Siman 236
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א בָּעֶרֶב מְבָרֵךְ שְׁתַּיִם לִפְנֵי קְרִיאַת שְׁמַע, וּשְׁתַּיִם לְאַחֲרֶיהָ.
1 In the evening, we make two blessings before the recitation of Shema, and two after it.
ב אֵין לְסַפֵּר בֵּין גְּאֻלָּה דְּעַרְבִית לַתְּפִלָּה, וְאַף הַנּוֹהֲגִין לוֹמַר י"ח פְּסוּקִים וְיִרְאוּ עֵינֵינוּ, אֵין לְהַפְסִיק בֵּין יִרְאוּ עֵינֵינוּ לַתְּפִלָּה; וּמִיהוּ מַה שֶּׁמַּכְרִיז שְׁלִיחַ צִבּוּר רֹאשׁ חֹדֶשׁ בֵּין קַדִּישׁ לִתְפִלַּת עַרְבִית לָא הָוֵי הֶפְסֵק, כֵּיוָן שֶׁהוּא צֹרֶךְ הַתְּפִלָּה; וְכֵן יָכוֹל לוֹמַר: בָּרְכוּ, לְהוֹצִיא מִי שֶׁלֹּא שָׁמַע, וְלָא הָוֵי הֶפְסֵק. הַגָּה: וְעַיֵּן לְעֵיל סִימָן ס"ט. רָאִיתִי מְדַקְדְּקִים נָהֲגוּ לַעֲמֹד כְּשֶׁאוֹמְרִים הַי"ח פְּסוּקִים שֶׁל בָּרוּךְ ה' לְעוֹלָם וְכו' (תְּהִלִּים פט, נג) וּמִנְהָג יָפֶה הוּא כִּי נִתְקְנוּ בִּמְקוֹם תְּפִלַּת י"ח, וְעַל כֵּן רָאוּי לַעֲמֹד בָּהֶן כְּמוֹ בַּתְּפִלָּה.
2 One should not talk between the blessing about redemption (ge'ulah) in the evening and the Amidah; even those who routinely say 18 verses and "yir'u eineinu" should not pause between that paragraph and the Amidah. What about when the reader announces Rosh Chodesh [so people can remember to say ya'aleh ve'yavo] between Kaddish and the evening Amidah? This is not a pause, since it is a requirement for the Amidah; and thus, one could also say that Barekhu, to exempt one who did not hear it, wouldn't be considered a pause either. Rema: "See above in section 69. I have seen sticklers who stand while saying the 18 verses of "barukh adonai le'olam" etc. (Ps. 89:53). This is a nice custom because it was set in place of the 18 blessings [of the Amidah], and thus one should stand for them like they do for the Amidah."
ג מָצָא צִבּוּר שֶׁקָּרְאוּ קְרִיאַת שְׁמַע וְרוֹצִים לַעֲמֹד בִּתְפִלָּה, יִתְפַּלֵּל עִמָּהֶם וְאַחַר כָּךְ יִקְרָא קְרִיאַת שְׁמַע עִם בִּרְכוֹתֶיהָ.
3 If when he arrived the community had already recited Shema and was standing to pray the Amidah, he should pray the Amidah with them and subsequently recite Shema with its blessings.
ד אַחַר שׁוֹמֵר עַמּוֹ יִשְׂרָאֵל אוֹמֵר אָמֵן אַחַר בִּרְכַּת עַצְמוֹ, וְלֹא יַעֲנֶה אָמֵן אַחַר בִּרְכַּת הַמֶּלֶךְ בִּכְבוֹדוֹ וְעַיֵּן לְעֵיל סִימָן רט"ו.
4 After "shomér amo yisra'él la'ad" [at the end of Hashkivénu], one should say "amen" after that blessing, but should not answer "amen" after the [following] blessing "hamelekh bikhvodo" Rema: "see above at Siman 215."