Specifications

The measurements were made with a PCS 095 in synchronous operation while the

following data are displayed:

8 consecutive double word variables

8 non-consecutive DW variables.

1 word variable

no variable

Key → LED [seconds]

(the programmable controller scan time must be counted)

Baud rate Port 8 DW flush 8 DW non flush 1 word 0 word

19200 1 0.26 0.42 0.24 0.21

19200 2 0.50 0.80 0.35 0.28

9600 1 0.46 0.72 0.40 0.37

9600 2 1.05 0.67 0.60 0.53

C.2.1 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.

PLC handling software