MB+ Communication question


Thread Starter


Using Read_Reg function block to read register data from device over MB+. Although a large number of READREG function blocks can be programmed, only four read operations may be active at the same time. HOW CAN I USE MORE THAN FOUR Read_Reg function block IN MY PROGRAM? Thanks!
A PLC only has 4 data master paths. That is why you can only have 4 functions active at a time. If you need more, then you must add a 2nd MB+ adapter to your controller. To use the 2nd adapter, set the high byte in the first routing register to 1 and the low byte to the actual routing address.

Lynn at Alist

MB+ allows only 4 active 'connections' at one time. The instant you activate a 5th, you start "thrashing" connections which means the MB+ network as to continuously open/close all 5 as it cycles thru them. This will slow your network for every node.

I should first make sure remote nodes "pack" the data you want into one area so you only need 1 read per remote.

If you must run more than 4, use ladder logic - timers or the completeion of 1 block to activate the next.
You have to multiplex them. fire off one, then when it is finished, shut it down and fire off the next one. Continue until you hit them all, then start over at the top.

Actually, if you have more than 4 MSTRs in your program and enable ALL of them ALL of the time, then over time, they will ALL be serviced the same. Or, you can use the MSTR function (or MBP_MSTR) to sequence functions. Start one and when it is done, start the next. The MSTR function is preferred by many because it is the only one of the many functions that you can "control".