AEG 381 D Specifications download pdf (Page 40)

Warning!

Check the PCS function and also after parameterization and/or driver

installation. All parameterized functions must be examined. Otherwise

malfunctioning of the PCS and/or programmable controller are possible.

The used MODBUSPS driver is a direct driver, i.e. it replaces directly the data

words between programmable controller and PCS. Either a small or no program-

mable controller program is required for that resulting only in a small scan time

burden for the programmable controller. Using the MODBUS 1 protocol, the pro-

grammable controller and the PCS communicate via RS-232C with 19200 or 9600

bauds and 8 data bits. It is possible to run a synchronous or asynchronous com-

munication operation since only the exact data words which are absolutely

necessary are replaced. During communication, the PCS is the master and the

programmable controller the slave. Thus, only one point-to-point connection is

possible for the interconnection.

SYNC or NOSYNC?

Since the data interchange occurs asynchronously by writing and reading via

several programmable controller cycles, the data written by the programmable

controller can be overwritten by the PCS and conversely. Thus, there is no data

consistency. Possible solutions are either a strict separation of read and write data

words (→ NO SYNC) or the usage of a synchronization word (→ SYNC). The usage

of a synchronization word enables the application of a time-out timer on the PCS

side.

At a CPU Stop, the communication is not interrupted. This CPU state can only be

detected in the sync. operation via the time-out timer.

DETERMINE THE DATA AREA

A common data area must be defined to enable access of the programmable

controller and the PCS. This area must be physically available and defined in the

programmable controller.

In the PCS, this area is defined via the AL and AM driver variables. If this area is

incorrectly selected in the programmable controller then a time-out can appear

during the operation!

EFFECTIVE RESPONSE TIMES: PCS - PROGRAMMABLE CONTROLLER

The response time of the protocol depends extensively on the tasks executed in the

PCS. If variables are displayed or even processed, then the communication cycle

time is essentially higher than with text without variables. Also, the transfer of the

message bit area and LED words influences this time. Limit these transfers. You

can do this also in the running operation, e.g. to realize a key-driven jog operation.

The following table presents a reference for the speed of the communication. The

so-called key → LED time is measured. That means the time in which a key is

transferred to the programmable controller and an LED is set in the PCS. This time

is made up of 2 communication cycles and a programmable controller scan time.

The response time, i.e. the time a key is signaled in the programmable controller

is only half the indicated time!

PLC handling software

C.2. PLC handling software

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AEG 381 D Specifications Page 40

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