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J-Mem main window

J-Mem memory viewer is a GUI application to display and modify the RAM and SFRs (Special Function Registers) of target systems while the target is running. J-Mem is part of the J-Link Software and Documentation Pack, which is available for download on the SEGGER webpage.

Setting up J-Mem

When starting J-Mem a configuration dialog pops up, letting you select the needed configurations to connect to J-Link and the target.

J-Mem: Configuration

Note: To make sure the connection to the target device can be established correctly, the device, as well as the interface and interface speed have to be given on start of J-Mem.

J-Mem user interface

The user interface of J-Mem shows the content of a memory region from the target that J-Link is connected to. Furthermore, details about the connection to the target are displayed in the status bar.

The memory window provides a range of different options regarding the displayed memory.

J-Mem: Memory window options

In the following, these options are explained in detail from left to right (as seen in the screenshot above).

Go To

Using the Go To field (JMem IconGoTo.PNG), the first address shown in the memory window can be set. The button to the right of the edit-field returns to the previously selected address.

Access width

Using the red buttons (JMem IconAccessWidth.PNG) to the right of the "Go To" field, the access width can be set. The number inside each button refers to the number of bytes that are accessed at once. This means that:

  • 1 refers to 8-bit access,
  • 2 refers to 16-bit access and
  • 4 refers to 32-bit access.

Fill memory

By clicking the icon (JMem IconFillMem.PNG) next to the access width buttons, a range of memory can be filled with a custom value.

J-Mem: Fill memory

A custom <Fill Value> can be chosen that the selected memory region is filled with. The region to fill can be determined by setting the <Start Address> and either the <End Address> or <Size>.

Save memory data

The button (JMem IconSaveMem.PNG) to the right of the "Fill memory" icon makes it possible to save a memory range in a binary file.

J-Mem: Save memory data

Similar to the "Fill memory" option, the memory region to be saved can be determined by setting the <Start Address> and either the <End Address> or <Size>.

Periodic Refresh

By default, J-Mem only reads the memory to be displayed once when it is shown for the first time. Using the "Periodic Refresh" option, a time interval for the refresh rate of the displayed data can be set.

J-Mem: Periodic Refresh

One of the following intervals can be selected:

  • 100 ms
  • 200 ms
  • 500 ms
  • 1 s
  • 2 s
  • 5 s
  • off

The time interval "off" is the default and does not refresh the displayed memory periodically.

Command line options

There are no command line options available for J-Mem.