QUESTION:
What should you watch out for when
accessing data of the distributed I/O in connection with CPU315-2
DP?
ANSWER:
Depending on the type of CPU 315-2DP you are
using (6ES7 315-2AFxx-0AB0 or 6ES7 315-2AG10-0AB0) there are
differences in the size of the address area available.
| Address area - user data |
6ES7
315-2AFxx-0AB0 |
6ES7
315-2AG10-0AB0 |
| Address area / CPU |
Byte 0 to 1023 |
Byte 0 to 2047 |
| In the PII/ PIQ |
Byte 0 to 127 |
Byte 0 to 127 |
| Consistent data |
32 bytes |
128 bytes |
| User data of a station |
244 bytes input / 244 bytes
output |
244 bytes input / 244 bytes
output |
Table 1: CPU data of the I/O
- Addresses that are greater than the address area of the CPU,
cannot be addressed either by load or by transfer commands and
cannot be addressed either by SFCs.
- If there is no consistency, then you must always
use load/transfer commands with CPU 315-2 DP (6ES7 2AFxx-0AB0). It
is not possible to use SFC14 and SFC15 here.
- With CPU 315-2DP (6ES7 315-2AG10-0AB0) you can also use system
functions SFC 14/15 to access areas with 1, 2 and 4 bytes. In doing
so however the complete consistent area has to be read/written. If
the area is 1 word with consistency over the entire length, then
with SFC 14/15 you can only read/write the whole word. If the area
is 1 word and has byte consistency, then with SFC 14/15 you can
read/write a length of both 1 byte and 1 word.
- If there is consistency and this is 3 bytes or more than 4
bytes (maximum permissible is 128 bytes, depending on the CPU),
then for CPU 315-2 DP (6ES7 2AFxx-0AB0) you are obliged to work
with SFC14 and SFC15. It is not possible to use
load/transfer commands.
For CPU 315-2 DP (6ES7 2AG10-0AB0) you should normally also use
SFC14 and SFC 15. However, it is possible to use load/transfer
commands on consistent areas in order to read or write just parts
of the consistent area.
- If there are consistent areas in the process image, then with
CPU 315-2 DP (6ES7 2AG10-0AB0) the consistent areas can also be
updated through the process image transfer, so that you don't need
SFC14/15 at all in such cases.
|
Consistency |
6ES7
315-2AFxx-0AB0 |
6ES7
315-2AG10-0AB0 |
| None |
Access via load/transfer
commands |
Access via load/transfer
commands
or also with SFC14/15 for lengths of 1, 2 or 4 bytes, or 1 or 2
words, or 1 double word |
| 1 byte |
Access via load/transfer
commands |
Access via load/transfer commands or
access via SFC 14/15 |
| 2 bytes |
Access via load/transfer
commands |
Access via load/transfer commands or
access via SFC 14/15 |
| 3 bytes |
Access via
SFC 14/15 |
Access via load/transfer commands or
access via SFC 14/15 |
| 4 bytes |
Access via load/transfer
commands |
Access via load/transfer commands or
access via SFC 14/15 |
| 4 - 128 bytes |
Access via
SFC 14/15 (1) |
Access via load/transfer commands or
access via SFC 14/15 |
(1) With CPU 6ES7 315-2AFxx-0AB0 a maximum of 32
bytes can be read/written consistently.
Table 2: Access rules
Keywords:
Consistent data
|
german
