Specifications

D-6

D Buep 19e-Direct driver

The BOSMULPS communication block is located on the BOSCH floppy

disk. The effective response time speed between PLC and PCS depends

on the baud rate, the used interface, and the data volume. E.g. the SK

interface is therefore approx. 50% slower than the direct CPU interface.

• Access types

The used B19EDIR driver is a direct driver i.e. it exchanges data

words between the PLC and the PCS directly. No or just a small PLC

program is required. Therefore, the scan time in the PLC is only

slightly loaded.

• SYNC or NOSYNC

Since the data interchange occurs asynchronous via several PLC

writing and reading cycles, data written by the PLC can be overwritten

by the PCS and conversely. Thus, a data consistency is not given.

Possible solutions are either a strict separation of read and write

data words (-> NO SYNC) or the use of a synchronization word (->

SYNCS). The use of a synchronization word enables the use of a

timeout timer on the PCS side.

D1.1 Asynchronous communication

• Preset value and actual value data words must be strictly separated

(write accesses can disturb each other). Even then, for example the

reading of a variable which extends across several data words can

result in an error at the time when the variable is read although only

a part of it has been written.

• Bit variables should be used only 1 time per word since the access

of the PCS occurs only word-by-word. A word fetched by the PCS

which is changed and written back can overwrite another bit varia-

ble in this word. This applies also for the message bit area in delete

behavior 2 (resetting of the bit in the PLC).

• Timeout monitoring is possible only in the PLC. To implement this

function, the PCS sends a count word which is incremented by 1 in

each communication cycle in the 3rd word. The use of the timeout

timer is described in the handling software.

Advantages in comparison to the SYNC operation are:

• A faster data interchange. The scan time of the PLC does not influence

the calculation of the response time.

• No program is needed in the PLC for communicating. Only the word

area with the correct size must be available. Access to the word

area in the PLC program must be possible at any time.