The s7read node

Read data from a siemens s7 plc via the snap7 library using the iso on tcp 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.

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

• 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.

Note: data transfer size is limited to 128 bytes.

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

Parameters

Note that params vars and as must have the same length.

Data addressing

Note: Step7 style preferred and should be used !