Translation:Shulchan Aruch/Orach Chaim/284
1. The Laws Pertaining to the Haftarah and Its Blessings, 7 Seifim: We conclude in the Prophets based upon the subject of the parashah, and we do not decrease [the length of the haftarah] from 21 verses other than if the matter is settled in less than that, for example, “add your burnt offerings to your sacrifices” [in Jeremiah 7:21]. RAMA: And only on Shabbat on the matter of 21 verses: three verses for each one of the [seven Torah] readings, but on a Festival on which five read [the Torah], fifteen verses suffice (Maharam). And it was decreed that the haftarah is only [read] in public after they read the Torah (Ramban’s Responsa, Siman 199), but nevertheless it is forbidden to read with the blessings before it and after it; but with no blessing it is permitted (Beit Yosef).
2. If Rosh Chodesh falls on Shabbat, the maftir does not mention Rosh Chodesh at all (note: in the blessing Al haTorah). There are those who say that even though we do not mention Rosh Chodesh at the end, we remember it (mention it) within the blessing, where we say 'את יום המנוח הזה ואת יום ראש החודש הזה'. The custom is like the first opinion.
3. One must concentrate on listening to the blessings recited by those reading from the Torah and the blessings of the maftir, and respond Amen to them. [This will benefit the one who responds, since his responses] enable him to reach the required sum of 100 blessings [to be recited daily]. (On Shabbos, he is lacking the required number of blessings,29 and responding Amen to these blessings can compensate for that lack).
4. A minor may recite the haftarah. RAMA: If one who did not know how to do the haftarah was called to the maftir aliyah, another person can say the haftarah. However, initially it is forbidden to do this.
5. If the maftir lost his ability to speak in the middle of the Haftarah, the person who comes to replace him and complete [the reading] should not begin from the place where [the reader] ceased. Instead, he should begin from the place where the first began, as is done with the Torah reading. RAMA: Two people may not say the haftarah at the same time, because (of the principle) 'two people should not use the same keli'. (Rivash)
6. The maftir may not begin the haftarah until the golel (the one who wraps the Torah scroll) finishes wrapping the Torah.
7. On a Shabbat where the parshas are joined we recite the haftarah for the second parshah. RAMA: And see later Siman 428. It is our custom to remember the names of the departed after the reading of the Torah and to make the blessing 'העוסקים בצרכי צבור' (who is involved in the needs of the congregation), every place according to its custom (Shibuleit Haleket; Hagahos Mordechai). We are accustomed to saying 'Yekum Purkan' and this is not a violation of making a plea on Shabbat. We are also accustomed to saying 'Av Harachaman' and on every day where we do not say 'צדקתך צדק' we do not say 'Av Harachaman', except only when we bless the New Month during the counting of the Omer. And everyone should follow his custom regarding this.