slc 505 slow ethernet comms

I have a SLC 5/05 with really slow Ethernet comms. It is on a network with three Proface screens but comms is just as slow when I connect directly to the CPU. I have cleared bits S:2/15 and S:33/7 as suggested and this did improve the comms slightly but it is still very poor. I have tried different laptops, cables etc. Just wondered if anyone has experienced this before and how it was overcome?

Welcome to the forum!

Not sure how familiar you are with the SLC 500, but I recall that they don't have a separate processor to handle communications. Therefore, comms only get updated at the end of the program scan by default.

One way to get around this is to use the SVC (service communications) instruction. If you strategically place one, two or more of these in your ladder, your Ethernet and/or Serial communications will be processed more often. The online help file gives a good explanation of how to use this instruction.

Be aware that this comes at the cost of higher scan times. See what you can live with. I first became aware of this instruction when using a SLC 5/05 with three WonderWare stations. I can't remember how many SVC instructions I added, but placing them one at a time helped me figure out what the best balance was between scan time & HMI update rate.

Are you sure your Ethernet port speed/duplex settings are all correct? The Ethernet port on the 5/05 and and the switchport should have the same duplex/speed settings. I just ran into this the other day. I was having trouble communicating reliably to a SLC. The port statistics in the switch showed a lot of MAC transmit/receive errors, FCS and CRC errors.

The symptom was very slow communications with RSlogix 500, and slow response on the HMI, The speed/duplex mismatch causes lost packets and bottlenecks the connection with re-transmitted packets of which a sizable percentage will fail again.

Thanks for the advice. I have now solved this problem. The slow etherent comms is being caused by the way the the devicent is mapped in the ladder. Each M0/M1 is mapped accross individually. I found that by not going to the subroutine with these instructions in it I then had very fast ethernet comms. So am going to map all M0 accross in one instruction and all M1 in another instruction. Thanks again

iraiam said:

Are you sure your Ethernet port speed/duplex settings are all correct? The Ethernet port on the 5/05 and and the switchport should have the same duplex/speed settings. I just ran into this the other day. I was having trouble communicating reliably to a SLC. The port statistics in the switch showed a lot of MAC transmit/receive errors, FCS and CRC errors.

The symptom was very slow communications with RSlogix 500, and slow response on the HMI, The speed/duplex mismatch causes lost packets and bottlenecks the connection with re-transmitted packets of which a sizable percentage will fail again.

Click to expand...

Usually it's better to leave auto negotiation on all devices if possible. If you start using fixed on some devices, you might run into issues like that when a new device is connected or the setup is changed.

ruthbaker said:

I have a SLC 5/05 with really slow Ethernet comms. It is on a network with three Proface screens but comms is just as slow when I connect directly to the CPU. I have cleared bits S:2/15 and S:33/7 as suggested and this did improve the comms slightly but it is still very poor. I have tried different laptops, cables etc. Just wondered if anyone has experienced this before and how it was overcome?

Click to expand...

There is an error in the help files regarding these two System Bits. I think that it is S:33/7 that actually needs to be set, rather than cleared, to enable multiple messages to be processed.

I have one 64K SLC that is almost full. Used the SVC instruction about every 500 rungs and that speed it up quite a bit. But it also increased the scan time by about 50ms. But nothing it does requires high speed.