Frequently Asked Questions for S7-300（1）

Last Updated on 2017-09-08 Hits:1451

1: How should I avoid the "communication failure" message when using the CPU 315F and ET 200S?
With the CPU S7 315F, ET 200S, and fail-safe DI / DO modules, you will call the OB35 fail-safe program. Also, you have accepted the default settings for all monitoring times and are willing to receive the "communication failure" message. OB 35 is set to 100 milliseconds by default. You have set the F monitoring time of the F I / O module to 100 milliseconds so that the I / O module is addressed at least once every 100 milliseconds. However, since the OB 35 is called every 100 milliseconds, a communication failure occurs. To ensure that the scan interval of the OB35 differs from the F monitoring time, make sure that the F monitoring time is greater than the scan interval of OB35.
S7 distributed security system, until the V5.2 SP1 and 6ES7138-4FA00-0AB0,6 ES7138-4FB00-0AB0,6ES7138-4CF00-0AB0 will appear this problem. In the new module, the F monitoring time is set to 150 milliseconds.
2: What is the monitoring time of S7-300 CPU on PROFIBUS when DP slave is not available?
When operating the PROFIBUS network on a DP slave on the PROFIBUS interface of the CPU, it is desirable to check if the desired configuration matches the actual configuration during startup. Two different times are given on the Startup tab in the CPU Properties dialog box.
3: how to determine the power supply or buffer error, such as: battery failure?
If an event is triggered by a power supply (only S7-400) or one of the buffers, the CPU operating system accesses OB81. After error correction, re-visit OB81. In the case of a battery failure, if the BATT.INDIC switch in battery detection is active, the S7-400 only accesses OB81. If OB81 is not configured, the CPU does not enter the operating state STOP. If OB81 is not available, the C PU remains running when the power supply fails.
4: What should I pay attention to when I / O modules (centralized or distributed) on an S7 CPU are assigned addresses?
Note that the created data area (such as a double word) can not be configured on the boundary of the process image because only the area below the boundary can be read into the process image in the data block, so it is not possible to access from the process image data. Thus, these configuration rules do not support this situation: for example, an input double word is configured on the 254 address of a 256-byte input process image. If such a location is required, the size of the process image must be adjusted accordingly (in the Properties of the CPU).
5: How to communicate the global data in the S7 CPU? What should I pay attention to when communicating?
Global data communication is used to exchange small volume data, global data (GD) can be:
Input and output
Mark
Data in the data block
Timer and counter functions
Data exchange refers to exchanging data in the form of packets between CPUs connected to a one-way or two-way GD ring. The GD ring is identified by the GD ring number.
One-way connection: a CPU can send GD packets to multiple CPUs.
Two-way connection: connection between two CPUs: Each CPU can send and receive a GD packet.
It is necessary to ensure that the receiving end CPU does not acknowledge the reception of global data. If you want to exchange data via the corresponding communication block (SFB, FB or FC), you must connect the communication blocks. By defining a connection, the design of the communication block can be greatly simplified. This definition is valid for all calls that are called and do not need to be redefined each time.
6: Can I use an S7-400 memory card for CPU 318-2DP?
In normal operation, only "short"> memory cards with order numbers 6ES7951-1K ... (Flash EPROM) and 6ES7951-1A ... (RAM) can be used.
7: Why does the CPU 31xC not read the full input from the default addresses 124 and 125, although the LED is lit?
For the following models of CPU, check that the 24V voltage is connected to pin 1. The LED is controlled by the input current. The 24V voltage on pin 1 needs to be further processed.
313C (6ES7 313-5BE0.-0AB0), 313C-2DP (6ES7 313-6CE0.-0AB0), 313C-2PTP (6ES7 313-6BE0.-0AB0), 314C-2DP (6ES7 314-6CF0.-0AB0) 314C-2PTP (6ES7 314-6BF0.-0AB0)
8: When configuring the CPU 31x-2 PN / DP PN interface, what happens when the PROFINET interface occasionally has a communication error?
Make sure that all components (conversions) in Ethernet (PROFINET) support 100 Mbit / s full duplex basic operations. Avoid the central distributor to split the network because these devices can only work in half-duplex mode.
9: What is the meaning of the "clock" correction factor in the hardware configuration editor?
In the hardware configuration, through CPU> Properties> Diagnostics / Clock, you can enter a "clock"> field to specify a correction factor. This correction factor only affects the hardware clock of the CPU. The time interrupt is derived from the system clock and has nothing to do with the hardware clock setting.
10: how to use PROFIBUS DP with the function block to achieve in the main and slave between the two-way data transfer?
The master station plc can complete the data exchange with the slave by calling SFC14 "DPRD_DAT" and SFC15 "DPWR_DAT", and FC1 "DP_SEND" and FC2 "DP_RECV" can be called for the slave to complete the exchange of data.
11: Which identification data can be read from the S7 CPU?
The following identification data can be read with SFC 51 "RDSYSST":
You can read the order number and the CPU version number. To do this, use SFC 51 and SSL ID 0111 and use the following indexes:
1 = module identification
6 = Basic hardware identification
7 = Basic firmware identification
12: How can the programmable communication function blocks FB14 ("GET") and FB15 ("PUT") be programmed for data exchange on the S7-300 with CPU 317-2PN / DP?
In order to exchange data between two S7-300 workstations using the CPU 317-2PN / DP via an S7 connection, where the S7 connection is configured using NetPro. <In the S7 communication, the communication function block must be called. The module FB14 ("GET") is used to fetch data from the remote CPU, and the module FB15 ("PUT") is used to write data to the remote CPU. The function blocks are included in the standard library of STEP 7 V5.3.
The attributes of the communication blocks FB14 ("GET") and FB15 ("PUT") of the CPU 317-2PN / DP are:
FB14 and FB15 are asynchronous communication functions. The operation of these modules may span multiple OB1 loops. Activate FB14 or FB15 by entering parameter REQ. DONE, NDR, or ERROR indicates that the job has ended. PUT and GET can communicate simultaneously through the connection.
Note: You can not use the communication blocks in the library SIMATIC_NET_CP for CPU317-2PN / DP.
13: What do you need to pay attention to for compact CPU 313C-2 PtP and CPU 314-2 PtP job synchronization?
In the user program, you can not program SEND jobs and FETCH jobs at the same time.
That is, the FETCH job (SFB 64) (even when REQ = 0) can not be called as long as the SEND job (SFB 63) is not completely terminated (DONE or ERROR). The SEND job (SFB 63) (even when REQ = 0) can not be called as long as the FETCH job (SFB 64) is not completely terminated (DONE or ERROR). When processing an active job (SEND job, SFB 63 or FETCH job, SFB 64), a passive job (SERVE job, SFB 65) can be processed at the same time.
14: Can the MICROMASTER 420 to 440 be run together with the CPU 317T as the configuration axis (position external detection)?
Yes, but in terms of power and accuracy, the requirements for the configuration shaft are very different. In the case of high demand, the servo drive SIMODRIVE 611U, MASTERDRIVES MC or SINAMICS S must be operated with the CPU 317T. In the low demand, MICROMASTER series can meet the power and accuracy requirements.
15: How do you configure direct data exchange (inter-node communication) between two CPU modules that have been configured as DP slaves?
The two CPU stations are configured as DP slaves and are operated by the same DP master. The communication between them is done by configuring the exchange mode as DX to complete the direct data exchange.
16: How do I use SFC65, SFC66, SFC67 and SFC68 to communicate?
For unidirectional basic communication, the system function SFC67 (X_GET) is used to read data from a passive station and the system function SFC68 (X_PUT) is used to write data to a passive station (server). These blocks are called only in the active station. For a bi-directional basic communication, call the system function SFC65 (X_SEND) in the station where the data is to be sent to another active station. In the same active active receiving station, the data will be recorded via the system function SFC66 (X_RCV).
Two types of basic communication, each block call can handle up to 76 bytes of user data. For S7-300 CPUs, the data consistency of data transfer is 8 bytes and is full for S7-400 CPUs. If you are connected to the S7-200, you must consider that the S7-200 can only be used as a passive station.
17: What is the free allocation of I / O addresses?
The free distribution of addresses means that you can freely assign an address to each module (SM / FM / CP). The address assignment is made in STEP 7. The start address is defined first, and the other address of the module is based on it.
Advantages of free allocation of addresses: Because there is no address gap between modules, you can optimize the use of available address space. When creating standard software, the configuration of the S7-300 is not taken into account during the assignment of addresses.
18: What can the diagnostic buffer do?
Faster identify the source of the fault, thus improving system availability. Evaluate the last event before STOP and look for the cause of STOP.
The diagnostic buffer is a circular buffer with a single diagnostic entry that is displayed in the event sequence; the first entry shows the most recent event. If the buffer is full, the earliest events will be overwritten by the new entry. Depending on the CPU, the size of the diagnostic buffer is either fixed or can be set via HW Config via parameters.
19: What does the entry in the diagnostic buffer include?
1) fault event
2) operating mode changes and other important operational events to the user
3) User-defined diagnostic event (with SFC52 WR_USMSG)
In operating mode STOP, the event is stored as little as possible in the diagnostic buffer so that the user can easily find the cause of the STOP in the buffer. Therefore, entries are stored in the diagnostic buffer only if the event requires the user to generate a response (such as scheduling the system memory reset, the battery needs to be charged) or must register important information such as firmware updates, station failures.
20: How do I determine the size of the MMC to store the STEP 7 project in its entirety?
In order to select the appropriate MMC for the project, you need to understand the size of the entire project and the size of the block to be loaded. You can determine the size of the project as follows:
1) Archive the STEP 7 project first. Then open the archived item in Windows Explorer and determine its size (select the item and right click). This will tell you the size of the archive.
2) Load the block into the CPU. You still need to select "PLC> Module Information> Memory". Here, in the "Load memory RAM + EPROM", you can see the size of the allocated load memory.
3) The value must be added to the size of the archived item that has been determined. This gives you the amount of total memory needed to save the entire project on an MMC.