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IP 240
11
Direct Data Interchange with the IP 240
For time-critical applications, it may be necessary to exchange data directly with the IP 240
without using the control FBs. This section provides information on
•
data interchange with the IP 240.
•
the job numbers you must specify so that
-
the IP will provide the data you need,
-
the IP will accept new data.
•
the contents of the transfer buffer on the IP 240 in position decoding and counting mode.
The contents of the transfer buffer for positioning mode are discussed in Chapter 10. In IP 252
expansion mode (S5-115U only), the two IPs interchange data autonomously following con-
figuring, making an interchange between the S5 CPU and the IP 240 unnecessary.
A 16-byte address space is provided for data interchange with the IP 240. The absolute addresses
of the individual bytes are a composite of the module start address and an offset of between 0
and 15.
Absolute address=module start address+offset
The address space is subdivided as follows:
Offset 0 to14
With offsets 0 to 14 you address the individual
bytes in the transfer buffer. The S5 CPU can
read from and write to this buffer.
S5 CPU and IP 240 both have bidirectional data interchange capabilities. The following functional
sequences must be observed:
S5 CPU IP 240
Write new, modified data
to the IP 240
To issue a Write request, you must first enter
the new data in the transfer buffer, then
specify a job number which tells the IP 240 to
fetch the data.
Note
In order to prevent excessive variations in the IP 240's response time, the IP 240
firmware permits only one data interchange per firmware cycle.
Once new data has been transferred to the IP 240, no further interchanging of data
is permitted in the next firmware cycle.
EWA 4NEB 811 6120-02a
Direct Data Interchange with the IP 240
Offset 15
With offset 15 you address:
•
the status register, which can be read by
the S5 CPU and provides information on
the servicing job requests on the IP 240.
•
the job request register, to which the
S5 CPU has write access, to specify the job
number.
S5 CPU IP 240
Read current data from
the IP 240
To issue a Read request, you must specify a job
number indicating which data are to be read.
The IP 240 then makes this data available in
the transfer buffer, and you can read it out
from there.
11-1
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