(1) 功能塊FC實(shí)參的指針存到調(diào)用塊的L堆棧；
(2) 調(diào)用塊的地址和返回位置存儲(chǔ)在塊堆棧，調(diào)用塊的局部數(shù)據(jù)壓入L堆棧；
(3) 功能塊存儲(chǔ)臨時(shí)變量的L堆棧區(qū)被推入L堆棧上部；
(4) 當(dāng)被調(diào)用功能塊FC結(jié)束時(shí)，先前塊的信息存儲(chǔ)在塊堆棧中，臨時(shí)變量彈出L堆棧。
因?yàn)楣δ軌KFC不用背景數(shù)據(jù)塊，不能分配初始數(shù)值給功能塊FC的局部數(shù)據(jù)，所以必須給功能塊FC提供實(shí)參。
STEP 7為功能塊FC提供了一個(gè)特殊的返回值輸出參數(shù)(關(guān)鍵字：RET_VAL)。當(dāng)在文本文件中創(chuàng)建功能塊FC時(shí)，你可以在定義功能塊FC命令后輸入數(shù)據(jù)類(lèi)型(如BOOL或INT)。對(duì)文本文件進(jìn)行編譯時(shí)，STEP 7會(huì)自動(dòng)生成RET_VAL輸出參數(shù)。當(dāng)用STEP 7的程序編輯器(Program Editor)以增量模式創(chuàng)建功能塊FC時(shí)，可在FC的變量聲明表中聲明一個(gè)輸出參數(shù)RET_VAL，并指明其數(shù)據(jù)類(lèi)型。
功能塊編程與調(diào)用舉例
對(duì)功能塊編程分兩步進(jìn)行：步是定義局部變量(填寫(xiě)局部變量表)；第二步是編寫(xiě)要執(zhí)行的程序，可以用梯形圖或語(yǔ)句表兩種形式編程，并在編程過(guò)程中使用定義了的局部變量(數(shù)據(jù))。
定義局部變量的工作內(nèi)容包括：
(1) 分別定義形參、靜態(tài)變量和臨時(shí)變量(FC塊中不包括靜態(tài)變量)；
(2) 確定各變量的聲明類(lèi)型(Decl.)、變量名(Name)和數(shù)據(jù)類(lèi)型(Data Type)，還要為變量設(shè)置初始值(Initial Value)(盡管對(duì)有些變量初始值不一定有意義)。如果需要還可為變量注釋(Comment)。在增量編程模式下，STEP 7將自動(dòng)產(chǎn)生局部變量地址(Address)。
寫(xiě)功能塊程序時(shí)，可以用以下兩種方式使用局部變量：
(1) 使用變量名，此時(shí)變量名前加前綴“#”，以區(qū)別于在符號(hào)表中定義的符號(hào)地址。增量方式下，前綴會(huì)自動(dòng)產(chǎn)生。
(2) 直接使用局部變量的地址，這種方式只對(duì)背景數(shù)據(jù)塊和L堆棧有效。
在調(diào)用FB塊時(shí)，要說(shuō)明其背景數(shù)據(jù)塊。背景數(shù)據(jù)塊應(yīng)在調(diào)用前生成，其順序格式與變量聲明表必須保持一致。在增量方式下，調(diào)用FB塊時(shí)，STEP 7會(huì)自動(dòng)提醒并生成背景數(shù)據(jù)塊。此時(shí)也為背景數(shù)據(jù)塊設(shè)置了初始值，該初始值與變量聲明表中的相同。當(dāng)然也可以為背景數(shù)據(jù)塊設(shè)置當(dāng)前值(Current Value)，即存儲(chǔ)在CPU中的數(shù)值。
1．二分頻器
假設(shè)功能塊FC10是二分頻器產(chǎn)生程序，功能是對(duì)不同的輸入位進(jìn)行二分頻處理。以下給出了FC10的變量聲明表和語(yǔ)句表程序。在程序中使用了跳變沿檢測(cè)指令。
1) FC10的變量聲明表(見(jiàn)表5.3)

IDEC APW199DY USPP APW199DY
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IDEC APW299D-S-24V NSPP APW299DS24V
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VT50XX #31783

72V AMETEK LOW WIND GENERATOR MOTOR
Ametek USG Pressure Gauge 132784 P1929
Ametek Accuforce AF5-R-ND Gage with Load Cell, Scale, Lab, Tool, Test Equipment
Ametek Hunter Spring 50 lbs. Mechanical Force Gauge
Ametek Dixson BB101P Programmable Bargraph 0 Horiz
Ametek Brushless 24 VDC Vacuum motor and Driver
Ametek Accu Force Torque Chek Digital Torge Gauge 0-200 Oz In
2 NEW AMETEK 1025-D1SP 1025D1SP FOOT AND PALM SWITCH
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Ametek Gemco Patriot 950A1-6-F-X-X-?X-10-X Quik Stik LDT
Ametek Gemco Patriot 951A-C1-0100-N?2-X-E Quik Stik LDT
Ametek Prestolite 350 Amp Relay NSN 5945-01-165-10?65
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Dixson Instruments Bargraph BB101 AJTX4 / 20MADCV8850 Ametek NEW
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Pittman/Ametek Motor, 19.7:1 Ration GM9413C555
AMETEK 1025A1DPX DOUBLE POLE FOOT SWITCH
NOS! AMETEK SPRING RESILIENCY TESTER A799571 6635-00-470-15?47
NEW AMETEK WATER FILTRATION RB25-20 SEDIMENT CARTRIDGE 25 MICRON NOMINAL
Lamb Ametek 117572-12 Vacuum Blower
~ Lamb Ametek 116757-13 2-stage 5.7" Vacuum Motor M-W
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Ametek Lamb 115v 50/60hz Vacuum Motor 115962
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Ametek Lamb Electric Vacum motor
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VT50XX #31783

NICE LOT OF 15 ACCURAY Control Interface Boards (2175)
ACCURAY 2-067441-002 SCANNER PRINTED CIRCUIT BOARD MODULE CARD PCB 55216
ACCURAY 064851-001 FRAME POWER INTERFACE MODULE CARD 54739
ACCURAY SCANNER CIRCUIT BOARD BD40DM 60155750-001 PCB MODULE CARD HEDP-G 58689
ACCURAY 8-061594-003 PC BOARD AD-7-061595-00?3
ACCURAY 8-061588-002 I/O BOARD 8061588002
ACCURAY 9-085158-001 SCANNER CONTROL PCB PRINTED CIRCUIT BOARD CARD MODULE 58639
ABB ACCURAY 084903-001 TEST PANEL 084903001
ACCURAY 2-067441-002 PCB BOARD EXCELLENT CONDITION
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ACCURAY 1180M AD-6-054449-05?7 CONTROL PANEL DISPLAY MODULE ASSEMBLY 58700
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VT50XX #31783