diff --git a/src/engine/platform/ay.cpp b/src/engine/platform/ay.cpp
index 3e53e8fe3..4a70faebc 100644
--- a/src/engine/platform/ay.cpp
+++ b/src/engine/platform/ay.cpp
@@ -427,6 +427,7 @@ int DivPlatformAY8910::dispatch(DivCommand c) {
       chan[c.chan].freqChanged=true;
       break;
     case DIV_CMD_AY_IO_WRITE:
+      if (c.value==255) break;
       if (c.value) { // port B
         ioPortB=true;
         portBVal=c.value2;
diff --git a/src/engine/platform/ay8930.cpp b/src/engine/platform/ay8930.cpp
index 3e114e61b..1849d0cdc 100644
--- a/src/engine/platform/ay8930.cpp
+++ b/src/engine/platform/ay8930.cpp
@@ -100,6 +100,9 @@ const char* DivPlatformAY8930::getEffectName(unsigned char effect) {
     case 0x29:
       return "29xy: Set auto-envelope (x: numerator; y: denominator)";
       break;
+    case 0x2d:
+      return "2Dxx: NOT TO BE EMPLOYED BY THE COMPOSER";
+      break;
     case 0x2e:
       return "2Exx: Write to I/O port A";
       break;
@@ -446,6 +449,10 @@ int DivPlatformAY8930::dispatch(DivCommand c) {
       chan[c.chan].freqChanged=true;
       break;
     case DIV_CMD_AY_IO_WRITE:
+      if (c.value==255) {
+        immWrite(0x1f,c.value2);
+        break;
+      }
       if (c.value) { // port B
         ioPortB=true;
         portBVal=c.value2;
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index 6dddcfcbb..cf02fa6ae 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -730,6 +730,9 @@ bool DivEngine::perSystemPostEffect(int ch, unsigned char effect, unsigned char
         case 0x29: // auto-envelope
           dispatchCmd(DivCommand(DIV_CMD_AY_AUTO_ENVELOPE,ch,effectVal));
           break;
+        case 0x2d: // TEST
+          dispatchCmd(DivCommand(DIV_CMD_AY_IO_WRITE,ch,255,effectVal));
+          break;
         case 0x2e: // I/O port A
           dispatchCmd(DivCommand(DIV_CMD_AY_IO_WRITE,ch,0,effectVal));
           break;