diff --git a/README.md b/README.md
index af549ea..d83451d 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@
 
 | Mode | Description |
 |------|-------------|
-| **I2C** (default) | I2C slave reports characters / key data to the host. |
+| **I2C** (default) | I2C slave reports characters / key data to the host. Enter sends CardKB CR (`0x0D`). Fn+D/X/Z/C emit CardKB navigation codes (`0xB5`/`0xB6`/`0xB4`/`0xB7`) for host UI navigation (e.g. Meshtastic). |
 | **UART** | Custom frames with key index and press / release over UART. |
 | **ESP-NOW** | Broadcasts key frames (similar framing to UART). |
 | **BLE HID** | Bluetooth HID keyboard, including arrow keys via Fn combos. |
diff --git a/src/main/app/app_factory.c b/src/main/app/app_factory.c
index 1e8a233..5c6136b 100644
--- a/src/main/app/app_factory.c
+++ b/src/main/app/app_factory.c
@@ -700,37 +700,45 @@ static void app_process_key_event(key_event_t *key_event)
     if (is_press && fn_pressed) {
         switch (key_event->button_index) {
             case KEY_UP:  // Fn+D = 上方向键
-                if (g_mode == MODE_BLEHID) {
+                if (g_mode == MODE_I2C) {
+                    bsp_i2c_add_key(KEYCODE_ARROW_UP);
+                } else if (g_mode == MODE_BLEHID) {
                     if (bsp_blehid_is_connected()) {
                         bsp_blehid_send_keycode(0, USB_HID_KEY_UP);
                     }
                 }
                 return;
-                
+
             case KEY_LEFT:  // Fn+Z = 左方向键
-                if (g_mode == MODE_BLEHID) {
+                if (g_mode == MODE_I2C) {
+                    bsp_i2c_add_key(KEYCODE_ARROW_LEFT);
+                } else if (g_mode == MODE_BLEHID) {
                     if (bsp_blehid_is_connected()) {
                         bsp_blehid_send_keycode(0, USB_HID_KEY_LEFT);
                     }
                 }
                 return;
-                
+
             case KEY_DOWN:  // Fn+X = 下方向键
-                if (g_mode == MODE_BLEHID) {
+                if (g_mode == MODE_I2C) {
+                    bsp_i2c_add_key(KEYCODE_ARROW_DOWN);
+                } else if (g_mode == MODE_BLEHID) {
                     if (bsp_blehid_is_connected()) {
                         bsp_blehid_send_keycode(0, USB_HID_KEY_DOWN);
                     }
                 }
                 return;
-                
+
             case KEY_RIGHT:  // Fn+C = 右方向键
-                if (g_mode == MODE_BLEHID) {
+                if (g_mode == MODE_I2C) {
+                    bsp_i2c_add_key(KEYCODE_ARROW_RIGHT);
+                } else if (g_mode == MODE_BLEHID) {
                     if (bsp_blehid_is_connected()) {
                         bsp_blehid_send_keycode(0, USB_HID_KEY_RIGHT);
                     }
                 }
                 return;
-                
+
             default:
                 break;
         }
@@ -760,7 +768,12 @@ static void app_process_key_event(key_event_t *key_event)
         char key_char = 0;
         if (app_get_key_char(key_event->button_index, &key_char)) {
             if (g_mode == MODE_I2C) {
-                bsp_i2c_add_key((uint8_t)key_char);
+                uint8_t i2c_key = (uint8_t)key_char;
+                // CardKB hosts (e.g. Meshtastic) expect CR for Enter, not LF from keymap
+                if (i2c_key == 0x0A || key_event->button_index == KEY_ENTER) {
+                    i2c_key = KEYCODE_ENTER;
+                }
+                bsp_i2c_add_key(i2c_key);
             } else if (g_mode == MODE_BLEHID) {
                 if (bsp_blehid_is_connected()) {
                     bsp_blehid_send_key(key_char);
diff --git a/src/main/app/app_factory.h b/src/main/app/app_factory.h
index 6f9cc83..ff34109 100644
--- a/src/main/app/app_factory.h
+++ b/src/main/app/app_factory.h
@@ -57,6 +57,13 @@ typedef struct {
 #define KEY_DOWN         36 // 下方向键 (行3, 列3) = 3*11+3 = 36 (Fn+X)
 #define KEY_RIGHT        37 // 右方向键 (行3, 列4) = 3*11+4 = 37 (Fn+C)
 
+// Original M5Stack CardKB I2C navigation key codes (used by Meshtastic and other hosts)
+#define KEYCODE_ENTER        0x0D
+#define KEYCODE_ARROW_LEFT   0xB4
+#define KEYCODE_ARROW_UP     0xB5
+#define KEYCODE_ARROW_DOWN   0xB6
+#define KEYCODE_ARROW_RIGHT  0xB7
+
 // 输出模式选择：1=DEBUG模式(输出index), 0=正常模式(输出ASCII)
 #define KEYBOARD_DEBUG_MODE   0