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Guest NiMot03

Memory size and Program Size

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This is my first PLC project, I come form the MicroSoft-centric world. I am assisting my client with their hardware selection. Without having written the program, how do I know what size my final program will be. They have an existing similar program that is 1 ladder with 130 rungs. Mine will have at least two ladders with a total of at least 200+ rungs. So, how can I estimate the memory requirement for the program and recommend an appropriate processor (in the SCL 500 series)? We are also looking at using two 1746-HSTP1 Stepper Control Modules and a 1747-DTAM-E Data Table Access Module. Do they require any memory overhead from the processor? Any help pointing me in the right direction will be greatly appreciated. Nick

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You can get manuals from AB's web-site detailing the amount of memory used and execution times for individual instructions. Usually, a more significant factor is data storage. Note that instructions such as timers and counters use 3 words of data memory in addition to whatever they use in program memory. There are other things to consider and I would recommend against a minimalist approach. Note that the bottom of the SLC range 5/01 and 5/02 do not support on-line programming. This can significantly increase commissioning time, since you have to shut down whatever you're controlling every time you want to make a change. Also, if you have a DTAM connected to one of these, you can't connect your programming terminal, unless you add networking hardware (AIC, etc.). The DTAM itself is very limited in what it can do. Do yourself and your client a favour. Select a model that supports on-line programming and supports a network, and forget any of the DTAM devices in favour of a PV300 or 600. My choice would be a 5/04 and put the PV and programming on DH+. You'll be able to work better and be able to add all the extra features that your client hasn't mentioned or thought of yet. You will also have plenty of memory. Edited by Gerry

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My general rule of thumb is for 503 and 504 is 16k memory for anything less than 250 rungs, like Gerry said it gives you plenty of breathing room for later additions. I have went with a 8K 503 processor before and the client starting wanting additions to his PanelView that soon caused memory problems and forced us to upgrade to a 16K module.

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I once read in a manual that you can anticipate the memory size of the program based on the size of the IO. Just multiply the number of inputs/outputs by 10 and then you have a rough estimate of the size of the program, so if you have 200 inputs and outputs you'll need 2K of memory. But this is just a simplistic aproach.

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