Communication / USS
02.2004
6SE7087-6QX70 (Version AD) Siemens AG
8.1-10
Compendium Motion Control
SIMOVERT MASTERDRIVES
8.1.2
The structure of net data
Information which, for example, a SIMATIC S5 control unit (= master)
sends to a drive (= slave) or the drive sends to the control unit is placed
in the net-data area of each telegram.
8.1.2.1
General structure of the net-data block
The net-data block is divided into two areas:
♦
the PKW (parameter ID value) range
♦
the PZD (process data) range
The structure of the net data in the USS-protocol telegram is shown
below.
Protocol frame
STX
LGE
ADR
Net data
Parameter
(PKW)
Process data
(PZD)
BCC
PKW:
Parameter ID value
(parameter area)
PZD:
Process data
(process-data area)
♦
The
PKW area
relates to the handling of the parameter ID value
(PKW) interface. The PKW interface is not a physical interface but a
mechanism which handles parameter transfer between two
communication partners (e.g. control unit and drive). This involves,
for example, reading and writing parameter values and reading
parameter descriptions and associated texts.
All tasks which are performed via the PKW interface essentially
involve operator control and visualization, service and diagnosis.
♦
The
PZD area
contains the signals required for the
automation
system:
•
Control word(s) and setpoint(s) from the master to the slave
•
Status word(s) and actual value(s) from the slave to the master.
PKW area
PZD area
PKE
IND
PKW elements
PZD1
• • •
PZD16
Variable length
Variable length
The two areas together make up the net data block. This structure
applies to telegrams from the master to the slave and vice versa.
Introduction
Telegram structure
Structure of the
PKW and PZD areas
