diff --git a/F1:F103/BISS_C_encoders/encoders.bin b/F1:F103/BISS_C_encoders/encoders.bin
index 4940f07..dcf8cfb 100755
Binary files a/F1:F103/BISS_C_encoders/encoders.bin and b/F1:F103/BISS_C_encoders/encoders.bin differ
diff --git a/F1:F103/BISS_C_encoders/encoders.creator.user b/F1:F103/BISS_C_encoders/encoders.creator.user
index ea04e00..efd9972 100644
--- a/F1:F103/BISS_C_encoders/encoders.creator.user
+++ b/F1:F103/BISS_C_encoders/encoders.creator.user
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE QtCreatorProject>
-<!-- Written by QtCreator 17.0.0, 2025-07-15T19:51:56. -->
+<!-- Written by QtCreator 17.0.0, 2025-08-24T23:38:47. -->
 <qtcreator>
  <data>
   <variable>EnvironmentId</variable>
diff --git a/F1:F103/BISS_C_encoders/flash.h b/F1:F103/BISS_C_encoders/flash.h
index 99a164f..2a8266a 100644
--- a/F1:F103/BISS_C_encoders/flash.h
+++ b/F1:F103/BISS_C_encoders/flash.h
@@ -38,6 +38,7 @@ typedef struct{
     uint8_t CPHA : 1;
     uint8_t BR   : 3;
     uint8_t monit: 1; // auto monitoring of encoder each `monittime` milliseconds
+    uint8_t debug: 1; // debug output of read data
 } flags_t;
 
 /*
diff --git a/F1:F103/BISS_C_encoders/main.c b/F1:F103/BISS_C_encoders/main.c
index c75c52d..2cbf7d5 100644
--- a/F1:F103/BISS_C_encoders/main.c
+++ b/F1:F103/BISS_C_encoders/main.c
@@ -54,7 +54,7 @@ static void proc_enc(uint8_t idx){
     char ifacechr = idx ? 'Y' : 'X';
     if(CDCready[iface]){
         int l = USB_receivestr(iface, inbuff, RBINSZ);
-        if(CDCready[I_CMD]){
+        if(CDCready[I_CMD] && the_conf.flags.debug){
             if(l){
                 CMDWR("Enc"); USB_putbyte(I_CMD, ifacechr);
                 CMDWR(": ");
@@ -96,7 +96,7 @@ static void proc_enc(uint8_t idx){
                 if(str) ++gotgood[idx];
                 else ++gotwrong[idx];
             }
-        }else if(!the_conf.flags.monit){
+        }else if(!the_conf.flags.monit && the_conf.flags.debug){
             printResult(&result);
             CMDWR("ENC"); USB_putbyte(I_CMD, ifacechr);
             USB_putbyte(I_CMD, '=');
@@ -118,6 +118,7 @@ static void proc_enc(uint8_t idx){
 
 int main(){
     uint32_t lastT = 0, usartT = 0;
+    uint8_t oldCDCready[bTotNumEndpoints] = {0};
     StartHSE();
     flashstorage_init();
     hw_setup();
@@ -139,6 +140,18 @@ int main(){
             int l = USB_receivestr(I_CMD, inbuff, RBINSZ);
             if(l < 0) CMDWRn("ERROR: CMD USB buffer overflow or string was too long");
             else if(l) parse_cmd(inbuff);
+            // check if interface connected/disconnected
+            // (we CAN'T do much debug output in interrupt functions like linecoding_handler etc, so do it here)
+            for(int i = 0; i < bTotNumEndpoints; ++i){
+                if(oldCDCready[i] != CDCready[i]){
+                    CMDWR("Interface ");
+                    CMDWR(u2str(i));
+                    USB_putbyte(I_CMD, ' ');
+                    if(CDCready[i] == 0) CMDWR("dis");
+                    CMDWRn("connected");
+                    oldCDCready[i] = CDCready[i];
+                }
+            }
         }
         proc_enc(0);
         proc_enc(1);
diff --git a/F1:F103/BISS_C_encoders/proto.c b/F1:F103/BISS_C_encoders/proto.c
index 2a7b315..4fea9ce 100644
--- a/F1:F103/BISS_C_encoders/proto.c
+++ b/F1:F103/BISS_C_encoders/proto.c
@@ -80,6 +80,7 @@ typedef enum{
     C_amperiod,
     C_usart,
     C_ssii,
+    C_debug,
     C_AMOUNT
 } cmd_e;
 
@@ -268,8 +269,6 @@ static errcode_e setuintpar(cmd_e idx, char *par){
                 return ERR_BADCMD;
         }
     }
-    CMDWR(commands[idx].cmd);
-    USB_putbyte(I_CMD, '=');
     switch(idx){
         case C_br:
             val = the_conf.flags.BR;
@@ -295,6 +294,8 @@ static errcode_e setuintpar(cmd_e idx, char *par){
         default:
             return ERR_BADCMD;
     }
+    CMDWR(commands[idx].cmd);
+    USB_putbyte(I_CMD, '=');
     CMDWR(u2str(val));
     CMDn();
     return ERR_SILENCE;
@@ -323,6 +324,9 @@ static errcode_e setboolpar(cmd_e idx, char *par){
             case C_autom:
                 the_conf.flags.monit = val;
                 break;
+            case C_debug:
+                the_conf.flags.debug = val;
+                break;
             default:
                 return ERR_BADCMD;
         }
@@ -343,6 +347,9 @@ static errcode_e setboolpar(cmd_e idx, char *par){
         case C_autom:
             val = the_conf.flags.monit;
             break;
+        case C_debug:
+            val = the_conf.flags.debug;
+            break;
         default:
             return ERR_BADCMD;
     }
@@ -364,6 +371,7 @@ static errcode_e dumpconf(cmd_e _U_ idx, char _U_ *par){
     setuintpar(C_br, NULL);
     setboolpar(C_cpha, NULL);
     setboolpar(C_cpol, NULL);
+    setboolpar(C_debug, NULL);
     setuintpar(C_encbits, NULL);
     setuintpar(C_encbufsz, NULL);
     setuintpar(C_maxzeros, NULL);
@@ -410,6 +418,7 @@ static const funcdescr_t commands[C_AMOUNT] = {
     [C_amperiod] = {"amperiod", setuintpar},
     [C_usart] = {"usart", usart},
     [C_ssii] = {"ssii", setuintpar},
+    [C_debug] = {"debug", setboolpar},
 };
 
 typedef struct{
@@ -434,6 +443,7 @@ static const help_t helpmessages[] = {
     {C_br, "change SPI BR register (1 - 18MHz ... 7 - 281kHz)"},
     {C_cpha, "change CPHA value (0/1)"},
     {C_cpol, "change CPOL value (0/1)"},
+    {C_debug, "turn on debugging output of read encoders' values"},
     {C_dumpconf, "dump current configuration"},
     {C_encbits, "set encoder data bits amount (26/32)"},
     {C_encbufsz, "change encoder auxiliary buffer size (8..32 bytes)"},
@@ -486,6 +496,7 @@ static errcode_e help(_U_ cmd_e idx, _U_ char*  par){
 void parse_cmd(char *cmd){
     errcode_e ecode = ERR_BADCMD;
     // command and its parameter
+CMDWRn(cmd);
     char *cmdstart = omit_spaces(cmd), *parstart = NULL;
     if(!cmdstart) goto retn;
     char *ptr = cmdstart;
@@ -506,5 +517,9 @@ void parse_cmd(char *cmd){
     if(idx >= C_AMOUNT) goto retn; // not found
     ecode = commands[idx].handler(idx, parstart);
 retn:
-    if(ecode != ERR_SILENCE) CMDWRn(errors[ecode]);
+    if(ecode == ERR_BADCMD){
+        CMDWR(cmd);
+        USB_putbyte(I_CMD, '=');
+        CMDWRn(errors[ERR_BADCMD]);
+    } else if(ecode != ERR_SILENCE) CMDWRn(errors[ecode]);
 }
diff --git a/F1:F103/BISS_C_encoders/usb_dev.c b/F1:F103/BISS_C_encoders/usb_dev.c
index aa668a3..fd596e2 100644
--- a/F1:F103/BISS_C_encoders/usb_dev.c
+++ b/F1:F103/BISS_C_encoders/usb_dev.c
@@ -38,6 +38,8 @@
 #define CONTROL_DTR                     0x01
 #define CONTROL_RTS                     0x02
 
+// It's good to use debug here ONLY to debug into USART!
+// never try to debug USB into USB!!!
 #undef DBG
 #define DBG(x)
 #undef DBGs
@@ -141,8 +143,17 @@ void WEAK linecoding_handler(uint8_t ifno, usb_LineCoding *lc){
     lineCoding[ifno] = *lc;
     DBG("linecoding_handler");
     DBGs(uhex2str(ifno));
-    CMDWR("Interface "); CMDWR(u2str(ifno));
-    CMDWR(" got linecoding with speed "); CMDWRn(u2str(lc->dwDTERate));
+}
+
+static void clearbufs(uint8_t ifno){
+    uint32_t T0 = Tms;
+    while(Tms - T0 < 10){ // wait no more than 10ms
+        if(1 == RB_clearbuf((ringbuffer*)&rbin[ifno])) break;
+    }
+    T0 = Tms;
+    while(Tms - T0 < 10){
+        if(1 == RB_clearbuf((ringbuffer*)&rbout[ifno])) break;
+    }
 }
 
 // SET_CONTROL_LINE_STATE
@@ -152,19 +163,14 @@ void WEAK clstate_handler(uint8_t ifno, uint16_t val){
     DBGs(uhex2str(val));
     CDCready[ifno] = val; // CONTROL_DTR | CONTROL_RTS -> interface connected; 0 -> disconnected
     lastdsz[ifno] = -1;
-    if(val == 0) CMDWR("dis");
-    CMDWR("connected interface ");
-    CMDWRn(u2str(ifno));
+    if(val) clearbufs(ifno);
 }
 
-// SEND_BREAK
+// SEND_BREAK - disconnect interface and clear its buffers
 void WEAK break_handler(uint8_t ifno){
     CDCready[ifno] = 0;
-    lastdsz[ifno] = -1;
     DBG("break_handler()");
     DBGs(uhex2str(ifno));
-    CMDWR("Disconnected interface ");
-    CMDWRn(u2str(ifno));
 }
 
 
@@ -297,7 +303,7 @@ int USB_receive(uint8_t ifno, uint8_t *buf, int len){
     if(bufovrfl[ifno]){
         DBG("Buffer overflow");
         DBGs(uhex2str(ifno));
-        while(1 != RB_clearbuf((ringbuffer*)&rbin[ifno]));
+        while(1 != RB_clearbuf((ringbuffer*)&rbin[ifno])); // run watchdog in case of problems
         bufovrfl[ifno] = 0;
         return -1;
     }
diff --git a/F1:F103/BISS_C_encoders/version.inc b/F1:F103/BISS_C_encoders/version.inc
index 2f05971..d66eb33 100644
--- a/F1:F103/BISS_C_encoders/version.inc
+++ b/F1:F103/BISS_C_encoders/version.inc
@@ -1,2 +1,2 @@
-#define BUILD_NUMBER "111"
-#define BUILD_DATE "2025-07-15"
+#define BUILD_NUMBER "126"
+#define BUILD_DATE "2025-08-24"