{
  "id": "terminal-csi/su",
  "family": "terminal-csi",
  "slug": "su",
  "title": "CSI SU / SD — Scroll Up / Scroll Down (pan)",
  "summary": "SU (final 'S') scrolls the contents of the scroll region up by Pn lines (new blank lines appear at the bottom); SD (final 'T') scrolls down by Pn lines (blank lines appear at the top). The cursor position is unchanged. Both default Pn to 1.",
  "kind": "control-sequence",
  "aliases": [
    "SU",
    "SD",
    "scroll up",
    "scroll down",
    "pan up",
    "pan down",
    "ESC [ S",
    "ESC [ T"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://invisible-island.net/xterm/ctlseqs/ctlseqs.html",
  "source_version": "xterm ctlseqs, patch #410, 2026/04/19",
  "retrieved_date": "2026-05-29",
  "attribution": [
    {
      "claim_ref": "#summary",
      "source_url": "https://invisible-island.net/xterm/ctlseqs/ctlseqs.html",
      "source_version": "xterm patch #410, 2026/04/19",
      "note": "xterm ctlseqs: CSI Ps S = Scroll up Ps lines (SU); CSI Ps T = Scroll down Ps lines (SD). Default Ps = 1. (Note: CSI Ps ; Ps ; ... T with parameters is the xterm mouse highlight-tracking initiation, distinct from bare SD.)"
    },
    {
      "claim_ref": "ext.params",
      "source_url": "https://ecma-international.org/publications-and-standards/standards/ecma-48/",
      "source_version": "ECMA-48 5th ed. 1991 (ISO/IEC 6429), clauses 8.3.147 (SU) and 8.3.113 (SD)",
      "note": "ECMA-48 defines SU (final 'S') and SD (final 'T') as scrolling the page/region by Pn lines, default 1."
    }
  ],
  "see_also": [
    "terminal-csi/il",
    "terminal-csi/decstbm",
    "terminal-csi/ed"
  ],
  "ext_type": "terminal-escape@1",
  "ext": {
    "csi_or_osc": "CSI",
    "command_number": "SU",
    "frame": {
      "introducer_7bit": "\u001b[",
      "introducer_7bit_readable": "ESC [ (0x1B 0x5B)",
      "introducer_8bit": "›",
      "introducer_8bit_readable": "0x9B (single-byte CSI, 8-bit C1)",
      "note": "CSI + single Pn + final byte: 'S' scroll-up (0x53), 'T' scroll-down (0x54). Pn defaults to 1; scoped to the scroll region."
    },
    "terminator": "none",
    "terminator_detail": {
      "note": "No string terminator; the CSI sequence ends at its final byte. Parameters Ps are decimal, ';' (0x3B) separated."
    },
    "params": [
      {
        "id": "su",
        "anchor": "#su",
        "name": "SU — Scroll Up (S)",
        "meaning": "CSI Pn S scrolls the scroll region up Pn lines; the top Pn lines scroll off and Pn blank lines appear at the bottom. The cursor stays put.",
        "required": true,
        "byte_sequence_ST": "\u001b[2S",
        "byte_sequence_ST_readable": "ESC [ 2 S   ==  \\x1b[2S   (scroll up 2 lines)",
        "subparams": []
      },
      {
        "id": "sd",
        "anchor": "#sd",
        "name": "SD — Scroll Down (T)",
        "meaning": "CSI Pn T scrolls the scroll region down Pn lines; the bottom Pn lines scroll off and Pn blank lines appear at the top.",
        "required": false,
        "byte_sequence_ST": "\u001b[2T",
        "byte_sequence_ST_readable": "ESC [ 2 T   ==  \\x1b[2T   (scroll down 2 lines)",
        "subparams": []
      }
    ],
    "gotchas": [
      "BARE 'CSI Ps T' (one parameter) is SD; but 'CSI Ps ; Ps ; Ps ; Ps ; Ps T' (five parameters) is xterm's Initiate Highlight Mouse Tracking — parameter count disambiguates. Avoid emitting SD with stray extra parameters.",
      "SU/SD pan the SCROLL REGION (DECSTBM); content outside the region is not moved.",
      "New blank lines take the current SGR background color.",
      "The cursor position is unchanged by SU/SD, unlike LF/RI which can move the cursor.",
      "Pn of 0 is treated as 1."
    ],
    "v1_smoke_test": {
      "asserts": "SU ('S') and SD ('T') render as byte-exact single-parameter CSI sequences; the SD-vs-mouse-highlight ambiguity is noted.",
      "behavioral_conformance": "deferred to v2."
    }
  },
  "updated": "2026-05-29T00:00:00Z"
}