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RCV
先进先出
串行 至
并行的
流动
控制
XMT
先进先出
并行的
至 串行
流动
控制
并行的
至 串行
流动
控制
串行 至
并行的
流动
控制
XMT
先进先出
RCV
先进先出
ACE1 ACE2
D7−D0
SIN SOUT
RTS CTS
SOUT SIN
CTS RTS
D7−D0
自动-rts(seefigure2)
自动-cts(seefigure2)
enablingautoflowcontrolandauto-cts
自动-ctsandauto-rtsfunctionaltiming
开始 位 0 −7 开始 位 0 −7 开始 位 0 −7
停止 停止 停止
SOUT
CTS
TL16C2550
SLWS161–JUNE2005
figure2.autoflowcontrol(自动-rtsandauto-cts)例子
自动-rtsdataflowcontroloriginatesinthereceivertimingandcontrolblock(seefunctionalblockdiagram)和
islinkedtotheprogrammedreceiverfifotriggerlevel.whenthereceiverfifolevelreachesatriggerlevelof
1,4,or8(seefigure3),rtsisdeasserted.withtriggerlevelsof1,4,and8,thesendingacemaysendan
additionalbyteafterthetriggerlevelisreached(assumingthesendingacehasanotherbytetosend)becauseit
maynotrecognizethedeassertionofrtsuntilafterithasbegunsendingtheadditionalbyte.rtsis
automaticallyreassertedoncethercvfifoisemptiedbyreadingthereceiverbufferregister.
whenthetriggerlevelis14(seefigure4),rtsisdeassertedafterthefirstdatabitofthe16thcharacteris
presentontherxline.rtsisreassertedwhenthercvfifohasatleastoneavailablebytespace.
thetransmittercircuitrychecksctsbeforesendingthenextdatabyte.whenctsisactive,itsendsthenext
字节.tostopthetransmitterfromsendingthefollowingbyte,ctsmustbereleasedbeforethemiddleofthelast
stopbitthatiscurrentlybeingsent(seefigure2).theauto-ctsfunctionreducesinterruptstothehostsystem.
whenflowcontrolisenabled,ctslevelchangesdonottriggerhostinterruptsbecausethedeviceautomatically
controlsitsowntransmitter.withoutauto-cts,thetransmittersendsanydatapresentinthetransmitfifoanda
receiveroverrunerrormayresult.
autoflowcontrolisenabledbysettingmodemcontrolregisterbits5(autoflowenableorafe)and1(rts)toa1.
autoflowincorporatesbothauto-rtsandauto-cts.whenonlyauto-ctsisdesired,bit1inthemodemcontrol
registershouldbecleared(thisassumesthatacontrolsignalisdrivingcts).
figure3.ctsfunctionaltimingwaveforms
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