l~) Main Ram Content Test - This test verifies the main memory contents, using two data patterns (Number ~~~~ and Number ffff ) to check for a short-circuit to ground or +5 Volt. The following algorithm is used in this memory test: A) Write a data pattern of 5555(hex) to the first location of a segment, then read back the data pattern. If the data read back is 5555(hex), the segment is valid. The entire segment (64K bytes) is then tested with two data patterns (Number ~~~~ and Number ffff). If the data read back is ffff(hex), the entire segment is not there. The test then checks to see if the missing segment is within the basic memory range (segment ~ to 3).
If so, an error exists since there can not be a gap within the basic memory range. If the missing segment is outside the basic memory range, the test continues on. If the data read back is anything other than 5555(hex) or ffff(hex), there are bad bits in this segments. B) Increment the segment counter and check it in the following ways: If it is less than segment 7, go to step A. If it is larger than segment D, the memory test is completed. If it is equal to segment 8, the test checks the wrap- around by writing the first location of segment 8 with a pattern of aaaa(hex) and checks the first location on segment ~.
If the first location of segment ~ is aaaa(hex), a wrap-around occur ed, and the test is completed. If the first location remains as 5555(hex), the Monitor returns to step A and continues on to test segments 8 to F (up to the Monitor's area). 11) Interrupt Controller (8259) Test - Two data patterns (Number ~~~~ and Number ffff) are used in a static test to write and read to the system interrupt controller (8259). These two patterns detect possible short-circuit with ground and + 5 Volt. 6-21