AEG 381 D Specifications download pdf (Page 27)

B2.1 Asynchronous Communication

 Actual and preset value data words must be strictly separated (writing accesses

can interfere). Even then, e.g. the reading of a variable which extends across several

data words can result in a fault and of course then, if the variable is read although

only a part of the variable has been written.

 Bit variables should be used only once per word since the access of the PCS

occurs only word-by-word. A word that has been retrieved, changed, and written

back by the PCS can overwrite another bit variable using this word! This is also

valid for the message bit area with erase behavior 2 (deleting of the bit in the

programmable controller).

 Time-out monitoring is possible only in the programmable controller. Therefore,

the PCS sends one incremented count word in word 3 in each communication

cycle. The usage of a time-out timer is described in the handling software.

The advantages compared to the SYNC operation are:

 Faster data interchange. The programmable controller scan time is not taken

into account when calculating the response.

 There is no need for a communication program in the programmable controller.

Only the flag word area must be available having the correct size. Access to the

flag word area is possible at any time in the programmable controller program.

B2.2Synchronous communication

If you want to use the entire functional extent of the PCS, then the access to the

data in the programmable controller must be synchronized, i.e. programmable

controller and PCS access alternately. In addition, a synchronization word is

transferred to the programmable controller. PB2 examines this word and enables

the programmable controller user program access. If the user program is finished

with the processing of the data words, then the synchronization word is changed

and the PCS accesses the data area. While the PCS processes the data, the user

program may not access to the data. This Ping-Pong game offers the possibility to

realize a time-out monitoring also in the PCS. Whenever the PCS reads the inverted

synchronization word, the timer is restarted. If the timer expires then a time-out

exists.

Using this alternating access, actual and preset values can be mixed, bit varia-

bles used, erase behavior 2 realized, etc. Therefore, the entire intelligence of the

PCS is available. The disadvantage for you is that the reaction speed between

PCS and programmable controller is lowered. Furthermore, before accessing the

data, the programmable controller program must always scan whether access is

allowed or not.

The time-out time, i.e. the time that passes since the last writing of DW3 up to the

time-out message in the programmable controller, should be set to a minimum of

2 seconds. In the PCS, the time-out time is set via the AA driver variable or

COM_TIMEOUT.

Programmable controller handling software

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AEG 381 D Specifications Page 27