diff --git a/armsrc/iso15693.c b/armsrc/iso15693.c
index 39c52e97b..b9264fd9f 100644
--- a/armsrc/iso15693.c
+++ b/armsrc/iso15693.c
@@ -107,7 +107,7 @@
 ///////////////////////////////////////////////////////////////////////
 
 // buffers
-#define ISO15693_MAX_RESPONSE_LENGTH     2116 // allows read multiple block with the maximum block size of 256bits and a maximum block number of 64 with REQ_OPTION (lock status for each block
+#define ISO15693_MAX_RESPONSE_LENGTH     2116 // allows read multiple block with the maximum block size of 256bits and a maximum block number of 64 with REQ_OPTION (lock status for each block).
 #define ISO15693_MAX_COMMAND_LENGTH      45 // allows write single block with the maximum block size of 256bits. Write multiple blocks not supported yet
 
 // 32 + 2 crc + 1
@@ -1201,42 +1201,39 @@ static int RAMFUNC Handle15693SampleFromReader(bool bit, DecodeReader_t *reader)
             break;
 
         case STATE_READER_AWAIT_1ST_RISING_EDGE_OF_SOF:
-            reader->posCount++;
             if (bit) { // detected rising edge
-                if (reader->posCount < 4) { // rising edge too early (nominally expected at 5)
+                if (reader->posCount < 2) { // rising edge too early (nominally expected at 4)
                     reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
                 } else { // SOF
                     reader->state = STATE_READER_AWAIT_2ND_FALLING_EDGE_OF_SOF;
+                    reader->posCount = 1;
                 }
             } else {
-                if (reader->posCount > 5) { // stayed low for too long
+                reader->posCount++;
+                if (reader->posCount > 6) { // stayed low for too long
                     DecodeReaderReset(reader);
-                } else {
-                    // do nothing, keep waiting
                 }
             }
             break;
 
         case STATE_READER_AWAIT_2ND_FALLING_EDGE_OF_SOF:
-
-            reader->posCount++;
-
-            if (bit == false) { // detected a falling edge
-
-                if (reader->posCount < 20) {         // falling edge too early (nominally expected at 21 earliest)
+            if (!bit) { // detected a falling edge
+                if (reader->posCount < 14) {         // falling edge too early (nominally expected at 16 earliest)
                     DecodeReaderReset(reader);
-                } else if (reader->posCount < 23) {  // SOF for 1 out of 4 coding
+                } else if (reader->posCount <= 18) {  // SOF for 1 out of 4 coding
                     reader->Coding = CODING_1_OUT_OF_4;
                     reader->state = STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF;
-                } else if (reader->posCount < 28) {  // falling edge too early (nominally expected at 29 latest)
+                    reader->posCount = 1;
+                } else if (reader->posCount < 22) {  // falling edge too early (nominally expected at 24 latest)
                     DecodeReaderReset(reader);
-                } else {                                   // SOF for 1 out of 256 coding
+                } else {                             // SOF for 1 out of 256 coding
                     reader->Coding = CODING_1_OUT_OF_256;
                     reader->state = STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF;
+                    reader->posCount = 1;
                 }
-
             } else {
-                if (reader->posCount > 29) { // stayed high for too long
+                reader->posCount++;
+                if (reader->posCount > 26) { // stayed high for too long
                     reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
                 } else {
                     // do nothing, keep waiting
@@ -1245,60 +1242,42 @@ static int RAMFUNC Handle15693SampleFromReader(bool bit, DecodeReader_t *reader)
             break;
 
         case STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF:
-
-            reader->posCount++;
-
             if (bit) { // detected rising edge
-                if (reader->Coding == CODING_1_OUT_OF_256) {
-                    if (reader->posCount < 32) { // rising edge too early (nominally expected at 33)
-                        reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
-                    } else {
-                        reader->posCount = 1;
-                        reader->bitCount = 0;
+                if (reader->posCount < 2) { // rising edge too early (nominally expected at 8)
+                    reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                } else {
+                    reader->posCount = 1;
+                    if (reader->Coding == CODING_1_OUT_OF_256) {
+                        reader->bitCount = 1;
                         reader->byteCount = 0;
                         reader->sum1 = 1;
-                        reader->state = STATE_READER_RECEIVE_DATA_1_OUT_OF_256;
                         LED_B_ON();
-                    }
-                } else { // CODING_1_OUT_OF_4
-                    if (reader->posCount < 24) { // rising edge too early (nominally expected at 25)
-                        reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
-                    } else {
-                        reader->posCount = 1;
+                        reader->state = STATE_READER_RECEIVE_DATA_1_OUT_OF_256;
+                    } else { // CODING_1_OUT_OF_4
                         reader->state = STATE_READER_AWAIT_END_OF_SOF_1_OUT_OF_4;
                     }
                 }
             } else {
-                if (reader->Coding == CODING_1_OUT_OF_256) {
-                    if (reader->posCount > 34) { // signal stayed low for too long
-                        DecodeReaderReset(reader);
-                    } else {
-                        // do nothing, keep waiting
-                    }
-                } else { // CODING_1_OUT_OF_4
-                    if (reader->posCount > 26) { // signal stayed low for too long
-                        DecodeReaderReset(reader);
-                    } else {
-                        // do nothing, keep waiting
-                    }
+                reader->posCount++;
+                if (reader->posCount > 6) { // signal stayed low for too long
+                    DecodeReaderReset(reader);
+                } else {
+                    // do nothing, keep waiting
                 }
             }
             break;
 
         case STATE_READER_AWAIT_END_OF_SOF_1_OUT_OF_4:
-
-            reader->posCount++;
-
             if (bit) {
-                if (reader->posCount == 9) {
-                    reader->posCount = 1;
+                reader->posCount++;
+
+                if (reader->posCount == 8) {
+                    reader->posCount = 0;
                     reader->bitCount = 0;
                     reader->byteCount = 0;
-                    reader->sum1 = 1;
+                    reader->sum1 = 0;
                     reader->state = STATE_READER_RECEIVE_DATA_1_OUT_OF_4;
                     LED_B_ON();
-                } else {
-                    // do nothing, keep waiting
                 }
             } else { // unexpected falling edge
                 DecodeReaderReset(reader);
@@ -1306,62 +1285,103 @@ static int RAMFUNC Handle15693SampleFromReader(bool bit, DecodeReader_t *reader)
             break;
 
         case STATE_READER_RECEIVE_DATA_1_OUT_OF_4:
-
-            reader->posCount++;
-
-            if (reader->posCount == 1) {
-
-                reader->sum1 = bit ? 1 : 0;
-
-            } else if (reader->posCount <= 4) {
-
-                if (bit)
-                    reader->sum1++;
-
-            } else if (reader->posCount == 5) {
-
-                reader->sum2 = bit ? 1 : 0;
-
-            } else {
-                if (bit)
-                    reader->sum2++;
-            }
-
-            if (reader->posCount == 8) {
-                reader->posCount = 0;
-                if (reader->sum1 <= 1 && reader->sum2 >= 3) { // EOF
-                    LED_B_OFF(); // Finished receiving
-                    DecodeReaderReset(reader);
-                    if (reader->byteCount != 0) {
-                        return true;
-                    }
-
-                } else if (reader->sum1 >= 3 && reader->sum2 <= 1) { // detected a 2bit position
-                    reader->shiftReg >>= 2;
-                    reader->shiftReg |= (reader->bitCount << 6);
-                }
-
-                if (reader->bitCount == 15) { // we have a full byte
-
-                    reader->output[reader->byteCount++] = reader->shiftReg;
-                    if (reader->byteCount > reader->byteCountMax) {
-                        // buffer overflow, give up
-                        LED_B_OFF();
+            if (!bit) {
+                reader->sum1++;
+                if (reader->sum1 == 1) { // first low bit
+                    if (reader->posCount <= 6) { // bits : 00
+                        reader->shiftReg >>= 2;
+                        //reader->shiftReg |= (0 << 6);
+                        reader->bitCount += 2;
+                        reader->posCount = -28;
+                    } else if (reader->posCount <= 9) { // EOF
+                        LED_B_OFF(); // Finished receiving
                         DecodeReaderReset(reader);
+                        if (reader->byteCount > 0) {
+                            return true;
+                        }
+                    } else if (reader->posCount <= 14) { // bits : 01
+                        reader->shiftReg >>= 2;
+                        reader->shiftReg |= (1 << 6);
+                        reader->bitCount += 2;
+                        reader->posCount = -20;
+                    } else if (reader->posCount < 18) { // unexpected falling edge
+                        DecodeReaderReset(reader);
+                        if (reader->byteCount >= 0) {
+                            reader->output[reader->byteCount++] = reader->posCount;
+                            reader->output[reader->byteCount++] = reader->bitCount;
+                            reader->output[reader->byteCount++] = 0x42;
+                            return true;
+                        }
+                    } else if (reader->posCount <= 22) { // bits : 10
+                        reader->shiftReg >>= 2;
+                        reader->shiftReg |= (2 << 6);
+                        reader->bitCount += 2;
+                        reader->posCount = -12;
+                    } else if (reader->posCount < 26) { // unexpected falling edge
+                        DecodeReaderReset(reader);
+                        if (reader->byteCount >= 0) {
+                            reader->output[reader->byteCount++] = reader->posCount;
+                            reader->output[reader->byteCount++] = reader->bitCount;
+                            reader->output[reader->byteCount++] = 0x43;
+                            return true;
+                        }
+                    } else { // bits : 11
+                        reader->shiftReg >>= 2;
+                        reader->shiftReg |= (3 << 6);
+                        reader->bitCount += 2;
+                        reader->posCount = -4;
                     }
 
-                    reader->bitCount = 0;
-                    reader->shiftReg = 0;
-                    if (reader->byteCount == reader->jam_search_len) {
-                        if (!memcmp(reader->output, reader->jam_search_string, reader->jam_search_len)) {
-                            LED_D_ON();
-                            FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_MODE_SEND_JAM);
-                            reader->state = STATE_READER_RECEIVE_JAMMING;
+                    if (reader->bitCount == 8)
+                    {
+                        reader->output[reader->byteCount++] = reader->shiftReg;
+                        if (reader->byteCount > reader->byteCountMax) {
+                            // buffer overflow, give up
+                            LED_B_OFF();
+                            DecodeReaderReset(reader);
+                        }
+
+                        reader->bitCount = 0;
+                        reader->shiftReg = 0;
+                        if (reader->byteCount == reader->jam_search_len) {
+                          if (!memcmp(reader->output, reader->jam_search_string, reader->jam_search_len)) {
+                          LED_D_ON();
+                          FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_MODE_SEND_JAM);
+                          reader->state = STATE_READER_RECEIVE_JAMMING;
+                          }
                         }
                     }
-
-                } else {
-                    reader->bitCount++;
+                } else if (reader->sum1 > 6) { // too long low bit
+                    DecodeReaderReset(reader);
+                    if (reader->byteCount >= 0) {
+                        reader->output[reader->byteCount++] = reader->posCount;
+                        reader->output[reader->byteCount++] = reader->bitCount;
+                        reader->output[reader->byteCount++] = 0x44;
+                        return true;
+                    }
+                }
+            } else {
+                reader->posCount++;
+                if (reader->posCount > 30) {
+                    reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                    if (reader->byteCount >= 0) {
+                        reader->output[reader->byteCount++] = reader->posCount;
+                        reader->output[reader->byteCount++] = reader->bitCount;
+                        reader->output[reader->byteCount++] = 0x45;
+                        return true;
+                    }
+                }
+                if (reader->sum1 == 1) {
+                    reader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                    if (reader->byteCount >= 0) {
+                        reader->output[reader->byteCount++] = reader->posCount;
+                        reader->output[reader->byteCount++] = reader->bitCount;
+                        reader->output[reader->byteCount++] = 0x46;
+                        return true;
+                    }
+                } else if (reader->sum1 > 1) {
+                    reader->posCount += reader->sum1;
+                    reader->sum1 = 0;
                 }
             }
             break;
diff --git a/fpga/hi_reader.v b/fpga/hi_reader.v
index 1a0b375d3..07afdc2de 100644
--- a/fpga/hi_reader.v
+++ b/fpga/hi_reader.v
@@ -44,8 +44,13 @@ reg after_hysteresis, after_hysteresis_prev, after_hysteresis_prev_prev;
 reg [11:0] has_been_low_for;
 always @(negedge adc_clk)
 begin
+`ifdef WITH_HF_15_LOWSIGNAL
+    if (& adc_d[7:4]) after_hysteresis <= 1'b1;
+    else if (~(| adc_d[7:6])) after_hysteresis <= 1'b0;
+`else
     if (& adc_d[7:0]) after_hysteresis <= 1'b1;
     else if (~(| adc_d[7:0])) after_hysteresis <= 1'b0;
+`endif
 
     if (after_hysteresis)
     begin