Changing Timing Parameters on the RAMCHECK for SDRAM Modules

INN-8668-APN18
--Created 5-10-2005

The RAMCHECK test algorithm, in its default automatic test mode, has protection against errors due to tightly set timing parameters. While the settings are within specifications, they may be somewhat relaxed for certain modules. When you encounter questionable memory you may adjust these settings in order to test the memory under stricter conditions. RAMCHECK's ability to change timing parameters sets it far ahead of the competition! Changing timing parameters is easy and can be done by all advanced users. This application note guides you further when you want to adjust any of these settings.

SDRAM SETTINGS

Setting tighter test conditions for SDRAM devices can be accomplished by manually selecting the frequency which will disable the default automatic mode. There are two ways to do this, The easiest way is by the "Change-on-the-Fly" method which changes the test frequency only on the current SDRAM device that you are testing. Insert a SDRAM device and press the "F1" key like you would normally do to start the Basic Test, noting the frequency that the automatic mode detected. At any time during the Basic Test press the "F2" key. A menu will be displayed. Press "F1" for Speed (Frequency), which should automatically display the frequency detected in Auto Mode. If not, use the "F2" and/or "F5" keys to select the frequency you noted earlier. Now press "F1" to start the test. This will disable the default automatic mode and test the module at the selected frequency even through the Extensive and Auto Loop test phases.

The second way to manually change the test frequency is via the RAMCHECK Setup. This is useful if you want to test several SDRAM devices at a selected frequency. You can enter the Setup menu by pressing "F2" while you are in standby mode, then press "F1" for "SETUP PARAMETERS". Next press "F1" for "TIMING", then "F1" for "SPEED", then "F1" for "SETUP FREQUENCY". Use the "F2" and/or "F5" keys to select the desired frequency and then press "F1" to enter it. Next press the "ESC" key a few times to save it. You should see "SAVING to EPROM" displayed on the LCD before the RAMCHECK resets. This change will remain in the RAMCHECK's internal memory even if you turn the unit off then on again. Once you finish your test you can reset the RAMCHECK back to its default automatic mode by simply pressing the "F2" then "F4" keys while you are in standby mode.

You can also use the RAMCHECK's "SETUP" or the "Change on the fly Method" to adjust the frequency slightly faster to check the quality and overclocking capabilities of the SDRAM device.

FPM/EDO SETTINGS

This section provides information for those who wish to set stricter test conditions on the RAMCHECK while testing older EDO/FPM memory types.

SIMPLIFIED DRAM TIMING DIAGRAM

This is a simplified timing diagram that shows a single read operation. The 'X' shape on the address signal indicates a switch between the row address and the column address, which are multiplexed on the address lines.

Trah is the address hold time; it is the time that the row address needs to be held after the activation of the RAS signal.

Trcd is the RAS to CAS delay time; it is the time interval after RAS activation when CAS is activated. At this time, the address lines need to have a stable column address.

Data from the DRAM is available at the Trac, after RAS activation, and is the main access time of the DRAM device.

LOADING AFFECT ON DRAM OPERATION

When several modules are put into a motherboard, they cause a higher capacitive load on the control, address, and data lines; thus the system is likely to encounter data errors. These data errors will then disappear when using fewer modules. Figure A above shows low loading affect as you expect to find in a normal system. Figure B shows what happens to the each of the timing signals as a high load occurs. The shaded area shows an unstable state, which can cause memory errors as a result of heavy loading.

Setting Trcd, the RAS to CAS Delay Time on EDO/FPM Modules

Changing the Trcd parameter is performed by first entering the following key sequence from Standby Mode:

Entering this sequence allows you to set a new value, or to return to the automatic default value of 24nS. If you choose to setup a new value, the screen will change to display a graphic representation of the RAS signal, the Address signal, and the CAS signal, and how they compare to each other. RAMCHECK provides this graphic display as follows:

The parameter in question is the relation of the CAS signal to the RAS signal. After you have selected the new value, press F1. The value is changed by pressing the or keys. Please note that the CAS signal will move along with your changing value. Increasing this parameter will give a broader test, while decreasing it will provide a tighter setting. An adequate setting would be reducing it to 21nS for a stricter test.

Setting the Trah, the Row Address Hold Time for EDO/FPM

Change the Trah parameter by first entering the following key sequence from Standby Mode:

As with the Trcd setting, you will be prompted with two choices: the setup of a new value, or auto, which returns to the default setting of 11nS. Choosing to setup a new value will yield the following screen. The parameter in question is the relation of the Address signal to the RAS signal. After you have selected the new value, press F1.

The value is changed by pressing the or keys. You will note that the Address signal will move along with your changing value. An adequate value should be one that places the Address signal within the window that lies between the RAS signal and the CAS signal. When testing for load sensitivity, we recommend a Trah value of 12nS, while the Trcd is set to 21nS.

Setting DUT Refresh

Changing the Refresh parameter for the Device Under Test (DUT) is performed by first entering the following key sequence from Standby Mode:

The Refresh value can be set to AUTO, NONE, or a fixed interval of 2mS-999mS by using the or keys. After you have selected the new value, press F1.

The longer the interval is set, the slower the refresh rate will be. Memory devices sustaining data at longer refresh intervals (higher set values) are typically of higher quality. Entering a larger value than the default, or even setting this parameter to NONE will provide stricter guidelines for the DUT. Setting a value to NONE will insure that the only refresh present is that from the test scan of the memory rows (dynamic refresh).

Setting DUT Speed, Trac for EDO/FPM

Changing the Speed parameter is performed by first entering the following key sequence from Standby Mode:

This function will allow you to change the access time from RAS using the or keys. For a stricter test, setup your speed to be slightly faster than the rating of your module.

After you have selected the new value, press F1. The following screen will appear.

Select TEST DUT AT SETUP SPEED and then press F1. This will eliminate repeated tests and detect more intermittent faults in the memory. It also allows you to find the slower chips on your memory module.

Although all of the above parameter changes may not be necessary for your particular application, we do encourage that you experiment with these setup modes to find which setup best suits your individual needs.

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