Non-volatile memory is essential for storing critical data. It allows for persistent configurations and direct data access of the persistent without having to rely on external media. These advantages come with the Human-Machine Interface (HMI), meaning any external media does not have to be cared for or warrantied.
Every Monitouch HMI comes with more than a hundred kilobytes of Static Random Access Memory (SRAM), whose data is maintained by a coin cell battery in the rear of the HMI. This area is used for Logging and Alarms, but the programmer can also use it for saving everything from recipes to machine configurations. In this blog, we will cover how to assign SRAM to be used as an internal memory device and a simple use case with a Macro.
To make use of SRAM, one must first enable it. To do so, open Smart Editor, go to System Settings, and click on SRAM as shown in the snippet below.
For V-Sft Users, locate System Settings, click on Unit Setting, and select SRAM/Clock.
Both Configuration Software Suites use the same settings shown below.
The SRAM Auto Format option will format the SRAM every time the application is downloaded. Useful for development as a mismatched format will error out the HMI. However, we recommend turning this off for deployment as any future download of the application will delete all SRAM data.
For reference, Memo Pad is used for leaving written notes, but that is beyond the scope of this article. If you have further questions on how best to use Memo Pad for this purpose, please feel free to reach out to the Live Automation team anytime. Our team is always here to help.
The next two settings, $L and $LD, are the main focus of this article. Using this window, you can assign different amounts of non-volatile memory to single-word or double-word amounts. The more you assign, the more battery will be used, so it is best practice to ship the exact amount you require to minimize maintenance on your machine. However, the lifespan is still measured in years even when in full use.
$L and $LD addresses can be used in nearly every place a $u address can be used, meaning it is just a matter of changing the address space to make your code and data survive power cycles.
As an example of persistent data, here is an example of an initial macro:
IF($L00000 == 0) (W)
$L00000 = 14 (W)
$L00001 = 51 (W)
$L00002 = 6230 (W)
$L00003 = 2AF9H (W)
$L00004 = 35 (W)
$L00005 = 123 (W)
;
ENDIF
In this macro, we check if an address is zero; if so, we assume data loss and load the default parameters. If these parameters are changed, then it is saved in SRAM and retained between power cycles by the coin cell battery. This allows for end-user or startup configuration without having to modify the entire application in the field.
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Want to watch this process on video? Check it out on YouTube: Monitouch V-Series HMI Non-Volatile Memory: Assigning SRAM
