diff --git a/converter/pc98_usb/README b/converter/pc98_usb/README
index 24200d83..4d0d0bfe 100644
--- a/converter/pc98_usb/README
+++ b/converter/pc98_usb/README
@@ -147,6 +147,7 @@ Its scan code map is very different from standard types. This is not tested.
 Other PC98 converter projects and resource
 ------------------------------------------
 PC-9800シリーズ テクニカルデータブック HARDWARE 編 1993年 p139, p343
+https://archive.org/stream/PC9800TechnicalDataBookHARDWARE1993/PC-9800TechnicalDataBook_HARDWARE1993#page/n151
 https://archive.org/stream/PC9800TechnicalDataBookHARDWARE1993/PC-9800TechnicalDataBook_HARDWARE1993#page/n355
 
 PC98 to USB
@@ -158,3 +159,25 @@ http://www.tsp.ne.jp/~sawada/mago/src/gka98at.asm
 
 scan code:
 http://ixsvr.dyndns.org/usb2pc98
+
+
+
+NOTES
+-----
+### Tested on
+- PC-9801V
+- DIGITAL WAVE Dboard
+
+
+### RDY
+Current firmware does not control RDY line and it is drived as low to receive data always. While sending command firmware drive the line high.
+
+PC98 host keeps RDY line high to prevent keyboard from sending data while processing.
+
+https://archive.org/stream/PC9800TechnicalDataBookHARDWARE1993/PC-9800TechnicalDataBook_HARDWARE1993#page/n359
+
+### Inhibit key repeating
+The command(9Ch, 70h) works with Raku Raku keybaord but not with Dboard.
+
+### LED indicater
+Dboard has LEDs but it seems to ignore LED control command.
diff --git a/converter/pc98_usb/config.h b/converter/pc98_usb/config.h
index c6315d00..c74b434b 100644
--- a/converter/pc98_usb/config.h
+++ b/converter/pc98_usb/config.h
@@ -43,7 +43,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define LOCKING_RESYNC_ENABLE
 
 /* Control LED indicatiors, which doesn't work well with locking support */
-//#define PC98_LED_CONTROL
+#define PC98_LED_CONTROL
 
 
 /* PC98 Reset Port shared with TXD */
diff --git a/converter/pc98_usb/matrix.c b/converter/pc98_usb/matrix.c
index 54bb3041..39afb43c 100644
--- a/converter/pc98_usb/matrix.c
+++ b/converter/pc98_usb/matrix.c
@@ -68,23 +68,34 @@ static int16_t pc98_wait_response(void)
 static void pc98_inhibit_repeat(void)
 {
     uint16_t code;
-
-    // clear recv buffer
-    while (serial_recv()) ;
 RETRY:
-    _delay_ms(100);
     pc98_send(0x9C);
     code = pc98_wait_response();
     if (code != -1) xprintf("PC98: send 9C: %02X\n", code);
     if (code != 0xFA) goto RETRY;
 
-    _delay_ms(100);
     pc98_send(0x70);
     code = pc98_wait_response();
     if (code != -1) xprintf("PC98: send 70: %02X\n", code);
     if (code != 0xFA) goto RETRY;
 }
 
+static uint8_t pc98_led = 0;
+static void pc98_led_set(void)
+{
+    uint16_t code;
+RETRY:
+    pc98_send(0x9D);
+    code = pc98_wait_response();
+    if (code != -1) xprintf("PC98: send 9D: %02X\n", code);
+    if (code != 0xFA) goto RETRY;
+
+    pc98_send(pc98_led);
+    code = pc98_wait_response();
+    if (code != -1) xprintf("PC98: send %02X: %02X\n", pc98_led, code);
+    if (code != 0xFA) goto RETRY;
+}
+
 void matrix_init(void)
 {
     debug_keyboard = true;
@@ -99,36 +110,40 @@ void matrix_init(void)
     serial_init();
 
     // PC98 reset
-/*
-    PC98_RST_PORT &= ~(1<<PC98_RST_BIT);
-    _delay_us(15);
-    PC98_RST_PORT |= (1<<PC98_RST_BIT);
-    _delay_us(13);
-    PC98_RDY_PORT &= ~(1<<PC98_RDY_BIT);
-*/
+    // https://archive.org/stream/PC9800TechnicalDataBookHARDWARE1993/PC-9800TechnicalDataBook_HARDWARE1993#page/n359
+    PC98_RDY_PORT |=  (1<<PC98_RDY_BIT);    // RDY: high
+    PC98_RST_PORT &= ~(1<<PC98_RST_BIT);    // RST: low
+    _delay_us(15);                          // > 13us
+    PC98_RST_PORT |= (1<<PC98_RST_BIT);     // RST: high
 
-    _delay_ms(500);
+    _delay_ms(50);
     pc98_inhibit_repeat();
 
-
-    // PC98 ready
-    PC98_RDY_PORT &= ~(1<<PC98_RDY_BIT);
-
     // initialize matrix state: all keys off
     for (uint8_t i=0; i < MATRIX_ROWS; i++) matrix[i] = 0x00;
 
-    debug("init\n");
+    // ready to receive from keyboard
+    PC98_RDY_PORT &= ~(1<<PC98_RDY_BIT);    // RDY: low
+
+    print("matrix_init done.\n");
     return;
 }
 
 uint8_t matrix_scan(void)
 {
     uint16_t code;
-    PC98_RDY_PORT |= (1<<PC98_RDY_BIT);
-    //_delay_us(30);
     code = serial_recv2();
-    PC98_RDY_PORT &= ~(1<<PC98_RDY_BIT);
-    if (code == -1) return 0;
+    if (code == -1) {
+#ifdef PC98_LED_CONTROL
+        // Before sending command  we have to make sure that there is no unprocessed key in queue
+        // otherwise keys will be missed during sending command
+        if (pc98_led) {
+            pc98_led_set();
+            pc98_led = 0;
+        }
+#endif
+        return 0;
+    }
 
     print_hex8(code); print(" ");
 
@@ -154,15 +169,11 @@ uint8_t matrix_get_row(uint8_t row)
 
 void led_set(uint8_t usb_led)
 {
-#ifdef PC98_LED_CONTROL
-    uint8_t led_state = 0x70;
-    if (usb_led & (1<<USB_LED_NUM_LOCK))    led_state |= (1<<0);
-    if (usb_led & (1<<USB_LED_CAPS_LOCK))   led_state |= (1<<2);
-    xprintf("led_set: %02X\n", led_state);
-
-    pc98_send(0x9D);
-    _delay_ms(100);
-    pc98_send(led_state);
-    // responses(FA or FC) will be ignored in matrix_scan()
-#endif
+    // https://archive.org/stream/PC9800TechnicalDataBookHARDWARE1993/PC-9800TechnicalDataBook_HARDWARE1993#page/n161
+    // http://www.webtech.co.jp/company/doc/undocumented_mem/io_kb.txt
+    pc98_led = 0x70;
+    if (usb_led & (1<<USB_LED_NUM_LOCK))    pc98_led |= (1<<0);
+    if (usb_led & (1<<USB_LED_CAPS_LOCK))   pc98_led |= (1<<2);
+    xprintf("usb_led: %02X\n", usb_led);
+    xprintf("pc98_led: %02X\n", pc98_led);
 }