User`s manual

GFK-2334A Chapter 3 PROFIBUS Master CPU Configuration 3-5

Using Sync/Freeze Control

Sync and Freeze are global control functions used to synchronize remote I/O stations. You can use

these functions to cause a group of slaves to operate at the same time in your system.

■ The Sync command is used to control a slave’s outputs. When a slave receives a Sync

command, it holds the last output data from the master until the slave receives another sync

command from the master.

■ Freeze is used to control a slave’s inputs. When a Freeze command is sent to a slave, the

slave freezes its current inputs and does not update the inputs with new data until it receives

another Freeze command.

The use of the Sync/Freeze control word is optional. However, it must be assigned a

starting reference address, which is defined in the PROFIBUS configuration parameters.

The Sync/Freeze control word can be assigned to any PLC memory area and has a

length of either 16 bits if in discrete PLC memory (%Q, %I, %T, %M, %G) or one word if in

Word memory (%AI, &AQ, %R). The default is the first available address in %Q.

To use the Sync/Freeze control, you must specify a Group Select and a Command.

Sync/Freeze Control Word

Bits Name Description

0—7 (LSB) Group

Select

Specifies which group of slaves to send this command to. Each slave

can be in one or more groups (0 through 7), which are selected on

the Parameters tab of the slave Properties dialog box.

The Group ID is a bit mask of the Group ID locations. The LSB

corresponds to Group ID 0 and the MSB corresponds to Group ID 7.

8—15 (MSB) Command The command can be one of the following (HEX):

UNFREEZE = 0x04

FREEZE = 0x08

UNSYNC = 0x10

SYNC = 0x20

TRIGGER = 0x80*

* The most significant bit is used to trigger the command to be sent.

Note: The trigger operation occurs on both the 0 to 1 and 1to 0 transitions of the Trigger

bit.

Example

If you wanted to send a SYNC command to all the slaves with group ID 04, you would

write 0x10 to the LSB (which sets bit 4 of the Group Select byte) and write 0x20 to the

MSB.

To send this command, toggle the trigger bit of the Command byte (bit 15).