标题: 12bit DAC 测试实例-说明较详细，值得参考！ [打印本页] 作者: admin 时间: 2008-9-28 11:25 标题: 12bit DAC 测试实例-说明较详细，值得参考！ 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.