正常情况下，需要先定义DB,才能引用；但是如果程序中找不到这个DB呢？

如果程序可以正常运行，那么结论只有一个，DB是程序运行后被创建的；尤其是对于300,400PLC ，这种情况比较常见，作为

SFB/C ,而在1200/1500 中，他们作为扩展指令使用；

所以即使你在程序中引用了一个未定义的地址也不会报错的一个原因就是，可能系统在等待你会在程序的运行阶段创建这个地址；

下面是帮助系统中的关于这些特殊系统块的列表，所以说西家从老早的S5/7 为了节约空间的而存在的指令，到了后面还会一直延续支持，确实还挺有趣；

Symbolic and numerical names of instructions    

Description

The instructions from the task card are comprised of functions (FC), function blocks (FB), system functions (SFC) and system function blocks (SFB) that are identified internally by numbers.

The following tables show the assignment of numerical and symbolic names.

Function blocks (FBs)

Numerical name

Symbolic name

FB 2

S_RCV

FB 3

S_SEND

FB 4

S_VSTAT

FB 5

S_VSET

FB 6

S_XON

FB 7

S_RTS

FB 8

S_V24

FB 8 (1)

USEND_S

FB 9 (1)

URCV_S

FB 14 (1)

GET_S

FB 15 (1)

PUT_S

FB 40 (1)

FTP_CMD

FB 46

PG_DIAL

FB 47

AS_DIAL

FB 48

SMS_SEND

FB 49

AS_MAIL

FB 52 (1)

PNIO_RW_REC

FB 53

PE_DS3_Write_ET200S

FB 54 (1)

PNIO_ALARM

FB 55

IP_CONFIG

FB 56 (1)

LOGICAL_TRIGGER

FB 60

SET_SW

FB 61

SET_SW_S

FB 62

TIMESTMP

FB 80

LEAD_LAG

FB 81

DCAT

FB 81

S_MODB

FB 82

MCAT

FB 83

IMC

FB 84

SMC

FB 85

DRUM

FB 86

PACK

FB 210

FW_TCP

FB 220

FW_IOT

FB 450 (2)

RED_IN_MGP

FB 451 (2)

RED_OUT_MGP

FB 452 (2)

RED_DIAG_MGP

FB 453 (2)

RED_STATUS_MGP

FB 815

PE_Start_End_Pause

FB 816

PE_CMD

FB 817 (1)

PE_I_DEV

(1) for S7-300

(2) for S7-400

(3) not for WinAC

(4) for S7-400, not for WinAC

(5) for WinAC

Functions (FCs)

Numerical name

Symbolic name

FC 0 (1)

PE_Error_RSP

FC 1 (1)

PE_Start_RSP

FC 1 (1)

DP_SEND

FC 2

CONCAT

FC 2 (1)

PE_End_RSP

FC 2 (1)

DP_RECV

FC 3 (1)

PE_List_Modes_RSP

FC 3 (1)

DP_DIAG

FC 4

DELETE

FC 4 (1)

PE_Get_Mode_RSP

FC 4 (1)

DP_CTRL

FC 5 (1)

PE_PEM_Status_RSP

FC 5 (1)

AG_SEND

FC 6 (1)

PE_Identify_RSP

FC 6 (1)

AG_RECV

FC 7

Asi_3422

FC 7 (1)

PE_Measurement_List_RSP

FC 7 (1)

AG_LOCK

FC 8 (1)

PE_Measurement_Value_RSP

FC 8 (1)

AG_UNLOCK

FC 10 (1)

AG_CNTRL

FC 11

FIND

FC 11 (1)

PNIO_SEND

FC 12 (1)

PNIO_RECV

FC 17

INSERT

FC 17

S_USST

FC 18

S_USSR

FC 19

S_USSI

FC 20

LEFT

FC 21

LEN

FC 22

LIMIT

FC 25

MAX

FC 26

MID

FC 27

MIN

FC 31

REPLACE

FC 32

RIGHT

FC 36

ENCO

FC 36

SEL

FC 37

DECO

FC 60

LOC_TIME

FC 61

BT_LT

FC 62

LT_BT

FC 62 (1)

C_CNTRL

FC 63

S_LTINT

FC 74 (3)

I_ABORT

FC 80

TONR

FC 82

RSET

FC 83

SET

FC 84

ATT

FC 85

FIFO

FC 86

TBL_FIND

FC 87

LIFO

FC 88

TBL

FC 89

TBL_WRD

FC 90

WSR

FC 91

WRD_TBL

FC 92

SHRB

FC 93

SEG

FC 98

BCDPL

FC 99

BITSUM

FC 100

RSETI

FC 101

SETI

FC 102

DEV

FC 103

CDT

FC 104

TBL_TBL

FC 105

SCALE

FC 106

UNSCALE

FC 450 (2)

RED_INIT_MGP

FC 451 (2)

RED_DEPA_MGP

(1) for S7-300

(2) for S7-400

(3) not for WinAC

(4) for S7-400, not for WinAC

(5) for WinAC

System function blocks (SFBs)

Numerical name

Symbolic name

SFB 0

CTU

SFB 1

CTD

SFB 2

CTUD

SFB 3

TP

SFB 4

TON

SFB 5

TOF

SFB 16 (4)

PRINT

SFB 19 (2)

START

SFB 20 (2)

STOP

SFB 21 (4)

RESUME

SFB 22 (2)

STATUS

SFB 23 (2)

USTATUS

SFB 29 (1)

HS_COUNT_300C

SFB 30 (1)

FREQ_MES_300C

SFB 31 (2)

NOTIFY_8P

SFB 32

DRUM_X

SFB 33 (2)

ALARM

SFB 34 (2)

ALARM_8

SFB 35 (2)

ALARM_8P

SFB 36 (2)

NOTIFY_8P

SFB 37 (2)

AR_SEND

SFB 38 (1)

HSC_A_B_300C

SFB 39 (1)

POS_300C

SFB 44 (1)

ANALOG_300C

SFB 46 (1)

DIGITAL_300C

SFB 47 (1)

COUNT_300C

SFB 48 (1)

FREQUENC_300C

SFB 49 (1)

PULSE_300C

SFB 52

RDREC

SFB 53

WRREC

SFB 54

RALRM

SFB 60 (1)

SEND_PTP_300C

SFB 61 (1)

RCV_PTP_300C

SFB 62 (1)

RES_RCVB_300C

SFB 63 (1)

SEND_RK_300C

SFB 64 (1)

FETCH_RK_300C

SFB 65 (1)

SERVE_RK_300C

SFB 73

RCVREC

SFB 74

PRVREC

SFB 75

SALRM

SFB 81

RD_DPAR

SFB 104

IP_CONF

SFB 65001 (5)

CREA_COM

SFB 65002 (5)

EXEC_COM

SFB 65002 (5)

ASYN_COM

(1) for S7-300

(2) for S7-400

(3) not for WinAC

(4) for S7-400, not for WinAC

(5) for WinAC

System functions (SFCs)

Numerical name

Symbolic name

SFC 2

SET_RTM

SFC 3

CTRL_RTM

SFC 4

READ_RTM

SFC 5

GADR_LGC

SFC 7 (3)

DP_PRAL

SFC 9 (2)

EN_MSG

SFC 10 (2)

DIS_MSG

SFC 11

DPSYC_FR

SFC 12

D_ACT_DP

SFC 13

DPNRM_DG

SFC 14

DPRD_DAT

SFC 17

ALARM_SQ

SFC 18

ALARM_S

SFC 19

ALARM_SC

SFC 20

BLKMOV

SFC 21

FILL

SFC 22

CREAT_DB

SFC 23

DEL_DB

SFC 24

TEST_DB

SFC 26 (2)

UPDAT_PI

SFC 27 (2)

UPDAT_PO

SFC 28

SET_TINT

SFC 29

CAN_TINT

SFC 30

ACT_TINT

SFC 31

QRY_TINT

SFC 32

SRT_DINT

SFC 33

CAN_DINT

SFC 34

QRY_DINT

SFC 35 (4)

MP_ALM

SFC 36

MSK_FLT

SFC 37

DMSK_FLT

SFC 38

READ_ERR

SFC 39

DIS_IRT

SFC 40

EN_IRT

SFC 41

DIS_AIRT

SFC 42

EN_AIRT

SFC 43

RE_TRIGR

SFC 44

REPL_VAL

SFC 46

STP

SFC 47

WAIT

SFC 48 (4)

SNC_RTCB

SFC 49

LGC_GADR

SFC 50

RD_LGADR

SFC 51

RDSYSST

SFC 52

WR_USMSG

SFC 54 (2)

RD_DPARM

SFC 55

WR_PARM

SFC 56

WR_DPARM

SFC 57

PARM_MOD

SFC 58

WR_REC

SFC 59

RD_REC

SFC 60 (4)

GD_SND

SFC 61 (4)

GD_RCV

SFC 62 (2)

CONTROL

SFC 64

TIME_TCK

SFC 64

RD_SINFO

SFC 65 (3)

X_SEND

SFC 66 (3)

X_RCV

SFC 67 (3)

X_GET

SFC 68 (3)

X_PUT

SFC 69 (3)

X_ABORT

SFC 70

GEO_LOG

SFC 71

LOG_GEO

SFC 72 (3)

I_GET

SFC 73 (3)

I_PUT

SFC 75

SET_ADDR

SFC 78 (2)

OB_RT

SFC 79

SETP

SFC 80

RESETP

SFC 81

UBLKMOV

SFC 82 (1) (6)

CREA_DBL

SFC 83 (1) (6)

READ_DBL

SFC 84 (1) (6)

WRIT_DBL

SFC 85 (6)

CREA_DB

SFC 87 (2)

C_DIAG

SFC 90 (4)

H_CTRL

SFC 99

WWW

SFC 100 (2)

SET_CLKS

SFC 101

RTM

SFC 102 (1)

RD_DPARA

SFC 103 (3)

DP_TOPOL

SFC 104 (2)

CIR

SFC 105

READ_SI

SFC 106

DEL_SI

SFC 107

ALARM_DQ

SFC 108

ALARM_D

SFC 109

PROTECT

SFC 112

PN_IN

SFC 113

PN_OUT

SFC 114

PN_DP

SFC 126

SYNC_PI

SFC 127

SYNC_PO

SFC 154

DPWR_DAT

(1) for S7-300

(2) for S7-400

(3) not for WinAC

(4) for S7-400, not for WinAC

(5) for WinAC