picboy

Cool So these PLCs allow direct acess to byte address ??? know i know some plcs allow byte addres S5 (semiens) old I know

Hi CX. Your right the focus is on the ladder, and most case it is better to be obvious in your programing tactics/structure rather than, optimised and compact considering most people that trouble shoot PLC's are more technical then programing savys. and might spend most of the time trying to figure out how are the program works My background Is a wide variety of programing VB Pascal C Keyence Omron AB Seimens Pic Basic(s) assembly Bla Bla.. So when I aprroach projects there is cross over practice applied but in the end when PLC programing my audience is the focus so I try and make my structure read fluent and obvious But I tend to get more compact and mindful of memory when programing in general! So I conseed to the statment "Why not byte access" But still feel that direct access to DM highbyte.lowwbyte would still be a desierable function. understanding that it can be done with some masking. or other methods

Yep your right! todays Processers have aloud for less focus on memory managment I come from and older methode of programming where it payed to be more atentive to your memory usage I do I lot of Pic Chip programming and you have to pay attention to to this or you run out! This discussion came up when we started to do serial port programming on the plc we thought this would be easier to just store our byte into a dm location and move just the byte it to the TXD function block well it moved the word not the byte this possed a small problem with the reciever and when we tryied to fix it we had to store the the byte in the lowbyte and waste the highbyte then store the next byte in the lowbyte of the secound DM2 and waste the highbyte pretty wasteful when have a few 1000 bytes to code We did figure it out with a stack,masks and pointers in the end More or less I was looking for some benifit but havent heard it yet! Moving words on a 16 bit bus is much faster and effcient notibly so, but that still no excuse in my expeerience to be ineffiecient with memory space Thanks Pic Boy

Hi Folks, So here is my question, It would seem that you can not access/declare byte access to DM location on more and more PLC's. For instance why not be able to access DM location like so {DM1.0 DM1.1} Assuming DM areas are words? rather than DM0,DM1, each a 16 bit word. It would seem a waste if I need to use a word for byte size data?? Is there any good reason for this? Omron PLCS CJ1 to specific RR