves system power.Receiver and Transmitter EnableThe MAX225 and MAX245–MAX249 feature transmitter and receiver enable controls.The receivers have three modes of operation: fullspeed receive (normal active)? threestate (disabled)? and low power receive (enabled receivers continue to functionat lower data rates). The receiver enable inputs control the fullspeed receive and threestate modes. The transmitters have two modes of operation: fullspeed transmit (normal active) and threestate (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 lowpower receive mode when in shutdown.Shutdown—MAX222–MAX242On 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 for a hightolow 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 transmitterenable 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 current drops to less than 25μA and the receivers continue to operate in a lowpower receive mode. Driver outputs enter a highimpedance state (threestate mode). On the MAX225?all five receivers are controlled by the ENR input. On the MAX245? eight of the receiver outputs are controlled by the ENR input? while the remaining two receivers (RA5 and RB5) are always active. RA1–RA4 and RB1–RB4 are put in a threestate mode when ENR is a logic high.Th