diff --git a/common/ring_buffer.h b/common/ring_buffer.h
new file mode 100644
index 00000000..7bdebbcf
--- /dev/null
+++ b/common/ring_buffer.h
@@ -0,0 +1,53 @@
+#ifndef RING_BUFFER_H
+#define RING_BUFFER_H
+/*--------------------------------------------------------------------
+ * Ring buffer to store scan codes from keyboard
+ *------------------------------------------------------------------*/
+#define RBUF_SIZE 32
+static uint8_t rbuf[RBUF_SIZE];
+static uint8_t rbuf_head = 0;
+static uint8_t rbuf_tail = 0;
+static inline void rbuf_enqueue(uint8_t data)
+{
+    uint8_t sreg = SREG;
+    cli();
+    uint8_t next = (rbuf_head + 1) % RBUF_SIZE;
+    if (next != rbuf_tail) {
+        rbuf[rbuf_head] = data;
+        rbuf_head = next;
+    } else {
+        print("rbuf: full\n");
+    }
+    SREG = sreg;
+}
+static inline uint8_t rbuf_dequeue(void)
+{
+    uint8_t val = 0;
+
+    uint8_t sreg = SREG;
+    cli();
+    if (rbuf_head != rbuf_tail) {
+        val = rbuf[rbuf_tail];
+        rbuf_tail = (rbuf_tail + 1) % RBUF_SIZE;
+    }
+    SREG = sreg;
+
+    return val;
+}
+static inline bool rbuf_has_data(void)
+{
+    uint8_t sreg = SREG;
+    cli();
+    bool has_data = (rbuf_head != rbuf_tail);
+    SREG = sreg;
+    return has_data;
+}
+static inline void rbuf_clear(void)
+{
+    uint8_t sreg = SREG;
+    cli();
+    rbuf_head = rbuf_tail = 0;
+    SREG = sreg;
+}
+
+#endif  /* RING_BUFFER_H */
diff --git a/converter/ibm4704_usb/config.h b/converter/ibm4704_usb/config.h
index 4f82f49a..812d95c6 100644
--- a/converter/ibm4704_usb/config.h
+++ b/converter/ibm4704_usb/config.h
@@ -56,7 +56,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /*
  * Pin interrupt
  */
-#ifdef IBM4704_USE_INT
 #define IBM4704_INT_INIT()  do {    \
     EICRA |= ((1<<ISC11) |      \
               (0<<ISC10));      \
@@ -68,7 +67,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
     EIMSK &= ~(1<<INT1);        \
 } while (0)
 #define IBM4704_INT_VECT    INT1_vect
-#endif
 
 
 #endif
diff --git a/converter/ibm4704_usb/matrix.c b/converter/ibm4704_usb/matrix.c
index 0bfda2b1..857dea0f 100644
--- a/converter/ibm4704_usb/matrix.c
+++ b/converter/ibm4704_usb/matrix.c
@@ -69,41 +69,34 @@ static void enable_break(void)
 {
     uint8_t ret;
     print("Enable break: ");
-    // valid scancode: 00-77h
-    for (uint8_t code = 0; code < 0x78; code++) {
-        while (ibm4704_send(0x80|code) != 0) {
-            print("z");
-            _delay_us(500);
-        }
-        _delay_us(2000);
-        ret = ibm4704_recv();
-        if (ret != 0xff) {
+    // valid scancode: 00-79h
+    for (uint8_t code = 0; code < 0x7A; code++) {
+        while (ibm4704_send(0x80|code)) _delay_ms(1);
+        // get none when ok, get FD when out of bound
+        _delay_ms(5);
+        if ((ret = ibm4704_recv()) != 0xff) {
             xprintf("c%02X:r%02X ", code, ret);
         }
-        _delay_us(1000);
+        _delay_ms(1);
     }
     _delay_us(1000);
-    while (ibm4704_send(0xFF) != 0) { _delay_us(500); } // End
+    while (ibm4704_send(0xFF)) { _delay_ms(1); } // End
     print("End\n");
 }
 
 void matrix_init(void)
 {
-    uint8_t ret;
-    debug_enable = true;
+    debug_enable = false;
 
     ibm4704_init();
     matrix_clear();
 
-    // read keyboard id
-    while ((ret = ibm4704_recv()) == 0xFF) {
-        ibm4704_send(0xFE);
-        _delay_us(100);
-    }
+    _delay_ms(2000);    // wait for starting up debug console
 
-    _delay_ms(2000);    // wait for starting up debug console 
     print("IBM 4704 converter\n");
-    xprintf("Keyboard ID: %02X\n", ret);
+    while (ibm4704_send(0xFE)) _delay_ms(1);    // resend
+    _delay_ms(5);
+    xprintf("Keyboard ID: %02X\n", ibm4704_recv());
     enable_break();
 }
 
@@ -116,14 +109,16 @@ uint8_t matrix_scan(void)
     if (code==0xFF) {
         // Not receivd
         return 0;
-    } else if ((code&0x78)==0x78) {
-        // 0xFF-F8 and 0x7F-78 is not scancode
-        xprintf("Error: %0X\n", code);
+    } else if ((code&0x7F) >= 0x7A) {
+        // 0xFF-FA and 0x7F-7A is not scancode
+        xprintf("Error: %02X\n", code);
         matrix_clear();
         return 0;
     } else if (code&0x80) {
+        dprintf("%02X\n", code);
         matrix_make(code);
     } else {
+        dprintf("%02X\n", code);
         matrix_break(code);
     }
     return 1;
diff --git a/tmk_core/protocol/ibm4704.c b/tmk_core/protocol/ibm4704.c
index 10e229fd..152d7e61 100644
--- a/tmk_core/protocol/ibm4704.c
+++ b/tmk_core/protocol/ibm4704.c
@@ -4,6 +4,7 @@ Copyright 2010,2011,2012,2013 Jun WAKO <wakojun@gmail.com>
 #include <stdbool.h>
 #include <util/delay.h>
 #include "debug.h"
+#include "ring_buffer.h"
 #include "ibm4704.h"
 
 
@@ -20,7 +21,9 @@ uint8_t ibm4704_error = 0;
 
 void ibm4704_init(void)
 {
-    inhibit();
+    IBM4704_INT_INIT();
+    IBM4704_INT_ON();
+    idle();
 }
 
 /*
@@ -47,6 +50,8 @@ uint8_t ibm4704_send(uint8_t data)
     bool parity = true; // odd parity
     ibm4704_error = 0;
 
+    IBM4704_INT_OFF();
+
     /* Request to send */
     idle();
     clock_lo();
@@ -57,7 +62,6 @@ uint8_t ibm4704_send(uint8_t data)
     /* Data bit */
     for (uint8_t i = 0; i < 8; i++) {
         WAIT(clock_hi, 100, 0x40+i);
-        //_delay_us(5);
         if (data&(1<<i)) {
             parity = !parity;
             data_hi();
@@ -79,28 +83,25 @@ uint8_t ibm4704_send(uint8_t data)
     /* End */
     WAIT(data_lo, 100, 0x36);
 
-    inhibit();
-    _delay_us(200); // wait to recover clock to hi
+    idle();
+    IBM4704_INT_ON();
     return 0;
 ERROR:
-    inhibit();
-    if (ibm4704_error >= 0x30) {
-        xprintf("x%02X ", ibm4704_error);
+    idle();
+    if (ibm4704_error > 0x30) {
+        xprintf("S:%02X ", ibm4704_error);
     }
-    _delay_us(200); // wait to recover clock to hi
+    IBM4704_INT_ON();
     return -1;
 }
 
-/* receive data when host want else inhibit communication */
+/* wait forever to receive data */
 uint8_t ibm4704_recv_response(void)
 {
-    // 250 * 100us(wait start bit in ibm4704_recv)
-    uint8_t data = 0;
-    uint8_t try = 250;
-    do {
-        data = ibm4704_recv();
-    } while (try-- && ibm4704_error);
-    return data;
+    while (!rbuf_has_data()) {
+        _delay_ms(1);
+    }
+    return rbuf_dequeue();
 }
 
 /*
@@ -121,49 +122,69 @@ Stop bit:   Keyboard pulls down Data line to lo after 9th clock.
 */
 uint8_t ibm4704_recv(void)
 {
-    uint8_t data = 0;
-    bool parity = true;    // odd parity
-    ibm4704_error = IBM4704_ERR_NONE;
-
-    idle();
-    _delay_us(5);   // wait for line settles
-
-    /* start bit */
-    WAIT(clock_lo, 100, 0x11); // wait for keyboard to send
-    WAIT(data_hi, 100, 0x12);  // can be delayed that long
-
-    WAIT(clock_hi, 100, 0x13); // first rising edge which can take longer
-    /* data */
-    for (uint8_t i = 0; i < 8; i++) {
-        WAIT(clock_hi, 100, 0x20+i);
-        //_delay_us(5);
-        if (data_in()) {
-            parity = !parity;
-            data |= (1<<i);
-        }
-        WAIT(clock_lo, 150, 0x28+i);
+    if (rbuf_has_data()) {
+        return rbuf_dequeue();
+    } else {
+        return -1;
     }
-
-    /* parity */
-    WAIT(clock_hi, 100, 0x17);
-    if (data_in() != parity) {
-        ibm4704_error = IBM4704_ERR_PARITY;
-        goto ERROR;
-    }
-    WAIT(clock_lo, 150, 0x18);
-
-    /* stop bit */
-    WAIT(clock_hi, 100, 0x19);
-    WAIT(data_lo, 1, 0x19);
-
-    inhibit();
-    _delay_us(200); // wait to recover clock to hi
-    return data;
-ERROR:
-    if (ibm4704_error > 0x12) {
-        xprintf("x%02X ", ibm4704_error);
-    }
-    inhibit();
-    _delay_us(200); // wait to recover clock to hi
-    return -1;
+}
+
+ISR(IBM4704_INT_VECT)
+{
+    static enum {
+        INIT, START, BIT0, BIT1, BIT2, BIT3, BIT4, BIT5, BIT6, BIT7, PARITY,
+    } state = INIT;
+    // LSB first
+    static uint8_t data = 0;
+    // Odd parity
+    static uint8_t parity = false;
+
+    ibm4704_error = 0;
+    // return unless falling edge
+    if (clock_in()) { goto RETURN; }    // why this occurs?
+
+    state++;
+    switch (state) {
+        case START:
+            // Data:Low
+            WAIT(data_hi, 10, state);
+            break;
+        case BIT0:
+        case BIT1:
+        case BIT2:
+        case BIT3:
+        case BIT4:
+        case BIT5:
+        case BIT6:
+        case BIT7:
+            data >>= 1;
+            if (data_in()) {
+                data |= 0x80;
+                parity = !parity;
+            }
+            break;
+        case PARITY:
+            if (data_in()) {
+                parity = !parity;
+            }
+            if (!parity)
+                goto ERROR;
+            rbuf_enqueue(data);
+            ibm4704_error = IBM4704_ERR_NONE;
+            goto DONE;
+            break;
+        default:
+            goto ERROR;
+    }
+    goto RETURN;
+ERROR:
+    ibm4704_error = state;
+    while (ibm4704_send(0xFE)) _delay_ms(1); // resend
+    xprintf("R:%02X\n", data);
+DONE:
+    state = INIT;
+    data = 0;
+    parity = false;
+RETURN:
+    return;
 }