Throughout the game you will find passcodes. Some of these are story related and can't miss. Some you can miss if you don't return to previous sections and kill the porters in the area. Below I will list all 14 of the passcodes and what they are for.
1. pass_global - Allows Jehuty to leave area's this is story related and can't miss it.
2. pass_javelin - Allows Jehuty to use the sub weapon "Javelin". This can be found in town.1 after you fight Tempest.
3. pass_phalanx - Allows Jehuty access to use the sub weapon "Phalanx". This can be obtained in the second rescue mission.
4. pass_antilia - Gives information about Antilia. This is obtained through factory 1. This is story related and can't be missed.
5. pass_geyser - Gives Jehuty access to use the sub weapon "Geyser". This is found in City.1 after killing the squad leader.
6. pass_halberd - Gives Jehuty access to use the sub weapon "Halberd". This is found in eps.1 after killing all the porters.
7. pass_control1 - Required for the story to proceed and control the raptor. This is found in EPS.2 after killing the upgraded enemies.
8. pass_control2 - Required for the story to proceed and contol the raptor. This is found in Town.1 after killing the squad that has passcode in the name.
9. pass_vaccine - Story related, can't miss. This is found in Factory.2.
10. pass_decoy1 - Story related and required to kill a boss. This can be found in City.2 after killing a squad.
11. pass_decoy2 - Story related and required to kill a boss. This can be found in Town.3
12. pass_comet - Allows Jehuty to access the sub weapon "Comet". This can be found in City.2 after destroying the porters.
13. pass_gauntlet - Allows Jehuty to access the sub weapon "Gauntlet". This can be found in ESP.2 after destroying the porters.
14. pass_bounder - Allows Jehuty to access the sub weapon "Bounder". This can be found in Mountain.1 and taking the left at the beggining.
Achievement will pop after picking up the last one.