diff --git a/cmdtab.h b/cmdtab.h
index 0ca51b94..4306b042 100644
--- a/cmdtab.h
+++ b/cmdtab.h
@@ -1673,7 +1673,7 @@
   "Format: \"t?\" displays whether instruction tracing is on or off\n"          \
   "and the address range if any.\n"
 
-#define tckd_cmd_desc           "Turn CKD_KEY tracing on/off"
+#define tckd_cmd_desc           "Turn CKD Search Key tracing on/off"
 #define odev_cmd_desc           "Turn ORB tracing on/off"
 #define tdev_cmd_desc           "Turn CCW tracing on/off"
 #define tplus_cmd_desc          "Turn on instruction tracing"
@@ -2082,7 +2082,7 @@ COMMAND( "f{+/-}adr",               NULL,                   SYSCMDNOPER,
 COMMAND( "o{+/-}dev",               NULL,                   SYSCMDNOPER,        odev_cmd_desc,          NULL                )
 COMMAND( "t{+/-}dev",               NULL,                   SYSCMDNOPER,        tdev_cmd_desc,          NULL                )
 #if defined( OPTION_CKD_KEY_TRACING )
-COMMAND( "t{+/-}CKD",               NULL,                   SYSCMDNOPER,        tckd_cmd_desc,          NULL                )
+COMMAND( "t{+/-}CKD [devnum]",      NULL,                   SYSCMDNOPER,        tckd_cmd_desc,          NULL                )
 #endif
         // PROGRAMMING NOTE: the following CCKD 'sf' shadow file commands
         // are directly routed by the 'CallHercCmd' function in "cmdtab.c".
diff --git a/dasdtab.c b/dasdtab.c
index 1326d473..7a614c26 100644
--- a/dasdtab.c
+++ b/dasdtab.c
@@ -408,7 +408,8 @@ int altcyls;                            /* Number alternate cyls     */
       (cu->devt == 0x3990 &&                    // ... or in 24-byte sense
        ckd->devt == 0x3380));                   // ... compatibility for 3380
                                                 // ... hosted on 3990 controller
-    devchar[10] = ckd->devclass;                // Device class code
+    devchar[10] = ckd->devclass;                // Device class code:
+                                                // (always X'20'=DASD)
     devchar[11] = ckd->code;                    // Device type code
     store_hw(devchar+12, cyls - altcyls);       // Primary cylinders
     store_hw(devchar+14, ckd->heads);           // Tracks per cylinder
diff --git a/dasdtab.h b/dasdtab.h
index 9eb43ffc..b909cc21 100644
--- a/dasdtab.h
+++ b/dasdtab.h
@@ -41,7 +41,8 @@ typedef struct _CKDDEV {                /* CKD Device table entry    */
   const char   *name;                   /* Device name               */
         U16     devt;                   /* Device type               */
         BYTE    model;                  /* Device model              */
-        BYTE    devclass;               /* Device class              */
+        BYTE    devclass;               /* Device class: X'20'=DASD  */
+#define DEVCLASS_DASD       0x20
         BYTE    code;                   /* Device code               */
         U16     cyls;                   /* Number primary cylinders  */
         U16     altcyls;                /* Number alternate cylinders*/
diff --git a/hsccmd.c b/hsccmd.c
index 8570e815..5c31e9ac 100644
--- a/hsccmd.c
+++ b/hsccmd.c
@@ -8034,7 +8034,7 @@ static int fonoff_cmd( REGS* regs, char* cmdline )
 /*-------------------------------------------------------------------*/
 int OnOffCommand( int argc, char* argv[], char* cmdline )
 {
-    char*   cmd = cmdline;              /* Copy of panel command     */
+    char*   cmd = cmdline;              /* (just a shorter name)     */
     bool    plus_enable_on;             /* true == x+, false == x-   */
     char*   onoroff;                    /* x+ == "on", x- == "off"   */
     DEVBLK* dev;
@@ -8057,82 +8057,160 @@ int OnOffCommand( int argc, char* argv[], char* cmdline )
     }
 
     OBTAIN_INTLOCK( NULL );
-
-    if (!IS_CPU_ONLINE( sysblk.pcpu ))
     {
-        RELEASE_INTLOCK( NULL );
-        // "Processor %s%02X: processor is not %s"
-        WRMSG( HHC00816, "W", PTYPSTR( sysblk.pcpu ), sysblk.pcpu, "online" );
-        return 0;
-    }
+        if (!IS_CPU_ONLINE( sysblk.pcpu ))
+        {
+            RELEASE_INTLOCK( NULL );
+            // "Processor %s%02X: processor is not %s"
+            WRMSG( HHC00816, "W", PTYPSTR( sysblk.pcpu ), sysblk.pcpu, "online" );
+            return 0;
+        }
 
-    regs = sysblk.regs[ sysblk.pcpu ];
+        regs = sysblk.regs[ sysblk.pcpu ];
 
-    // f- and f+ commands - mark 4K page frame as -unusable or +usable
+        // f- and f+ commands - mark 4K page frame as -unusable or +usable
 
-    if (cmd[0] == 'f')
-    {
-        int rc = fonoff_cmd( regs, cmdline );
-        RELEASE_INTLOCK( NULL );
-        return rc;
-    }
+        if (cmd[0] == 'f')
+        {
+            int rc = fonoff_cmd( regs, cmdline );
+            RELEASE_INTLOCK( NULL );
+            return rc;
+        }
 
 #if defined( OPTION_CKD_KEY_TRACING )
 
-    // t+ckd and t-ckd commands - turn CKD_KEY tracing on/off
+        // t+ckd [devnum] and t-ckd [devnum] commands - turn CKD Search Key tracing on/off
 
-    if ((cmd[0] == 't') && (strcasecmp(cmd+2, "ckd") == 0))
-    {
-        for (dev = sysblk.firstdev; dev != NULL; dev = dev->nextdev)
+        if (1
+            && (cmd[0] == 't')
+            && (cmd[2] == 'c' || cmd[2] == 'C')
+            && (cmd[3] == 'k' || cmd[3] == 'K')
+            && (cmd[4] == 'd' || cmd[4] == 'D')
+            && (cmd[5] ==  0  || cmd[5] == ' ')
+        )
         {
-            if (dev->devchar[10] == 0x20)
+            char buf[64];   // (results message buffer)
+
+            if (cmd[5] ==  0) // (just "t+ckd" without any device number)
+            {
+                // Enable CKD Search Key tracing for all CKD devices...
+
+                bool bFound = false;
+
+                for (dev = sysblk.firstdev; dev != NULL; dev = dev->nextdev)
+                {
+                    if (dev->devchar[10] == DEVCLASS_DASD)
+                    {
+                        bFound = true;
+                        dev->ckdkeytrace = plus_enable_on;
+                    }
+                }
+
+                if (!bFound)
+                {
+                    RELEASE_INTLOCK( NULL );
+                    // "No dasd devices found"
+                    WRMSG( HHC02226, "E" );
+                    return -1;
+                }
+
+                // Build results message
+                MSGBUF( buf, "%s for all dasd devices", onoroff );
+            }
+            else if (cmd[5] != ' ')
+            {
+                RELEASE_INTLOCK( NULL );
+                // "Invalid argument %s%s"
+                WRMSG( HHC02205, "E", cmd, "" );
+                return -1;
+            }
+            else // (optional device number presumably specified)
+            {
+                const char* p;
+                U16 lcss, devnum;
+
+                // Position to start of devnum operand
+                for (p = &cmd[6]; *p && *p == ' '; ++p);
+
+                // Parse the device number
+                if (parse_single_devnum( p, &lcss, &devnum ) < 0)
+                {
+                    RELEASE_INTLOCK( NULL );
+                    return -1;  // (error message already displayed)
+                }
+
+                // Validate device number
+                if (!(dev = find_device_by_devnum( lcss, devnum )))
+                {
+                    RELEASE_INTLOCK( NULL );
+                    // HHC02200 "%1d:%04X device not found"
+                    devnotfound_msg( lcss, devnum );
+                    return -1;
+                }
+
+                if (dev->devchar[10] != DEVCLASS_DASD)
+                {
+                    RELEASE_INTLOCK( NULL );
+                    // "%1d:%04X is not a dasd device"
+                    WRMSG( HHC02225, "E", lcss, devnum );
+                    return -1;
+                }
+
+                // Enable CKD Search Key tracing for this device
                 dev->ckdkeytrace = plus_enable_on;
+
+                // Build results message
+                MSGBUF( buf, "%s for device %1d:%04X", onoroff, lcss, devnum );
+            }
+
+            RELEASE_INTLOCK( NULL );
+
+            // "%-14s set to %s"
+            WRMSG( HHC02204, "I", "CKD key trace", buf );
+            return 0;
         }
-        RELEASE_INTLOCK( NULL );
-        WRMSG( HHC02204, "I", "CKD key trace", onoroff );
-        return 0;
-    }
 
 #endif
 
-    // o+devn and o-devn commands - turn ORB tracing on/off
-    // t+devn and t-devn commands - turn CCW tracing on/off
+        // o+devn and o-devn commands - turn ORB tracing on/off
+        // t+devn and t-devn commands - turn CCW tracing on/off
 
-    if (1
-        && (cmd[0] == 'o' || cmd[0] == 't')
-        && parse_single_devnum_silent( &cmd[2], &lcss, &devnum ) == 0
-    )
-    {
-        char* typ;
-        char buf[40];
-
-        if (!(dev = find_device_by_devnum( lcss, devnum )))
+        if (1
+            && (cmd[0] == 'o' || cmd[0] == 't')
+            && parse_single_devnum_silent( &cmd[2], &lcss, &devnum ) == 0
+        )
         {
-            // HHC02200 "%1d:%04X device not found"
-            devnotfound_msg( lcss, devnum );
+            char* typ;
+            char buf[40];
+
+            if (!(dev = find_device_by_devnum( lcss, devnum )))
+            {
+                // HHC02200 "%1d:%04X device not found"
+                devnotfound_msg( lcss, devnum );
+                RELEASE_INTLOCK( NULL );
+                return -1;
+            }
+
+            if (cmd[0] == 'o')
+            {
+                typ = "ORB trace";
+                dev->orbtrace = plus_enable_on;
+            }
+            else // (cmd[0] == 't')
+            {
+                typ = "CCW trace";
+                dev->orbtrace = plus_enable_on;
+                dev->ccwtrace = plus_enable_on;
+            }
+            MSGBUF( buf, "%s for %1d:%04X", typ, lcss, devnum );
+            // "%-14s set to %s"
+            WRMSG( HHC02204, "I", buf, onoroff );
             RELEASE_INTLOCK( NULL );
-            return -1;
+            return 0;
         }
-
-        if (cmd[0] == 'o')
-        {
-            typ = "ORB trace";
-            dev->orbtrace = plus_enable_on;
-        }
-        else // (cmd[0] == 't')
-        {
-            typ = "CCW trace";
-            dev->orbtrace = plus_enable_on;
-            dev->ccwtrace = plus_enable_on;
-        }
-        MSGBUF( buf, "%s for %1d:%04X", typ, lcss, devnum );
-        // "%-14s set to %s"
-        WRMSG( HHC02204, "I", buf, onoroff );
-        RELEASE_INTLOCK( NULL );
-        return 0;
     }
-
     RELEASE_INTLOCK( NULL );
+
     // "Invalid argument %s%s"
     WRMSG( HHC02205, "E", cmd, "" );
     return -1;
diff --git a/html/hercinst.html b/html/hercinst.html
index 795d725d..1f6440bd 100644
--- a/html/hercinst.html
+++ b/html/hercinst.html
@@ -1132,7 +1132,7 @@ panel commands:
      tt32                 *Control/query CTCI-WIN functionality
      txf                  *Transactional-Execution Facility tracing
      tzoffset              Set tzoffset parameter
-     t{+/-}CKD             Turn CKD_KEY tracing on/off
+     t{+/-}CKD [devnum]    Turn CKD Search Key tracing on/off
      t{+/-}dev             Turn CCW tracing on/off
      u                    *Disassemble storage
      uptime                Display how long Hercules has been running
diff --git a/msgenu.h b/msgenu.h
index f4c88cbf..234ffaa8 100644
--- a/msgenu.h
+++ b/msgenu.h
@@ -1357,8 +1357,8 @@ LOGM_DLL_IMPORT int  panel_command_capture( char* cmd, char** resp, bool quiet )
 #define HHC02222 "Unsupported function"
 #define HHC02223 "%s of %s-labeled volume %s pending for drive %u:%4.4X %s"
 #define HHC02224 "Store status rejected: CPU not stopped"
-//efine HHC02225 (available)
-//efine HHC02226 (available)
+#define HHC02225 "%1d:%04X is not a dasd device"
+#define HHC02226 "No dasd devices found"
 #define HHC02227 "Shell/Exec commands are disabled"
 #define HHC02228 "%s key pressed"
 #define HHC02229 "Instruction %s %s%s%s"