diff --git a/python/protocan/periph28335.py b/python/protocan/periph28335.py
new file mode 100644
index 0000000..05a6c04
--- /dev/null
+++ b/python/protocan/periph28335.py
@@ -0,0 +1,98 @@
+"""Portable RS command helpers from Set_Terminal_28335.
+
+The byte order and CRC match ``DTrans.pas``/``UNiiefa.pas``.  This module is
+deliberately UI- and serial-port-independent so desktop and Android clients
+can share the same request builders.
+"""
+
+from __future__ import annotations
+
+
+def crc16_modbus(data: bytes, crc: int = 0xFFFF) -> int:
+    for byte in data:
+        crc ^= byte
+        for _ in range(8):
+            crc = (crc >> 1) ^ 0xA001 if crc & 1 else crc >> 1
+    return crc & 0xFFFF
+
+
+def with_crc(payload: bytes) -> bytes:
+    crc = crc16_modbus(payload)
+    return bytes(payload) + crc.to_bytes(2, "little")
+
+
+def build_read_registers(controller: int, start: int, count: int) -> bytes:
+    _range("Адрес контроллера", controller, 0xFF)
+    _range("Начальный регистр", start, 0xFFFF)
+    if not 1 <= count <= 128 or start + count > 128:
+        raise ValueError("Диапазон регистров должен находиться в 0..127")
+    return with_crc(bytes((controller, 3)) + start.to_bytes(2, "big")
+                    + count.to_bytes(2, "big"))
+
+
+def build_write_register(controller: int, address: int, value: int) -> bytes:
+    _range("Адрес контроллера", controller, 0xFF)
+    _range("Адрес регистра", address, 127)
+    _range("Значение", value, 0xFFFF)
+    return with_crc(bytes((controller, 6)) + address.to_bytes(2, "big")
+                    + value.to_bytes(2, "big"))
+
+
+def build_command(controller: int, command_index: int) -> bytes:
+    if not 0 <= command_index <= 16:
+        raise ValueError("Номер команды должен быть в диапазоне 0..16")
+    value = 1 << command_index if command_index < 16 else 0
+    return build_write_register(controller, 127, value)
+
+
+def expected_read_response_size(count: int) -> int:
+    return count * 2 + 5
+
+
+def decode_read_response(data: bytes, count: int) -> tuple[int, ...]:
+    expected = expected_read_response_size(count)
+    if len(data) != expected:
+        raise ValueError(f"Ожидалось {expected} байт, получено {len(data)}")
+    if crc16_modbus(data[:-2]) != int.from_bytes(data[-2:], "little"):
+        raise ValueError("Ошибка CRC ответа")
+    # Historical replies have a three-byte header; registers are big-endian.
+    body = data[3:-2]
+    if len(body) != count * 2:
+        raise ValueError("Неверная длина данных ответа")
+    return tuple(int.from_bytes(body[offset:offset + 2], "big")
+                 for offset in range(0, len(body), 2))
+
+
+def bits_lsb_first(value: int) -> tuple[bool, ...]:
+    _range("Значение", value, 0xFFFF)
+    return tuple(bool(value & (1 << bit)) for bit in range(16))
+
+
+def word_from_bits(bits) -> int:
+    values = tuple(bool(item) for item in bits)
+    if len(values) != 16:
+        raise ValueError("Должно быть ровно 16 бит")
+    return sum(1 << bit for bit, checked in enumerate(values) if checked)
+
+
+def signed_word(value: int) -> int:
+    _range("Значение", value, 0xFFFF)
+    return value if value < 0x8000 else value - 0x10000
+
+
+def _range(name: str, value: int, maximum: int) -> None:
+    if not 0 <= value <= maximum:
+        raise ValueError(f"{name} вне диапазона 0..{maximum}")
+
+
+PROJECT_COMMANDS = {
+    "По умолчанию": ("Test", "Def", "Save", "Load", "Calibr", "Calcul", "Secret", "Light", "Raw", "-", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "23470": ("Test", "Def", "Save", "Load", "Calibr", "Read", "Secret", "-", "-", "-", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "23550": ("Test", "Def", "Save", "Load", "Calibr", "Read", "Secret", "Send", "-", "-", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "23550.2": ("Test", "Def", "Save", "Load", "Calibr", "Calcul", "Secret", "Send", "Raw", "Beep", "", "", "", "", "Log", "Reset", "Nothing at all"),
+    "ICE 22220.1-3": ("Test", "Zero", "Save", "Def", "Calibr", "Read", "ExtLamp", "ExtLite", "-", "-", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "ICE 22220.4-5": ("Test", "Def", "Save", "Load", "Raw", "Read", "ExtLamp", "ExtLite", "No log", "-", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "Бальзам 161": ("Test", "Zero", "Save", "Def", "Calibr", "Clbr 400", "Stop", "Start", "Init", "Secret", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "Бальзам 162": ("Test", "Def", "Save", "Load", "Calibr", "Secret", "Stop", "Start", "Init", "Tune", "-", "-", "-", "-", "-", "Reset", "Nothing at all"),
+    "Бальзам 163": ("Test", "Def", "Save", "Load", "Calibr", "Calcul", "Stop", "Start", "Init", "Tune", "Secret", "-", "-", "-", "-", "Reset", "Nothing at all"),
+}
diff --git a/python/tests/test_periph28335.py b/python/tests/test_periph28335.py
new file mode 100644
index 0000000..5338089
--- /dev/null
+++ b/python/tests/test_periph28335.py
@@ -0,0 +1,23 @@
+from protocan.periph28335 import (
+    bits_lsb_first, build_command, build_read_registers,
+    build_write_register, crc16_modbus, word_from_bits,
+)
+
+
+def test_read_request_matches_delphi_byte_order():
+    request = build_read_registers(16, 24, 64)
+    assert request[:6] == bytes.fromhex("10 03 00 18 00 40")
+    assert int.from_bytes(request[-2:], "little") == crc16_modbus(request[:-2])
+
+
+def test_write_and_command_use_register_127():
+    request = build_write_register(16, 7, 0x1234)
+    assert request[:6] == bytes.fromhex("10 06 00 07 12 34")
+    command = build_command(16, 15)
+    assert command[:6] == bytes.fromhex("10 06 00 7F 80 00")
+
+
+def test_bits_keep_original_lsb_first_order():
+    bits = bits_lsb_first(0x8005)
+    assert bits[0] and bits[2] and bits[15]
+    assert word_from_bits(bits) == 0x8005