The s7read node

Read data from a siemens s7 plc via the snap7 library using the iso on tcp protocol. The node is tested to read data from S7 300 and S7 1500 CPUs, but should be able to read data from any S7 PLC that supports the S7 comm protocol.

Reading can be done periodically and/or triggered via incoming data-items. If the every parameter is not given, reading will be done only with trigger data-items.

• Data addressing can be done in a Step7 schema or with a slightly different schema used in node-red (although the step7 variant is preferred). See table below for more information about addressing.

Optimzation when reading data

• The node will optimize reading by treating contiguous values as one reading var. Thus more data can be read in one go.

• since 0.20.0: when optimized is set to true (default), then optimization and reading will be done outside of the node. All variables from all s7read nodes, that target the same PLC are optimized as a whole, this makes it possible to take advantage of the maximum PDU size. This will possibly lead to more than one request for a specific time slot, if there are many vars to read. In optimized mode, it does not make a difference, if we use many s7read nodes, where every node just reads a view vars, or if we have only one s7read node, that reads a lot of vars (or anything in between)

• Connections to a PLC are handled by a connection pool, if use_pool is set to true, which can grow and shrink as needed. (This is especially useful, when connecting to a PLC, that has limited connection resources) The number of Min and Max connection count can be set in faxe configuration. Defaults to 2 and 16.

Strings

A String is defined as a sequence of contiguous char (byte) addresses. For strings faxe uses a special syntax not found in step7 addressing: DB5.DBS7.4 would read 4 bytes starting at byte 7 of DB 5 and output a string value.

Note: Characters with an ascii value below 32 will be stripped from the char-sequence. Also for strings the above mentioned read-optimization will not be used.

---

Examples

|s7read() 
.ip('10.1.1.5')
.rack(0)
.slot(2)
.every(300ms) 
.vars(
    'DB1140.DBX4.0', 'DB1140.DBX4.1',
    'DB1140.DBX4.4', 'DB1140.DBX4.5'
    )

.as(
    'data.tbo[1].ix_OcM1', 'data.tbo[1].ix_OcM2',
    'data.tbo[1].ix_Lift_PosTop', 'data.tbo[1].ix_Lift_PosBo'
    )

Read 4 values (BOOL in this case) from a plc every 300 milliseconds and name them with a deep json path.

def db_number = 1140
def db = 'DB{{db_number}}.DB'
|s7read()  
.ip('10.1.1.5')
.as_prefix('data.tbo.') 
.vars_prefix(db)
.vars(
    'X4.0', 'X4.1',
    'X4.4', 'X4.5'
    )

.as(
    'ix_OcM1', 'ix_OcM2',
    'ix_Lift_PosTop', 'ix_Lift_PosBo'
    )

Use of as_prefix and vars_prefix. The node will not read data on its own, because it has no every parameter. instead reading is done on data input from another node.

|s7read()
.ip('10.1.1.5')
.rack(0)
.slot(2)
.every(300ms) 
.vars('DB12004.DBS36.30')
.as('data.LcBc')

Read a sequence of 30 bytes as a string.

def db_number = 1140
def db = 'DB{{db_number}}.DB'
|s7read()
.ip('10.1.1.5')
.as_prefix('data.tbo.') 
.vars_prefix(db)
.byte_offset(4)
.vars(
    'X0.0', 'X0.1',
    'X0.4', 'X0.5'
    )

.as(
    'ix_OcM1', 'ix_OcM2',
    'ix_Lift_PosTop', 'ix_Lift_PosBo'
    )

In the last example byte_offset of 4 is used, so effectively the following addresses will be used: X4.0, X4.1, X4.4, X4.5

---

since v0.19.5

When as is not given, every second entry in vars is used as a field-name instead.

def db_number = 1140
def db = 'DB{{db_number}}.DB'
|s7read()
.ip('10.1.1.5')
.as_prefix('data.tbo.') 
.vars_prefix(db)
.byte_offset(4)
.vars(
    'X0.0', 'ix_OcM1',
    'X0.1', 'ix_OcM2',
    'X0.4', 'ix_Lift_PosTop',
    'X0.5', 'ix_Lift_PosBo'
    )

Parameters

Parameter	Description	Default
ip( string )	ip address of plc
port( integer )	network port	102 (standard s7 port)
every( duration )	time between reads	undefined
align( is_set )	align read intervals according to every	false (not set)
slot( integer )	plc slot number	1
rack( integer )	plc rack number	0
vars( string_list )	list of s7 addresses ie: 'DB3.DBX2.5' (see table below)
as( string_list )	output names for the read values Since 0.19.5: if not given, every second entry in vars is used as a fieldname (prefixes can still be used)	undefined
vars_prefix( string )	vars will be prefixed with this value	undefined
as_prefix( string )	as values will be prefixed with this value	undefined
byte_offset( integer )	offset for addressing, every address in vars gets this offset added	0
diff( is_set )	when given, only output values different to previous values	false (not set)
use_pool ( bool )	whether to use the built-in connection pool	from config value
optimized ( bool )	whether to use the collected read optimization or do standalone reading for this node	from config value

Note that params vars and as must have the same length (if both are given).

Data addressing

Note: Step7 style preferred and should be used !

Address	Step7 equivalent	Description
DB5,X0.1	DB5.DBX0.1	Bit 1 of byte 0 of DB 5
DB23,B1 or DB23,BYTE1	DB23.DBB1	Byte 1 (0-255) of DB 23
DB100,C2 or DB100,CHAR2	DB100.DBC2	Byte 2 of DB 100 as a Char
--	DB42.DBSINT36 or DB42.DBSI36	Signed 8-bit integer at byte 36 of DB 42
--	DB42.DBUSINT5 or DB42.DBUSI5	Unsigned 8-bit integer at byte 5 of DB 42 (equivalent to BYTE)
DB42,I3 or DB42,INT3	DB42.DBI3 or DB42.DBINT3	Signed 16-bit integer at byte 3 of DB 42
DB57,WORD4	DB57.DBW4	Unsigned 16-bit integer at byte 4 of DB 57
DB13,DI5 or DB13,DINT5	DB13.DBDI5 or DB13.DBDINT5	Signed 32-bit integer at byte 5 of DB 13
DB19,DW6 or DB19,DWORD6	DB19.DBDW6	Unsigned 32-bit integer at byte 6 of DB 19
DB21,DR7 or DB21,REAL7	DB21.DBDR7 or DB21.DBR7	Floating point 32-bit number at byte 7 of DB 21
DB2,S7.10*	DB2.DBS7.10 (faxe only)	String of length 10 starting at byte 7 of DB 2
DB1100,DT8	DB1100.DBDT8 or DB1100.DT8	8 byte S7 DATE_AND_TIME format (DT) (UTC is assumed)
I1.0 or E1.0	I1.0 or E1.0	Bit 0 of byte 1 of input area
Q2.1 or A2.1	Q2.1 or A2.1	Bit 1 of byte 2 of output area
M3.2	QM3.2	Bit 2 of byte 3 of memory area
IB4 or EB4	IB4 or EB4	Byte 4 (0 -255) of input area
QB5 or AB5	QB5 or AB5	Byte 5 (0 -255) of output area
MB6	MB6	Byte 6 (0 -255) of memory area
IC7 or EC7	IB7 or EB7	Byte 7 of input area as a Char
QC8 or AC8	QB8 or AB8	Byte 8 of output area as a Char
MC9	MB9	Byte 9 of memory area as a Char
II10 or EI10	IW10 or EW10	Signed 16-bit integer at byte 10 of input area
QI12 or AI12	QW12 or AW12	Signed 16-bit integer at byte 12 of output area
MI14	MW14	Signed 16-bit integer at byte 14 of memory area
IW16 or EW16	IW16 or EW16	Unsigned 16-bit integer at byte 16 of input area
QW18 or AW18	QW18 or AW18	Unsigned 16-bit integer at byte 18 of output area
MW20	MW20	Unsigned 16-bit integer at byte 20 of memory area
IDI22 or EDI22	ID22 or ED22	Signed 32-bit integer at byte 22 of input area
QDI24 or ADI24	QD24 or AD24	Signed 32-bit integer at byte 24 of output area
MDI26	MD26	Signed 32-bit integer at byte 26 of memory area
ID28 or ED28	ID28 or ED28	Unsigned 32-bit integer at byte 28 of input area
QD30 or AD30	QD30 or AD30	Unsigned 32-bit integer at byte 30 of output area
MD32	MD32	Unsigned 32-bit integer at byte 32 of memory area
IR34 or ER34	IR34 or ER34	Floating point 32-bit number at byte 34 of input area
QR36 or AR36	QR36 or AR36	Floating point 32-bit number at byte 36 of output area
MR38	MR38	Floating point 32-bit number at byte 38 of memory area