Siemens EF 83H Series Manual do Utilizador descarregar pdf (Página 56)

Communication Services

4-5

SIMATIC 505 PROFIBUS-FMS CP User Manual

These

bits are used to synchronize (handshake) communication between the

user program and the FMS CP module during communication jobs.

• Th

e Job Start Bit is a user

-selected bit in one of the available output

words (WY) assigned to the FMS CP module. The Job Start bit is used

in the user program to trigger a data transfer job. The FMS CP module

must see a 0 to 1 transition on the Job Start Bit to begin a data

transfer job.

•

The Job Active Bit is a corresponding bit in the input word (WX) set by

the FMS CP module. The Job Active bit signals that a requested data

transfer job is in progress. When this bit goes back to 0, the controller

knows that the job has been completed and can then initiate another

job by setting the corresponding WY bit to 1.

•

The bits in the first three output words assigned to the FMS CP module

are available as the Job Start Bits. In this example, any of the 48 bits

in WY5, WY6, and WY7 can be used as the Job Start Bit for a job as

needed. The corresponding bit in WX1, WX2, or WX3 (the Job Active

Bit) signals a job in progress.

The handshaking, or synchronizing, of a job such as the one shown in

Figure 4-1 can be summarized as follows:

1. W

ith the WY bit set to 0, the programmable logic controller must wait

for the corresponding WX bit to become 0 before a job can be initiated.

The controller sets the WY bit from 0 to 1 to trigger the job.

The FMS CP module registers the rising edge on the WY bit, sets the

corresponding WX bit to 1, and starts the job.

NOTE: For a job to execute, the FMS CP module must see the transition of

the WY job start bit. Either a reset of the FMS CP module, or a power cycle

of the entire programmable logic controller base, may result in the ladder

logic program setting a WY job start bit prior to the FMS CP module

recovery

. When this condition occurs, the FMS CP module does not execute

the job.

A timer instruction (TMR or TMRF) may be implemented in the controller

The timer is enabled when the WY job start bit is set. The timer is reset in

response to the WX job active bit. If the WX job active bit never responds to

a WY job start bit, the timer is allowed to time out and clears the current

WY job active bit. The next execution of the ladder logic starts the WY job

start bit under normal operating conditions. T

o allow ample FMS CP

module startup time, set the timer preset value to 30 seconds.

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