The 8000 was a handheld model, no DB-25 involved. The programming sequence varies depending on your keypad. The 6-digit security code is factory set to "000000", though it can be changed in the programming as well.

If you have a FCN & RCL key, then it's "FCN, 0, (6-digit security code twice), RCL". This will do most models.

Some very old models dropped the first "0", to make it "FCN, (6-digit security code twice), RCL".

If you have a FCN & MEM key, then it's "FCN, 0, (6-digit security code twice), MEM".

If you have no FCN key, but have a STO key, then try "STO, #, (6-digit security code twice), RCL".

If you have a CTL & RCL key, try "CTL, 0, (6-digit security code twice), RCL".

If you have a CTL, but no RCL key, try "CTL, 0, (6-digit security code twice), *".

Unlock code is step 8 in the programming. Step through with the "*" key, hit SND at any step display screen to save & reboot the phone.

If these don't work, the security code has likely been changed. Often times people will either put in 123456, or the lock code twice. Since you don't know the lock code, that won't help you. In that case, you need to put the phone in test mode. Looking at the back of the phone with the battery off, you should see a set of 12 gold pins at the top. The top right pin needs to be grounded upon power-up to put the phone in test mode. The display should flash numbers on it. Hit "#", 55, "#" to enter programming. Once again, "*" steps you through, the lock code is still step 8. In this mode, you must step all the way through until a small apostrophe appears in the display & the "*" button won't scroll any further. Then hit SND to save.