Programming Sequence - Siemens SIMATIC S7-200 System Manual

Using USS Protocol Instructions to Communicate with Drives
11.2

Programming Sequence

The programming sequence for using USS Protocol instructions is shown below.
1. Place the USS_INIT instruction in the user program. This automatically adds
several hidden subroutines and interrupt routines to the program. The
USS_INIT should only be called for one scan to initiate or change the USS
communication parameters. See page 11-5 for more information about the
USS_INIT instruction.
2. Assign a V memory address to the first location in the USS global symbol
table. All the other addresses are automatically assigned. A total of 400
consecutive bytes are required. See Figure 11-1 for the USS tab of the
Symbol Table.
3. Place only one DRV_CTRL instruction per active drive in your program. You
may add as many READ_PM and WRITE_PM instructions as you wish, but
only one of these may be active at a time.
4. Configure the drive parameters to match the baud rate and address used in
the program. Refer to the Drive Setup in Section 11.5.
5. Connect the communications cable between the CPU and the drives. It is very
important that any control equipment that is connected to the drive (such as a
PLC) is connected to the same ground or star point as the drive by using a
short, thick cable.
Caution
!
Interconnecting equipment with different reference potentials can cause unwanted
currents to flow through the interconnecting cable.
These unwanted currents can cause communication errors or damage equipment.
Be sure all equipment that you are about to connect with a communication cable
either shares a common circuit reference or is isolated to prevent unwanted
current flows. See "Grounding and Circuit Reference Point for Using Isolated
Circuits" in Section 2.3.
The shield must be tied to chassis ground or terminal 1 on the 9-pin connector. It
is recommended that you tie terminal 2-0V on the MicroMaster drive to chassis
ground.
Note
If you cannot read all the variables on the USS instruction blocks, select
View Zoom from the menu and then increase the grid width.
11-4
S7-200 Programmable Controller System Manual
A5E00066097-02