AMM says:
... Abort Mode (AB) The purpose of the abort mode is to prevent the cabin climbing if the aircraft does not climb after take-off. (For example, if an engine failure happens after V1 the aircraft must take-off). The system will switch to the climb mode after take-off. If the aircraft descends, instead of climbing, while the altitude is below 8000 ft. or below 5000 ft. above take off field the system switches into the abort mode. The cabin pressure is then kept to the value before take-off.
