5.1.2000 News from the LGP-30
("No. 4 lives")

One of the first test programs that run on the LGP-30 and did something useful was:

  3w00  b2700	/ bring contents of word 2700 (track 39) into accumulator
  3w04  z8000	/ conditional halt
  3w08  b3w00	/ bring contents of word 3w00 into accumulator
  3w0j	a3w80	/ add contents of word 3w80 to accumulator
  3w0w  c3w00	/ store accumulator into 3w00 and clear
		/ (tribute to J. v. Neumann)
  3w10  u3w00	/ jump unconditionally to 3w00

  3w80  00004	/ constant used to increment the address

With the help of this loop it was possible to check that the program fragments on tracks 39 to 42 that we had read out earlier with the logic analyser were also correctly read by the LGP-30.

Unfortunately the game was quickly over. At the next session we found out that two instruction didn't work: The Y instruction (address replacement) and R instruction (store return address). Both instructions are related. They modify the address part of the word addressed by the instruction. When the computer ran normally these instructions just didn't do anything. When executing with "EXECUTE INSTRUCTION" they replaced the address part of all 64 words of a track.

Finding this fault would be more work than the bad contact in the tube socket.