4-14
CM35 Counter Module
(4) J31069-D0416-U001-A5-7618
4.3.3
I/O Write Accesses
When I/O write accesses (T PQW) are used, it is essential to remember that
write accesses to the same I/O addresses
may overwrite each other before
being transferred to the CM35.
Example, pulse counter:
Start channel 1, then start channel 4 shortly afterwards
L
W#16#
01
81
// Start channel 1
T
PQW 258
// Module start a2
:
:
:
L
W#16#
08
81
// Start channel 4
T
PQW 258
// Module start a2
If the time between the start of channel 1 and channel 4 is too short, the start
command for channel 1 may be overwritten by the start command for chan-
nel 4.
This is particularly apt to happen if you are using distributed connection of
the CM35 with low bus transmission rates. In this case, the 1st start com-
mand (channel 1) is overwritten by the 2nd start command (channel 4) before
the 1st start command can be sent to the module via PROFIBUS.
The following measures should be taken to ensure that I/O write accesses do
not compete at the same address.
S
The same I/O address may only be write--accessed once during one OB1
cycle.
S
When a distributed layout is used, the DP cycle should be at least twice as
fast as the CPU cycle (DP cycle and CPU cycle can be determined with
STEP 7).
Data Communication with the CM35
Summary of Contents for SIMATIC CM35
Page 1: ...SIMATIC Counter Module CM35 Manual Release 06 2000 ...
Page 9: ...vi CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Table of Contents ...
Page 10: ...1 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Product Overview 1 ...
Page 20: ...2 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Function Description 2 ...
Page 23: ...2 4 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Function Description ...
Page 47: ...3 24 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Commissioning ...
Page 48: ...4 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Data Communication with the CM35 4 ...
Page 70: ...5 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Pulse Counter Operating Mode 5 ...
Page 98: ...7 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Timer Operating Mode 7 ...
Page 112: ...8 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Positioning Operating mode 8 ...
Page 131: ...8 20 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Positioning Operating mode ...
Page 133: ...A 2 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Literature ...
Page 134: ...B 1 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 EC Declaration of Conformity B ...
Page 135: ...B 2 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 EC Declaration of Conformity ...
Page 141: ...Glossary 6 CM35 Counter Module 4 J31069 D0416 U001 A5 7618 Glossary ...