MEMORY PLUS Manual By Lee Davison and Hans Otten Back to The Computerist

				    RAM Memory Test

	You should test the MEMORY PLUS RAM when you initially set up your system.
	You may also want to test it from time-to-time to make sure it is all still
	working properly.  And, of course, you will want to test it whenever you have
	any reason to suspect that it may not be working right.  The following memory
	test is based on the work cited under "NOTES" on page 24.

	"Testing RAM isn't just a question or storing a value and then checking it.  It's
	important to test for interference between locations.  Such tests often involve
	writing to one location and then checking all other locations to see they haven't
	been disturbed; this can be time consuming.

	This program checks memory thoroughly and runs exceptionally fast.  It is adapted
	from an algorithm by Knaizuk and Hartmann published in "IEEE Transactions on
	Computers", April 1977.

	The program first puts value FF in every location under test.  Then it puts 00
	in every third location, after which it tests all locations for correctness.
	The test is repeated twice more with the positions of the 00's changed each
	time.  Finally, the whole thing is repeated with the FF and 00 values inter-
	changed.

	To Run:  Set the addresses of the first and last memory pages you wish to test
	into locations 0000 and 0001 respectively.  Start the program at address 0002;
	it will halt with a memory address on the display.  If no faults were found,
	the address will be one location past the last address tested.  If a fault is
	found, its address will be displayed."

	The MEMORY PLUS version of the memory test is set up to test from page 20
	(2000 hex) through page 3F (3FFF hex).  After loading the program from the
	cassette tape (or by hand), set address 0002 and press GO.  If the memory
	checks out completely, then after a few seconds the display will show the
	address 4000 in the address portion of the display.  If an error is detected,
	then the address containing the error will be displayed.  Since the program
	will halt at the first detected error, there is no way to test for additional
	errors within a page beyond the first error.  You can test other pages by
	changing the starting and ending page addresses in locations 0000 and 0001.
	The program may be re-run any number of times by restarting it at location
	0002.



	Once a bad location has been detected, you can examine the location via the
	MICRO Monitor and perhaps determine the problem. For example, if the location
	has a data value of 7F, it would indicate that the most significant bit was
	not working.  Refering to the Memory organization drawing you could determine
	which 2102 chip was responsible for this bit.  Since the RAM chips are all
	socketted, it is a simple matter to remove the suspect chip and replace it
	with another chip.  Even if you do not have any spare 2102 chips handy, you
	can swap the suspect chip with another chip and see if the problem moves with
	the chip or stays in the same location.  IMPORTANT NOTE:  Turn the power off
	when removing any chips, otherwise you may destroy the memory chips.  If the
	problem moves with the chip, then the solution is to get a replacement chip.
	If the problem does not move with the chip, then you must look elsewhere for
	the solution.

	The next test would be to swap the 74LS367 chips and see if the problem shifted.
	Then the 74LS138 chips could be swapped.  Finally you could replace the 74LS00,
	74LS32, or 74LS04 chips.  Note that the replacements do not have to be "LS" type.
	One of the above chip replacements should solve 99% of the problems which occur
	in the field.