S5 AS511 protocol 点击：497 | 回复：1
发表于：2007-10-28 16:50:00
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------------------------------------------------------------------
SIEMENS SIMATIC S5 AS511 (Programming port) protocol description
Last reviewed: May 4, 1999
- corrected a DLE/ACK sequence in DBWrite function
- provided new informations on data synchronisation between AS511
interface and the CPU.
------------------------------------------------------------------
COM port setup
--------------
Siemens data frame is not usual, open your port with:
speed 9600 baud
data 8 bits
stop 1 bit
parity EVEN
DLE control character
---------------------
DLE (10hex) is a control character, used to inform the receiver that the
following byte is to be considered a control character and not a data byte.
In other words, DLE is a software switch within the AS511 protocol to divide
control and data bytes.
Whenever a DATA byte containing the value 10hex is to be sent, the sender must
DOUBLE the char. This means that to send a data byte 10hex, the sender must
send 10hex 10hex (DLE DLE).
The receiver must consider the thing, so a single DLE will mean a protocol
signal, while two consecutive DLE are to be interpreted as a SINGLE data byte
containing the 10hex value. This is a little tricky, since the receiver NEVER
knows exactly how many bytes to expect.
Communication breaks
--------------------
Take also note that the AG can answer DLE NAK instead of DLE ACK if the
requested operation can not be carried out.
In this case, the PG must abort the communication and wait for 500ms before
attempting a new communication.
The value of 500mS is also applied as timeout value in case of missing response
from the partner.This also means that no "holes" of 500mS (or more) are allowed
during a communication (e.g. within a DB_READ function)
Data addressing
---------------
To read or write a datablock value, you need to know its address in PLC memory.
Therefore you must invoke B_INFO function to know the address, then you can
call DB_READ or DB_WRITE by giving the initial and final address of the area to
be read or written.
Be aware that when the datablock is rewritten in CPU (or after a program
compression), its address in PLC memory changes.
Therefore when communicating with double-port CPUs (or H1 networked CPUs) you
must take care of it, since the PLC program may be unexpectedly modified by
somebody else via other interfaces.
MOTOROLA and INTEL byte order conversion
----------------------------------------
Be aware that in SIMATIC the LSB/MSB bytes order is reversed:
SIMATIC:
15..............0
BYTE 0 BYTE 1
INTEL:
15..............0
BYTE 1 BYTE 0
To obtain the correct integer value of a dataword on INTEL processors, the user
must therefore:
- swap the received bytes
and
- swap the bytes before sending them to the PLC
Data synchronisation
--------------------
The AS511 protocol is NOT synchronized with the CPU scan cycle.
This means that data transmitted by a computer can drop in the PLC
memory at any time during the PLC program scan..
If the program is reading some data (such as a recipe), there is
no guarantee that all data is "fresh received".
The best solution is to send recipe data in two steps:
a) send all the recipe data, then
b) send a "data ready" code in a further DataWord.
The PLC program, when receives the "data ready" code, will read all the
recipe data and clear the "data ready" info.
In this way you are sure to accept the recipe data only when it has been
completely transmitted to the PLC memory.
/////////////////////////////////////////////////////////////
SIEMENS SIMATIC S5 AS511 (Programming port) protocol description
Last reviewed: May 4, 1999
- corrected a DLE/ACK sequence in DBWrite function
- provided new informations on data synchronisation between AS511
interface and the CPU.
------------------------------------------------------------------
COM port setup
--------------
Siemens data frame is not usual, open your port with:
speed 9600 baud
data 8 bits
stop 1 bit
parity EVEN
DLE control character
---------------------
DLE (10hex) is a control character, used to inform the receiver that the
following byte is to be considered a control character and not a data byte.
In other words, DLE is a software switch within the AS511 protocol to divide
control and data bytes.
Whenever a DATA byte containing the value 10hex is to be sent, the sender must
DOUBLE the char. This means that to send a data byte 10hex, the sender must
send 10hex 10hex (DLE DLE).
The receiver must consider the thing, so a single DLE will mean a protocol
signal, while two consecutive DLE are to be interpreted as a SINGLE data byte
containing the 10hex value. This is a little tricky, since the receiver NEVER
knows exactly how many bytes to expect.
Communication breaks
--------------------
Take also note that the AG can answer DLE NAK instead of DLE ACK if the
requested operation can not be carried out.
In this case, the PG must abort the communication and wait for 500ms before
attempting a new communication.
The value of 500mS is also applied as timeout value in case of missing response
from the partner.This also means that no "holes" of 500mS (or more) are allowed
during a communication (e.g. within a DB_READ function)
Data addressing
---------------
To read or write a datablock value, you need to know its address in PLC memory.
Therefore you must invoke B_INFO function to know the address, then you can
call DB_READ or DB_WRITE by giving the initial and final address of the area to
be read or written.
Be aware that when the datablock is rewritten in CPU (or after a program
compression), its address in PLC memory changes.
Therefore when communicating with double-port CPUs (or H1 networked CPUs) you
must take care of it, since the PLC program may be unexpectedly modified by
somebody else via other interfaces.
MOTOROLA and INTEL byte order conversion
----------------------------------------
Be aware that in SIMATIC the LSB/MSB bytes order is reversed:
SIMATIC:
15..............0
BYTE 0 BYTE 1
INTEL:
15..............0
BYTE 1 BYTE 0
To obtain the correct integer value of a dataword on INTEL processors, the user
must therefore:
- swap the received bytes
and
- swap the bytes before sending them to the PLC
Data synchronisation
--------------------
The AS511 protocol is NOT synchronized with the CPU scan cycle.
This means that data transmitted by a computer can drop in the PLC
memory at any time during the PLC program scan..
If the program is reading some data (such as a recipe), there is
no guarantee that all data is "fresh received".
The best solution is to send recipe data in two steps:
a) send all the recipe data, then
b) send a "data ready" code in a further DataWord.
The PLC program, when receives the "data ready" code, will read all the
recipe data and clear the "data ready" info.
In this way you are sure to accept the recipe data only when it has been
completely transmitted to the PLC memory.
/////////////////////////////////////////////////////////////
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