diff --git a/backend/app/services/esp32_spi_slaves.py b/backend/app/services/esp32_spi_slaves.py
index ab6edf85..3188697a 100644
--- a/backend/app/services/esp32_spi_slaves.py
+++ b/backend/app/services/esp32_spi_slaves.py
@@ -301,18 +301,29 @@ class Ssd168xEpaperSlave:
         if 0 <= self._x_byte < self._ram_bpr and 0 <= self._y < self._ram_rows:
             plane[self._y * self._ram_bpr + self._x_byte] = byte
         x_inc = (self._entry_mode & 0x01) == 0x01
+        y_inc = (self._entry_mode & 0x02) == 0x02
+        end_of_row = False
         if x_inc:
             if self._x_byte < self._xrange[1]:
                 self._x_byte += 1
             else:
                 self._x_byte = self._xrange[0]
-                self._y += 1
+                end_of_row = True
         else:
             if self._x_byte > self._xrange[0]:
                 self._x_byte -= 1
             else:
                 self._x_byte = self._xrange[1]
-                self._y += 1
+                end_of_row = True
+        if end_of_row:
+            # Advance Y, WRAPPING at the window boundary like the SSD168x RAM
+            # address counter. Some drivers (e.g. GxEPD2_3C) write the 0x24 then
+            # the 0x26 plane without re-seeking the counter, relying on this
+            # wrap so the second plane lands in the window.
+            if y_inc:
+                self._y = self._yrange[0] if self._y >= self._yrange[1] else self._y + 1
+            else:
+                self._y = self._yrange[1] if self._y <= self._yrange[0] else self._y - 1
 
 
 # ── UC8159c (ACeP 7-colour 5.65" GoodDisplay GDEP0565D90) ───────────────────
diff --git a/frontend/src/simulation/displays/SSD168xDecoder.ts b/frontend/src/simulation/displays/SSD168xDecoder.ts
index 088fcb75..e66178d4 100644
--- a/frontend/src/simulation/displays/SSD168xDecoder.ts
+++ b/frontend/src/simulation/displays/SSD168xDecoder.ts
@@ -374,19 +374,32 @@ export class SSD168xDecoder {
     }
     // Auto-increment per data_entry_mode (default 0x03: X+, then Y+ at end of row).
     const xInc = (this.entryMode & 0x01) === 0x01;
+    const yInc = (this.entryMode & 0x02) === 0x02;
+    let endOfRow = false;
     if (xInc) {
       if (this.xByte < this.xrange[1]) {
         this.xByte += 1;
       } else {
         this.xByte = this.xrange[0];
-        this.y += 1;
+        endOfRow = true;
       }
     } else {
       if (this.xByte > this.xrange[0]) {
         this.xByte -= 1;
       } else {
         this.xByte = this.xrange[1];
-        this.y += 1;
+        endOfRow = true;
+      }
+    }
+    if (endOfRow) {
+      // Advance Y, WRAPPING at the window boundary like the SSD168x RAM address
+      // counter. Some drivers (e.g. GxEPD2_3C) write the 0x24 then the 0x26
+      // plane without re-seeking the counter, relying on this wrap so the
+      // second plane lands in the window.
+      if (yInc) {
+        this.y = this.y >= this.yrange[1] ? this.yrange[0] : this.y + 1;
+      } else {
+        this.y = this.y <= this.yrange[0] ? this.yrange[1] : this.y - 1;
       }
     }
   }
diff --git a/test/test_epaper/ssd168x_decoder.py b/test/test_epaper/ssd168x_decoder.py
index 9445d377..1f0baf90 100644
--- a/test/test_epaper/ssd168x_decoder.py
+++ b/test/test_epaper/ssd168x_decoder.py
@@ -312,17 +312,26 @@ class SSD168xDecoder:
             plane[self._y * self._ram_bpr + self._x_byte] = byte
         # Auto-increment per data_entry_mode (default x+, then y+ at end of row).
         x_inc = (self._entry_mode & 0x01) == 0x01    # bit0: 1 = X+
-        # entry_mode bit1: Y direction; bit2: which counter advances first.
-        # For the default 0x03, X advances; once it hits xrange[1], wrap and Y++.
+        y_inc = (self._entry_mode & 0x02) == 0x02    # bit1: 1 = Y+
+        end_of_row = False
         if x_inc:
             if self._x_byte < self._xrange[1]:
                 self._x_byte += 1
             else:
                 self._x_byte = self._xrange[0]
-                self._y += 1
+                end_of_row = True
         else:
             if self._x_byte > self._xrange[0]:
                 self._x_byte -= 1
             else:
                 self._x_byte = self._xrange[1]
-                self._y += 1
+                end_of_row = True
+        if end_of_row:
+            # Advance Y, WRAPPING at the window boundary like the SSD168x RAM
+            # address counter. Some drivers (e.g. GxEPD2_3C) write the 0x24 then
+            # the 0x26 plane without re-seeking the counter, relying on this wrap
+            # so the second plane lands in the window.
+            if y_inc:
+                self._y = self._yrange[0] if self._y >= self._yrange[1] else self._y + 1
+            else:
+                self._y = self._yrange[1] if self._y <= self._yrange[0] else self._y - 1