Ken Roach
Lifetime Supporting Member + Moderator
I have a customer who is trying to use Allen-Bradley PowerFlex 70 drives with a Profibus interface with an SST Profibus scanner for the PLC-5 controller.
If you're familiar with A-B drives and the way they work on networks, they generally map two 16-bit Words of Input and Output data each.
The first 16-bit Word of Input is bitwise status; drive enabled, running, etc. The second 16-bit Word of Input is a value that feeds back the Output Frequency.
The same is true for Output data, except the Command word represents Stop, Start, Jog, etc. and the Frequency Reference is the frequency at which the drive will run.
What's working strangely in this configuration is that the two bytes that make up each 16-bit Word for the drive appear to be swapped when they end up in the PLC-5 data table.
What I've gotten from SST and A-B technical support is that the SST module will map Word data differently from Byte data; if your GSD file defines a data object as Word type, it will be mapped High byte first. If it defines the data object as Byte type, it will be mapped Low byte first. That's all they had to say, so far.
So how do I change my GSD file ? The only place I can imagine the format of the I/O Module is defined is in a string of octets in the Module configuration section:
Module = "Ctrl/Stat & Ref/Fdbk (2+2bytes)" 0xC1, 0x83, 0x83, 0x01;
EndModule;
Does anyone know what those four hex bytes mean in a GSD file ?
I have searched all over various Profibus trade organization sites and even downloaded their GSD Editor, but only want to solve this one little conflict, not develop a Profibus product or join the PTO, and thus don't want to pay 300 GBP for the Specification.
If you're familiar with A-B drives and the way they work on networks, they generally map two 16-bit Words of Input and Output data each.
The first 16-bit Word of Input is bitwise status; drive enabled, running, etc. The second 16-bit Word of Input is a value that feeds back the Output Frequency.
The same is true for Output data, except the Command word represents Stop, Start, Jog, etc. and the Frequency Reference is the frequency at which the drive will run.
What's working strangely in this configuration is that the two bytes that make up each 16-bit Word for the drive appear to be swapped when they end up in the PLC-5 data table.
What I've gotten from SST and A-B technical support is that the SST module will map Word data differently from Byte data; if your GSD file defines a data object as Word type, it will be mapped High byte first. If it defines the data object as Byte type, it will be mapped Low byte first. That's all they had to say, so far.
So how do I change my GSD file ? The only place I can imagine the format of the I/O Module is defined is in a string of octets in the Module configuration section:
Module = "Ctrl/Stat & Ref/Fdbk (2+2bytes)" 0xC1, 0x83, 0x83, 0x01;
EndModule;
Does anyone know what those four hex bytes mean in a GSD file ?
I have searched all over various Profibus trade organization sites and even downloaded their GSD Editor, but only want to solve this one little conflict, not develop a Profibus product or join the PTO, and thus don't want to pay 300 GBP for the Specification.