HEIDENHAIN MANUALplus 620 Technical Manual page 1518

8.4 Operands
8.4.1 Overview of operands
Operand Abbreviation
Marker M (marker)
Input I (input)
Output O (output)
Counters C (counter)
Timer T (timer)
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The symbolic PLC operands that are predefined by HEIDENHAIN for the API
3.0 symbolic programming interface are listed in Chapter 5 (see "Overview of
the PLC Operands" on page 604).
Address range
M0 to M9999
M0 to M999 are free; they are deleted only after entering
the code number 531210, not during a reset (nonvolatile
range); the range can be reduced in the *.CFG file of the
PLC compiler.
M1000 to M3999 are free; they are deleted during reset.
M4000 to M5999 are reserved for the NC-PLC interface if
you are using the old TNC-API. (M4800 to M4999 are
deleted before the first run of the PLC program, e.g. after
compilation or restarting).
They are freely usable if you are using the new symbolic
API.
M6000 to M9999 are free; they are deleted during reset.
I0 to I999
Maximum 8
C input/output systems (PL 6xxx) are allowed in the HSCI
system, and of these, one PL 62xx or one UEC 11x system
PL.
Inputs are assigned to symbolic operands using the PC
software IOconfig.
O0 to O999
A maximum of 8 external PLC input/output systems (PL
6xxx) are allowed in the HSCI system, and of these, one PL
62xx or 1 UEC 11x system PL.
Outputs are assigned to symbolic operands using the PC
software IOconfig.
Start counter: C0 to C47
Counter contents: C48 to C95
Counter pulse release: C96 to C143
Timer start: T0 to T47
Timer is running: T48 to T95 and T96 to T999
HEIDENHAIN Technical Manual MANUALplus 620