SQL & PL/SQL

Hi Friends,
i have this table:

CREATE
  TABLE TB_GEN_COMPANY
  (
    "ID_COMPANY"   NUMBER NOT NULL ENABLE,
    "COD_CODIGO"    VARCHAR2(10 BYTE) NOT NULL ENABLE,
    "DES_NAME"    VARCHAR2(64 BYTE) NOT NULL ENABLE,
    "DES_DIRECTION" VARCHAR2(128 BYTE) NOT NULL ENABLE,
    "COD_RUC"       CHAR(11 BYTE) NOT NULL ENABLE,
    "FLG_EST"    CHAR(1 BYTE) NOT NULL ENABLE,
    "COD_USR_CR"  VARCHAR2(16 BYTE) NOT NULL ENABLE,
    "FCH_FEC_CR" TIMESTAMP (6) NOT NULL ENABLE,
    "COD_USR_MOD" VARCHAR2(16 BYTE) NOT NULL ENABLE,
    "FCH_FEC_MOD" TIMESTAMP (6) NOT NULL ENABLE,
    CONSTRAINT "TB_GEN_COMPANIA_ESTADO_CHK" CHECK (FLG_ESTADO IN ('A', 'I'))
    CONSTRAINT "TB_GEN_COMPANIA_PK" PRIMARY KEY ("ID_COMPANIA")
  )

I want to validate the code (cod_codigo). if the record exists, i will have to update with the news inputs parameters, otherwise it should create a new one i mean, an Insert.

Thanks for t he help.

Sorry for bad engl.