SIMCHECK II TIMING PARAMETERS SETUP

The SIMCHECK II test algorithm, in its default automatic test mode, has protection against errors due to tightly set timing parameters. While the settings are within specs, they may be somewhat laxed on certain modules. When you encounter questionable memory you may change these settings in order to test the memory under stricter conditions. SIMCHECK II'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 conditions for SDRAM modules can be accomplished by adjusting the speed settings via setup. To do so, enter the following sequence from Standby Mode:

Alternatively, you can also change the module's speed on the fly by pressing the F2 key during the Basic Test.

Please refer to our PC Communication Page for instructions on setting the Frequency Rate via Setup or via Change-on-the-Fly when using SIMCHECK II's PC Communication Program.

The following information is presented for those who wish to set stricter conditions on SIMCHECK II while testing EDO/FPM memory types.

SIMPLIFIED DRAM TIMING DIAGRAM

This is a simplified timing diagram showing 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

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. SIMCHECK 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. You will 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

Changing the Trah parameter is performed 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

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 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 device.

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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