西門子PLC寄存器AR1和AR2使用重要事項

1、1、 STEP7使用的AR1地址寄存器來訪問FC接口（包括in out 和inout）以及FB接口的復(fù)雜型參數(shù)，如array、struct date_and_time.這就是我們?yōu)槭裁丛贔C接口中使用out型參數(shù)訪問DB1.DBXX會出現(xiàn)錯誤，因為AR1寄存器不能完全描述DB1.DBXX地址，完全描述需要6長度字節(jié)。2、 FC FB 本質(zhì)上一樣調(diào)用FB相當于在FC里opn di ，并使用ar2來索引變量FB的優(yōu)點是數(shù)據(jù)塊里的變量可按名字使用，僅僅是顯示而已，執(zhí)行效率和fc一樣3、 fb中為了方便背景數(shù)據(jù)塊參數(shù)的尋址，自動使用ar2寄存器，ar2寄存器指向背景數(shù)據(jù)塊的首地址p#dbx0.0，如果

2、改變了這個寄存器的值，你再訪問背景數(shù)據(jù)塊參數(shù)時將不會得到正確的數(shù)值.所以，在fb里使用ar2寄存器要小心，對這兩個寄存器改變后不要再使用背景數(shù)據(jù)塊參數(shù)，當要使用背景數(shù)據(jù)塊參數(shù)時要先恢復(fù)這兩個寄存器的值。有一個常用的用法是多重背景fb的接口參數(shù)的尋址用法，需要用到ar2:(因為在多重背景中，變量的地址并不是其在背景數(shù)據(jù)塊中的絕對地址，而是其相對于ar2的偏移地址),所以：在多重背景fb中，如果要得到某變量variable在背景數(shù)據(jù)塊中的絕對地址，可以使用以下代碼：tar2/將地址寄存器裝入累加器ac1(偏移量)，也就是多重背景fb中第一個變量在背景數(shù)據(jù)塊中的地址。addw#16#00ffffff

3、/關(guān)閉區(qū)域idlp#variable/裝載變量的地址+d/加上偏移量和變量地址lar1/將結(jié)果保存到地址寄存器ar1中Notes on Changing the Contents of RegistersIf you use the programming options below together with the registers and accumulators listed, you must make sure you restore the contents of the registers or accumulators yourself, otherwise errors

4、may occur. Using the following higher-language constructions may cause the contents of the DB register and address register AR1 to be modified:Fully-qualified DB access (for example, DB20.DBW10) as an actual parameter for a function (FC) Function block (FB) and multiple-instance callsStructure compo

5、nents of a formal parameter as an address within an FC or FBStructure components of a formal parameter as an actual parameter for an FC or FBWith FB, FC, and multiple-instance calls, you should not use the RLO or accumulator 1 or 2 as additional (implicit) parameters.The DI register and address regi

6、ster AR2 are used on the system side for the FB and multiple-instance calls and should not therefore be modified within FBs.Address register AR1 is used by some of the loadable standard blocks. The command L P#parameter_name loads the address offset of the specified parameter within an FB, relative to address register AR2. In order to determine the absolute offset in the instance data block in multiple-instance type FBs, you must also add the area-internal poin