PROFINET RT device interface (X101, X102)
PROFINET communication takes place via the switched Ethernet interfaces X101 and X102. IP addressing or PROFINET name resolution is carried out via the DIP switches. The IP address cannot be registered in the operating system. Therefore, all other services except PROFINET are not possible via this interface.
Fig.4: PROFINET RT device interface (X101, X102).PIN | Signal | Description |
|---|---|---|
1 | TD + | Transmit + |
2 | TD - | Transmit - |
3 | RD + | Receive + |
4 | connected | reserved |
5 | ||
6 | RD - | Receive - |
7 | connected | reserved |
8 |
Gigabit switch: Configuration and loss-free data transmission
The CX7293 Embedded PC has an integrated 2-port Ethernet Switch that supports data transfer rates of 10/100/1000 Mbit/s.
The baud rate of each port can be set to a fixed value via PROFINET. Autonegotiation is active by default. The switch uses the Cut-Through method to transmit frames with minimal latency.
For optimum performance, both ports should be operated at the same baud rate. At different speeds, the switch automatically adapts to the store-and-forward method. To avoid frame loss, it is advisable to adjust the data rate to a lower speed in this case.
First example: Different baud rates with data loss
- Port 1: 100 Mbit/s
- Port 2: 1000 Mbit/s
An industrial PC connected to port 2 sends large amounts of data to an industrial PC connected to port 1 of the switch. Due to different port speeds, the switch cannot operate in Cut-Through mode and must buffer the frames. However, the buffer capacity (e.g. in the EL6633) is not sufficient for the amount of data generated.
Result: Frames are discarded → retries by the protocol → increased network load → lower overall performance.
Second example: Different baud rates without problems
A pure PROFINET network without additional Ethernet services:
- Port 1: PROFINET controller with 100 Mbit/s
- Port 2: PROFINET devices with 1000 Mbit/s
As the data is transferred from the slower (100 Mbit/s) to the faster (1000 Mbit/s) network segment - i.e. from the PROFINET controller to various PROFINET devices - there are no bottlenecks. The network load is already limited by the 100 Mbit/s segment. Example: A utilization of 25% at 100 Mbit/s corresponds to only 2.5% utilization on the gigabit side.
Setting a fixed baud rate
The baud rate is set via the PROFINET controller in the manufacturer's project engineering tool. The "Adjustable MauType" function must be supported for this; the manufacturer of the PROFINET controller should be checked to see whether this is the case.
- The setting requires active PROFINET communication
- When setting for the first time, the link can be briefly interrupted (restart of the Ethernet port)
- The baud rate is retained after the restart
- 10 Mbit/s is only available via autonegotiation
Recommendation: Keep the default setting Autonegotiation.
Port 1 (Mbit/s) | Port 2 (Mbit/s) | Transmission direction | Procedure | Possible effects | Recommendation |
|---|---|---|---|---|---|
100 | 100 | both directions | Cut-Through | Optimum performance, no buffering problems | OK |
1000 | 1000 | both directions | Cut-Through | Optimum performance, no buffering problems | OK |
100 *) | 1000 | 100 → 1000 | Store-and-Forward | No bottlenecks, load is limited by the slower port | OK |
1000 | 100 | 1000 → 100 | Store-and-Forward | Buffer overflow possible → frame losses → higher network load | Adjust speeds or limit data rate |
10 | variable | both directions | Autonegotiation required | Very low speed, potential bottleneck | Not recommended |
variable | 10 | both directions | Autonegotiation required | Very low speed, potential bottleneck | Not recommended |
*) The PROFINET controller is connected to Port 1 (possibly via additional switches). Note: This configuration applies only when PROFINET is used exclusively; no other protocols.