BECKHOFF C1120 User Manual

Page 17

C1120 S5 to II/O Lightbus Interface

Beckhoff II/O-Lightbus System

Date 27.06.97

Version 2.1

Page 17 of 52

Arbitration of a single load /transfer of peripherial bytes

As used with the indirect communications list every module in the II/O Lightbus System can
be accessed immediately via a single communication list: The IDENT- number of a dedicated
module has to be placed in the first address block address location, following four bytes keep
the I/O data.
For handshake purposes two bits in the Status Byte of the PLC can be used: PB/PY254 and
PB/PY 255 Bit 0:
First, IDENT number and I/O data are written to the single communication list. Then, bit 0 of
PB/PY 254 is set (strobe bit) by the PLC. After this, a transfer to PB PY 255 with any data
forces an interrupt and II/O Lightbus communication with the C1120 interface.
The C1120 interface card responds with setting the bit 0 of PB/PY 254 (ACK bit): the data
byte contents are valid and can be read by the PLC with L PB. The PLC handshakes with
resetting the bit 0 of PB/PY 254 (strobe bit). The C1120 ends the handshake cycle by resetting
the ACK bit 0 of PB/PY 254.
By setting "address single communication" to 0 in the setup screen, this option is not
supported during the use with this setup.

Example :
The value of the single communication address is set to 128.

C1120

1.)

Transfer identnumber for dedicated
II/O-Lightbus module address to
PB/PY 128

2.)

Transfer transmit data from memory
flags or equiv. to PB/PY 129,130, 131,
132

3.)

Set strobebit
L

PB/PY 254

4.)

Force interrupt on C1120: transfer
something to PB/PY255
L

AFFE

255

5.)

Polling of ack- bit in statusregister

II/O-Lightbus communication doing
transfer to and from the module

6.)

Set of Ack.- bit in statusregister

7.)

Load of valid data from the single
communication list to destination
L

8.)

Reset strobebit
Polling of ack- bit in statusregister

9.)

Reset of Ack.- bit in statusregister