代理(li)焦作西門子PLC模塊 一級代理(li)商

該智(zhi)能轉換器(qi)必須解(jie)決兩個關鍵問題(ti)即如何從RS-232線上獲(huo)得電路和RS-485/RS-422接口驅(qu)動所需的功率和如何智(zhi)能控制RS-485/RS-422的收發使能
3.1.電源方案
標準的(de)(de)RS-232 定(ding)義中有三個發送(song)信號TXD RTS 和DTR 每(mei)根線上(shang)的(de)(de)典(dian)型輸出(chu)電(dian)流為(wei)(wei)8mA/ 12V 考慮到(dao)TXD為(wei)(wei)負(fu)電(dian)平(ping)處于停止發送(song)或發送(song)數字1 時(shi)的(de)(de)時(shi)間較多因而(er)電(dian)源轉(zhuan)換決定(ding)采用負(fu)電(dian)源輸入(ru)(ru)以最大(da)限(xian)度地(di)增加(jia)電(dian)源輸入(ru)(ru)功率(lv)(lv)(lv)升壓至所需的(de)(de)工作(zuo)電(dian)源從RTS和DTR上(shang)輸入(ru)(ru)功率(lv)(lv)(lv)=2*8*12mW=192mW,另外由于通訊為(wei)(wei)間歇工作(zuo)方式(shi)所以輸入(ru)(ru)電(dian)源端的(de)(de)儲能電(dian)容和TXD 為(wei)(wei)負(fu)電(dian)平(ping)時(shi)能夠補充一(yi)定(ding)的(de)(de)功率(lv)(lv)(lv)假(jia)設(she)我們(men)設(she)計(ji)一(yi)個效率(lv)(lv)(lv)為(wei)(wei)85% 輸出(chu)電(dian)壓為(wei)(wei)3V 的(de)(de)DC-DC ;轉(zhuan)換器則輸出(chu)電(dian)流可(ke)達(da)54.4mA
3.2.智(zhi)能控制收發使能
RS-232通(tong)(tong)(tong)訊(xun)(xun)接(jie)口采用(yong)(yong)電平方(fang)式傳輸適(shi)用(yong)(yong)于(yu)點(dian)-點(dian)通(tong)(tong)(tong)訊(xun)(xun)無(wu)須(xu)專(zhuan)門的(de)收發(fa)(fa)使(shi)能(neng)控制而對于(yu)RS-485/RS-422通(tong)(tong)(tong)訊(xun)(xun)接(jie)口則不同由于(yu)采用(yong)(yong)差(cha)分電平方(fang)式傳輸且允(yun)許在(zai)一條通(tong)(tong)(tong)訊(xun)(xun)總線上掛接(jie)多個節點(dian)必然(ran)要(yao)求各個節點(dian)能(neng)夠獨立地控制總線驅動器關斷(duan)或(huo)打(da)(da)開(kai)保證不會影響到(dao)其它(ta)節點(dian)的(de)正常通(tong)(tong)(tong)訊(xun)(xun)為了(le)簡化與(yu)轉換(huan)器RS-232 接(jie)口端相連的(de)軟(ruan)(ruan)件(jian)(jian)工(gong)作(zuo)更(geng)重要(yao)的(de)是(shi)為了(le)提高(gao)本轉換(huan)器的(de)通(tong)(tong)(tong)用(yong)(yong)性和(he)靈活(huo)性即插即用(yong)(yong)無(wu)須(xu)要(yao)求用(yong)(yong)戶更(geng)改任何相關軟(ruan)(ruan)件(jian)(jian)和(he)硬件(jian)(jian)本轉換(huan)器內(nei)置微處(chu)理(li)器實現(xian)收發(fa)(fa)使(shi)能(neng)的(de)智(zhi)能(neng)控制具體方(fang)法微處(chu)理(li)器在(zai)檢(jian)測到(dao)UART 的(de)通(tong)(tong)(tong)信起始(shi)位后打(da)(da)開(kai)發(fa)(fa)送(song)使(shi)能(neng)允(yun)許串行數據發(fa)(fa)送(song)至RS-485/RS-422 通(tong)(tong)(tong)訊(xun)(xun)網絡微處(chu)理(li)器根(gen)據所設(she)定(ding)的(de)波特率(lv)延時(shi)至UART 停止位發(fa)(fa)送(song)一半時(shi)例(li)如(ru)11位格式時(shi)延時(shi)10.5T,T=1/fBAUD ,開(kai)始(shi)檢(jian)測是(shi)否有下一個起始(shi)位到(dao)來(lai)在(zai)時(shi)間T內(nei)若(ruo)有下一個起始(shi)位到(dao)來(lai)則保持發(fa)(fa)送(song)狀態否則將關閉發(fa)(fa)送(song)使(shi)能(neng)結束數據發(fa)(fa)送(song)
4. 硬件設計
由于(yu)本轉換(huan)器供(gong)電(dian)來(lai)自RS-232信號線其輸入功率受到限制因(yin)而在本設計中將盡可能(neng)地采用+3V供(gong)電(dian)的低功耗器件保(bao)證總電(dian)流小(xiao)于(yu)54.4mA 主要(yao)包括4個部分DC-DC轉換(huan)器RS-232接(jie)口RS-485/RS-422接(jie)口和微(wei)處理器分別介紹如下
4.1. DC-DC轉(zhuan)換器
顯(xian)然(ran)還沒有一個DC-DC 轉(zhuan)換器能夠(gou)(gou)直接實現(xian)-12V 輸(shu)入(ru)(ru)+3V 輸(shu)出(chu)(chu)的(de)(de)IC 但是如(ru)果我們利用(yong)現(xian)有的(de)(de)IC 稍作改動即(ji)可實現(xian)該(gai)功能圖2 所示的(de)(de)DC-DC 轉(zhuan)換電(dian)路(lu)就是利用(yong)MAX761 實現(xian)的(de)(de)-12V 輸(shu)入(ru)(ru)+3V 輸(shu)出(chu)(chu)效率(lv)高于(yu)(yu)85%的(de)(de)升(sheng)壓(ya)DC-DC 轉(zhuan)換器該(gai)轉(zhuan)換器實際輸(shu)入(ru)(ru)電(dian)壓(ya)范(fan)圍(wei)為(wei)-2.5V 至(zhi)-13.5V 靜(jing)態工作電(dian)流(liu)僅I1=120 A 具(ju)有輸(shu)出(chu)(chu)電(dian)流(liu)大于(yu)(yu)54.4mA的(de)(de)能力如(ru)果前端輸(shu)入(ru)(ru)功率(lv)未(wei)受到限制(zhi)則輸(shu)出(chu)(chu)電(dian)流(liu)可達300mA以上(shang)由(you)于(yu)(yu)MAX761采用(yong)高效率(lv)的(de)(de)PFM 控制(zhi)方式,而且在本電(dian)路(lu)中,開(kai)關損耗較小(xiao)(因為(wei)開(kai)關電(dian)流(liu)小(xiao)于(yu)(yu)負載電(dian)流(liu)),所以能夠(gou)(gou)達到比MAX761 典型應用(yong)更高的(de)(de)效率(lv)(MAX761 典型應用(yong)效率(lv)為(wei)86%) 輸(shu)出(chu)(chu)電(dian)壓(ya)由(you)下列方程(cheng)確定
VOUT=VREF*R1/R2+0.7(V) 其中VREF=1.5V

-12V至3V 效(xiao)率(lv)高(gao)于(yu)85%的DC-DC轉換器
4.2. RS-232接口
本轉(zhuan)換器只需要(yao)(yao)(yao)一片單(dan)發/單(dan)收RS-232接(jie)口就可(ke)以滿足要(yao)(yao)(yao)求(qiu)但(dan)必須要(yao)(yao)(yao)求(qiu)+3V單(dan)電(dian)(dian)源工作工作電(dian)(dian)流盡可(ke)能(neng)地小的接(jie)口電(dian)(dian)路MAX3221/MAX3221E 帶15kVESD保護(hu)剛(gang)好能(neng)夠滿足上述要(yao)(yao)(yao)求(qiu)具有1TX/1RX 其工作電(dian)(dian)壓+3V至+5.5V, 僅1 A的靜態電(dian)(dian)流負(fu)載電(dian)(dian)流小于I2=2mA
4.3. RS-485/RS-422接口
為(wei)(wei)兼顧RS-485/RS-422 接(jie)口中半雙工(gong)(gong)和全雙工(gong)(gong)的要求本轉換(huan)器(qi)采(cai)用MAX3491 作(zuo)(zuo)為(wei)(wei)RS-485/RS-422 接(jie)口電路(lu)其主要指標為(wei)(wei)+3V 至+3.6V 單電源工(gong)(gong)作(zuo)(zuo)工(gong)(gong)作(zuo)(zuo)電流1mA,驅動60負載時(shi)半雙工(gong)(gong)時(shi)兩個120 終端匹(pi)配電阻(zu)的并(bing)聯值峰值電流可達(da)I3=3V/60 =50mA半雙工(gong)(gong)和全雙工(gong)(gong)工(gong)(gong)作(zuo)(zuo)方式(shi)是通過(guo)跳(tiao)線器(qi)來(lai)設(she)置(zhi)的見圖3
4.4. 微處(chu)理器(qi)
在(zai)本轉換器(qi)中(zhong)微處理器(qi)所要完成(cheng)的(de)任務很簡單僅需(xu)要幾根(gen)I/O 線(xian)(xian)即(ji)可實現參(can)數(shu)的(de)設置和(he)(he)發送(song)使(shi)能的(de)自(zi)動控(kong)制(zhi)(zhi)實際選(xuan)擇中(zhong)采用(yong)(yong)(yong)Microchip公(gong)司的(de)PIC12C508A其(qi)主要指標為(wei)工(gong)作電(dian)流I4<1.0mA(工(gong)作電(dian)壓3V 頻率(lv)4MHz),6 條(tiao)I/O 線(xian)(xian)512kByte 的(de)ROM 其(qi)中(zhong)GP0 GP1 GP4和(he)(he)GP5四個引(yin)腳(jiao)設定對(dui)應(ying)于(yu)16 種(zhong)常用(yong)(yong)(yong)波(bo)特率(lv)300 600 1200至(zhi)38.4Kbps等8 種(zhong)以(yi)及(ji)900 1800 至(zhi)115.4Kbps等8種(zhong)的(de)延時(shi)時(shi)間GP3對(dui)應(ying)于(yu)10位或11位串(chuan)行數(shu)據(ju)格(ge)式GP2為(wei)TXD輸入用(yong)(yong)(yong)來檢測UART何時(shi)發送(song)和(he)(he)停止數(shu)據(ju)GP1為(wei)復用(yong)(yong)(yong)輸出(chu)引(yin)腳(jiao)用(yong)(yong)(yong)來控(kong)制(zhi)(zhi)MAX3491的(de)發送(song)使(shi)能控(kong)制(zhi)(zhi)端GP0也(ye)為(wei)復

本轉換器(qi)的(de)最大電流(liu)總和(he)<I1+I2+I3+I4=0.12+2.0+ 50.0+1.0=53.12mA 小于DC-DC轉換器(qi)的(de)最小輸出電流(liu)54.4mA 因(yin)而通過RS-232信號線為(wei)本電路(lu)(lu)供電是可行(xing)的(de)實際上由于輸入電源(yuan)(yuan)端的(de)儲能(neng)電容E1 和(he)TXD 為(wei)負(fu)電平時能(neng)夠為(wei)電路(lu)(lu)補充一定的(de)功率所以(yi)設計上留有(you)較大的(de)電源(yuan)(yuan)功率裕量
5. 軟(ruan)件設計
本轉換器的(de)軟件設(she)計較為簡單(dan)微處理(li)器復位(wei)后將所(suo)有(you)的(de)I/O 口設(she)為輸入(ru)并(bing)讀入(ru)所(suo)有(you)的(de)I/O 狀態(tai)(tai)保(bao)存到寄存器將GP2 和GP3 改設(she)為輸出狀態(tai)(tai)并(bing)輸出低電平使(shi)(shi)RS-485/RS-422 接(jie)口處于禁(jin)止發(fa)送(song)允許(xu)接(jie)收(shou)的(de)狀態(tai)(tai)CPU 根據(ju)GPIO 的(de)初始狀態(tai)(tai)確定出用戶設(she)定的(de)通(tong)訊(xun)(xun)波特率(lv)和串(chuan)行數(shu)據(ju)格式從而預置內部的(de)延(yan)(yan)時(shi)(shi)設(she)定CPU 檢測(ce)(ce)到UART開(kai)始通(tong)訊(xun)(xun)后打(da)開(kai)發(fa)送(song)使(shi)(shi)能(neng)經內部預置延(yan)(yan)時(shi)(shi)后開(kai)始在(zai)一(yi)個位(wei)寬時(shi)(shi)間內檢測(ce)(ce)是否有(you)下(xia)一(yi)個起始位(wei)到來如檢測(ce)(ce)到則重(zhong)新延(yan)(yan)時(shi)(shi)等(deng)待否則關(guan)閉(bi)(bi)發(fa)送(song)使(shi)(shi)能(neng)結束(shu)當前(qian)通(tong)訊(xun)(xun)重(zhong)新檢測(ce)(ce)UART的(de)起始位(wei)對于半雙工通(tong)訊(xun)(xun)方式允許(xu)發(fa)送(song)使(shi)(shi)能(neng)前(qian)應該(gai)關(guan)閉(bi)(bi)接(jie)收(shou)使(shi)(shi)能(neng)而在(zai)發(fa)送(song)使(shi)(shi)能(neng)關(guan)閉(bi)(bi)后才打(da)開(kai)接(jie)收(shou)使(shi)(shi)能(neng)對于全雙工通(tong)訊(xun)(xun)方式其接(jie)收(shou)使(shi)(shi)能(neng)可(ke)以不受此信號控(kong)制(zhi)而可(ke)以直接(jie)通(tong)過(guo)跳(tiao)線接(jie)地始終允許(xu)接(jie)收(shou)
6. 結論
在本RS-232到RS-485/RS-422接(jie)(jie)(jie)口的(de)智(zhi)能轉(zhuan)換器設計(ji)中(zhong)除了本身這個產品具有較高的(de)應(ying)用價值(zhi)外文(wen)中(zhong)所涉(she)及的(de)RS-232信號線供電(dian)(dian)方案由于(yu)其高效率大電(dian)(dian)流輸出能力在許多(duo)基(ji)于(yu)RS-232 接(jie)(jie)(jie)口的(de)應(ying)用中(zhong)都能夠(gou)很好地滿足應(ying)用另(ling)外這種智(zhi)能控制RS-485/RS-422 接(jie)(jie)(jie)口的(de)收(shou)發使能的(de)思想(xiang)在擴展基(ji)于(yu)RS-485/RS-422 接(jie)(jie)(jie)口的(de)網絡分支及延伸通訊距離都能夠(gou)得到很好的(de)應(ying)用

要(yao)單片機完(wan)成(cheng)(cheng)一(yi)項(xiang)基(ji)本任務(wu)，必須將任務(wu)分解成(cheng)(cheng)一(yi)些(xie)具體步驟，再要(yao)求(qiu)它(ta)去(qu)逐(zhu)(zhu)項(xiang)執行每個步驟，還要(yao)對它(ta)下命令(ling)(ling)。該命令(ling)(ling)在單片機術語中(zhong)稱(cheng)為“指(zhi)(zhi)令(ling)(ling)"(Inetruction)。完(wan)成(cheng)(cheng)一(yi)項(xiang)任務(wu)所(suo)需(xu)的(de)所(suo)有指(zhi)(zhi)令(ling)(ling)的(de)有序(xu)集(ji)合(he)就稱(cheng)為“程序(xu)"(Programm)。這些(xie)指(zhi)(zhi)令(ling)(ling)要(yao)預先(xian)一(yi)條一(yi)條順序(xu)地(di)放到(dao)單片機的(de)程序(xu)存貯器中(zhong)，單片機在運(yun)行時，片中(zhong)的(de)CPU從(cong)程序(xu)存貯器中(zhong)逐(zhu)(zhu)條有序(xu)取(qu)出指(zhi)(zhi)令(ling)(ling)，執行指(zhi)(zhi)令(ling)(ling)，并將有關指(zhi)(zhi)令(ling)(ling)執行完(wan)畢，即可(ke)完(wan)成(cheng)(cheng)既定任務(wu)。