Digital Test Patterns
Test Patterns
There are a numbers of ways to check for design or build issues with a
data bus.
Send a pattern of alternating 0x5's and 0xA's; over the data
bus.
Checks for bits stuck high or low [0101, followed by
1010]
Send a pattern of 0x0 and 0xF;. over the data bus.
Checks for bits stuck high or low [0000, followed by
1111]
Checks for ground bounce issues with the input of the
driver
Send a pattern of 0x0 and 0xE;. over the data bus.
Checks for ground bounce issues with the output of the driver
[0000, followed by 1110]
A four bit data bus is shown, but it's the same regardless of the bus
width. Just keep the pattern true for the width of the driver chip. The
exception is the 0xE, if the driver IC is 8-bits wide send 0xFE, not
0xEE.
In fact when using a 16 bit bus you could treat each 8 bit wide bus as a separate bus. Some chips have 8 bit interfaces while other chips have 16 bit interfaces. If 8-bit wide ICs are used, consider the two ICs as individual to determine if one IC is mis-connected to the other. That is, send one digital pattern through the lower 8 bits while sending a different pattern through the upper 8 bits.
This may sound like common sense, but you would be surprised. When testing use a test pattern that will test any and all possible conditions. Just pushing through all FFs will only show that the devices have power and are maybe connected, but a bit that is stuck high will never be found.
Related Test Topics
Digital Logic Pitfalls, or Design for Test, or IC Test Circuits.
