12bit DAC 测试实例

The dut is programmed using the ddd card with a three wire serial pattern. All ddd patterns are contained as functions in User.cpp. There are two

methods to program the device. The first method dynamically loads into ddd memory the required pattern based on the dac code desired. The

desired code is passed to the load_pattern() function and only the vectors required for that code are loaded into memory. This method allows the

user to easily load any of the 4096 possible patterns into ddd memory. The drawback to this is that it takes 1mS to run and can only be done from

within a test cycle thereby impacting test time. This method is used only during all codes testing in an engineering environment. The second

method is used for reduced code set testing. All patterns to test the designated reduced code set of this device are pre-loaded into ddd memory

when the test program is loaded. The function used is called pre_load_pattern(). The reduced code set is loaded as follows:

Codes 31 to 48

Codes 4079 to 4095

Codes 64 to 4080 (in steps of 32)

Codes 63 to 4079 (in steps of 32)

Code 0

Code 20

Code 50

In addition there is a pattern used for testing Data Out delay with a special synch bit (ddd chan 5) for capturing the rise and fall edges of Data Out.

The start and stop vectors for all of these codes are stored in memory. Special care should be exercised if any changes are to be made to this code.

Since these start and stop vectors are hard coded, changing any of the patterns will affect them causing improper device operation. If additional

codes need to be tested they should be added on to the end of the sequence so as not to affect the existing ones.