diff --git a/ubitx_20/cat_libs.ino b/ubitx_20/cat_libs.ino
index e467f1b..13b3ab4 100644
--- a/ubitx_20/cat_libs.ino
+++ b/ubitx_20/cat_libs.ino
@@ -54,6 +54,32 @@
 #define EEPROM_READ_PREFIX 0xE0
 #define EEPROM_WRITE_PREFIX 0xF0
 
+#define IOP_MODE_COMMAND  0x00
+#define IOP_MODE_SSB      0x01
+#define IOP_MODE_DIGI     0x02
+#define IOP_MODE_CW       0x03
+
+/*
+ * KC4UPR - IOP update, 2020-05-03
+ * 
+ * Send the current mode to the I/O Processor.
+ * 
+ * NOTE:  This all needs to be expanded to include digital...
+ * 
+ * NOTE:  Not yet called from CAT, only from menu...
+ */
+void iopSendMode(char is_cw, char is_usb) 
+{
+  byte mode;
+  
+  Serial.write(IOP_PREFIX | 2);
+  Serial.write(IOP_MODE_COMMAND);
+  if (is_cw)
+    mode = IOP_MODE_CW;
+  else
+    mode = IOP_MODE_SSB;
+}
+
 unsigned int skipTimeCount = 0;
 byte CAT_BUFF[5];
 byte CAT_SNDBUFF[5];
diff --git a/ubitx_20/ubitx_menu.ino b/ubitx_20/ubitx_menu.ino
index 502bd94..4bec378 100644
--- a/ubitx_20/ubitx_menu.ino
+++ b/ubitx_20/ubitx_menu.ino
@@ -960,6 +960,8 @@ void menuSelectMode(int btn){
       else if (selectModeType == 3) {
         cwMode = 2;
       }
+      // KC4UPR: sending mode to IOP
+      iopSendMode(cwMode, isUSB);
 
       FrequencyToVFO(1);
     }