This article has been copied from a Dr. Dobb's Journal issue, originally found here. The original article can also be found here
The code in this article has been used to create a banked RAM tester for the commander x16 that can be found at https://github.com/JimmyDansbo/ramtest/
A HIGH-SPEED MEMORY TEST PROGRAM FOR THE 6502
by Jim F. Butterfield
14 Brooklyn Avenue
Canada M4M 2X5
Received: July 1, 1977
A recent algorithm by Knaizuk and Hartmann (IEEE Transactions on Computers, April 1977) outlines an ultra-fast RAM test.
The program below is based on this algorithm, but sacrifices testing efficiency to a small degree so as to achieve program compactness and simplicity. The test will detect any single stuck-at-1 or stuck-at-0 fault in a RAM, including the memory itself, the address and data lines, and the address decoders. Its run time is dramatically short compared to most memory test programs. The speed advantage becomes more pronounced as the amount of memory tested increases.
Each 'pass' of the test follows the following pattern:
It is important to note that the above three steps must be done as three separate iterations. The above pass is performed three times, with the position of the 00 value changed each time. Then the whole thing is repeated, exchanging the FF and the 00 values.
the program given here is written for the KIM system; the indirect address pointer is positioned so that KIM will display it upon termination. For other systems, the pointer may be relocated and output as convenient. Subroutines and stack operations have been carefully avoided to allow the test to include page 1 of memory if desired. Memory is tested as a group of 'pages' rather than between any two arbitrary addresses; this is not essential but is usually convenient and helps the speed.
Address of the first and last pages to be tested should be placed in locations 0000 and 0001 respectively. The program starts at address 0002; it will halt showing a memory address on the display. This will be either the address of a fault, or (highest location tested + 1) for no fault.
MEMORY TEST June, 1977 Jim Butterfield, 14 Brooklyn Ave., Toronto, Ontario Canada M4M 2X5 0000 xx BEGIN xx starting page for memory test 0001 xx END xx ending page for memory test 0002 A9 00 START LDA #0 zero pointers.. 0004 A8 TAY into low-order 0005 85 FA STA POINTL addresses 0007 85 70 BIGLP STA FLAG =00 first time, =FF second 0009 A2 02 LDX #2 000B 86 72 STX MOD 3 tests in each major loop 000D A5 00 PASS LDA BEGIN set pointer to.. 000F 85 FB STA POINTH ..start of test area 0011 A6 01 LDX END 0013 A5 70 LDA FLAG 0015 49 FF EOR #$FF reverse FLAG 0017 85 71 STA FLIP =FF first time, =00 second 0019 91 FA CLEAR STA (POINTL),Y write above value.. 001B C8 INY ..into all locations 001C D0 FB BNE CLEAR 001E E6 FB INC POINTH 0020 E4 FB CPX POINTH 0022 B0 F5 BCS CLEAR ; FLIP in all locations; now change 1 in 3 0024 A6 72 LDX MOD 0026 A5 00 LDA BEGIN set pointer.. 0028 85 FB STA POINTH ..back to start 002A A5 70 FILL LDA FLAG change value 002C CA TOP DEX 002D 10 04 BPL SKIP skip 2 out of 3 002F A2 02 LDX #2 restore 3-counter 0031 91 FA STA (POINTL),Y change 1 out of 3 0033 C8 SKIP INY 0034 D0 F6 BNE TOP 0036 E6 FB INC POINTH new page 0038 A5 01 LDA END 003A C5 FB CMP POINTH end of test area? 003C B0 EC BCS FILL no. keep going ; memory set up - now test it. 003E A5 00 LDA BEGIN set pointer.. 0040 85 FB STA POINTH ..back to start 0042 A6 72 LDX MOD synchronize 3-counter 0044 A5 71 POP LDA FLIP test for FLIP value.. 0046 CA DEX ..2 out of 3 times 0047 10 04 BPL SLIP - else - 0049 A2 02 LDX #2 reset 3-counter 004B A5 70 LDA FLAG & test for FLAG value 004D D1 FA SLIP CMP (POINTL),Y make the test 004F D0 15 BNE OUT branch if failed 0051 C8 INY 0052 D0 F0 BNE POP 0054 E6 FB INC POINTH 0056 A5 01 LDA END 0058 C6 FB CMP POINTH 005A B0 E8 BCS POP ; above test OK - change & repeat 005C C6 72 DEC MOD change 1 in 3 position 005E 10 AD BPL PASS .. & do next third 0060 A5 70 LDA FLAG invert flag.. 0062 49 FF EOR #$FF ..for part 2 0064 30 A1 BMI BIGLP 0066 84 FA OUT STY POINTL low order adds to display 0068 4C 4F 1C JMP START ..and exit to KIM 006B end