diff --git a/driver/drv/b15f.cpp b/driver/drv/b15f.cpp
index fc3f804..18cc93b 100644
--- a/driver/drv/b15f.cpp
+++ b/driver/drv/b15f.cpp
@@ -28,11 +28,12 @@ void B15F::init()
 	
 	
 	 // Temporärer Test
-	uint8_t block[] = {0, 1, 2, 3};
+	uint8_t block[16];
 	while(1)
 	{
 		usart.writeBlock(&block[0], 0, sizeof(block));
 		usart.printStatistics();
+		usleep(1000);
 	}
 	throw std::runtime_error("SCHLUSS");
 	
diff --git a/driver/drv/b15f.o b/driver/drv/b15f.o
index 79f3e7b..bffe005 100644
Binary files a/driver/drv/b15f.o and b/driver/drv/b15f.o differ
diff --git a/driver/drv/usart.cpp b/driver/drv/usart.cpp
index 1516c59..93362ff 100644
--- a/driver/drv/usart.cpp
+++ b/driver/drv/usart.cpp
@@ -2,7 +2,7 @@
 
 void USART::openDevice(std::string device)
 {
-	file_desc = open(device.c_str(), O_RDWR | O_NOCTTY | O_NDELAY);
+	file_desc = open(device.c_str(), O_RDWR | O_NOCTTY | O_NDELAY /* | O_NONBLOCK*/);
 	if(file_desc <= 0)
 		throw USARTException("Fehler beim Öffnen des Gerätes");
 	
@@ -96,7 +96,7 @@ int USART::read_timeout(uint8_t* buffer, uint16_t offset, uint8_t len, uint32_t
 		elapsed = std::chrono::duration_cast<std::chrono::microseconds>(end - start).count();
 	}
 	
-	return n_read;
+	return 0;
 }
 
 int USART::write_timeout(uint8_t* buffer, uint16_t offset, uint8_t len, uint32_t timeout)
@@ -150,23 +150,35 @@ void USART::writeBlock(uint8_t* buffer, uint16_t offset, uint8_t len)
 		block_buffer[len + 2] = BLOCK_END;
 			
 		// send block
+		clearOutputBuffer();
+		clearInputBuffer();
 		int n_sent = write_timeout(&block_buffer[0], 0, len + 3, us_per_bit * n_total);
 		if(n_sent != n_total)
 			throw std::runtime_error("fatal (send): " + std::to_string(n_sent));
+		
+		/*for(uint8_t i = 0; i < len + 3; i++)
+		{
+			write_timeout(&block_buffer[i], 0, 1, us_per_bit * n_total);
+			//tcdrain(file_desc);
+			//usleep(1000);
+		}*/
 			
 		// flush output data
 		tcdrain(file_desc);
 		
-		usleep(us_per_bit * n_total);
+		//usleep(us_per_bit * n_total * 10);
 			
 		// check response
-		int n_read = read_timeout(&aw, 0, 1, us_per_bit);
+		int n_read = read_timeout(&aw, 0, 1, us_per_bit * n_blocks_total * 10);
 		for(uint16_t i = 0; i < 255 && n_read != 1; i++)
 		{
 			writeByte(0x80); // Stoppzeichen für Block
-			tcdrain(file_desc);
+			if(tcdrain(file_desc))
+			{
+				std::cout << "drain failed" << std::endl;
+			}
 			std::cout << "WARNING: read error (" << n_read << "), retry #" << (int) i << std::endl;
-			usleep(us_per_bit);
+			usleep(us_per_bit*100);
 			n_read = read_timeout(&aw, 0, 1, us_per_bit);
 		}
 		
diff --git a/driver/drv/usart.h b/driver/drv/usart.h
index e375e8c..1659316 100644
--- a/driver/drv/usart.h
+++ b/driver/drv/usart.h
@@ -125,7 +125,7 @@ public:
 	/***************************************/
 	
 	constexpr static uint8_t CRC7_POLY = 0x91;
-	constexpr static uint8_t MAX_BLOCK_SIZE = 16;
+	constexpr static uint8_t MAX_BLOCK_SIZE = 64;
 	constexpr static uint8_t BLOCK_END = 0x80;
 private:
 	
diff --git a/driver/drv/usart.o b/driver/drv/usart.o
index ed30f7a..a00541e 100644
Binary files a/driver/drv/usart.o and b/driver/drv/usart.o differ
diff --git a/driver/main b/driver/main
index 307f0d1..1fb9afc 100755
Binary files a/driver/main and b/driver/main differ
diff --git a/firmware/B15F.elf b/firmware/B15F.elf
index c37872f..c153cbd 100644
Binary files a/firmware/B15F.elf and b/firmware/B15F.elf differ
diff --git a/firmware/B15F.hex b/firmware/B15F.hex
index 507edfe..582abad 100644
--- a/firmware/B15F.hex
+++ b/firmware/B15F.hex
@@ -3,190 +3,235 @@
 :100020000C947D000C947D000C947D000C947D005C
 :100030000C947D000C947D000C947D000C947D004C
 :100040000C947D000C947D000C947D000C947D003C
-:100050000C947D000C947D000C947D000C947D002C
+:100050000C947F000C947D000C947D000C947D002A
 :100060000C947D000C947D000C947D000C947D001C
 :100070000C947D000C947D000C947D000C947D000C
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+:1000A00020013E010D0711241FBECFEFD0E4DEBFBB
+:1000B000CDBF11E0A0E0B1E0ECE8FEE000E00BBF56
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+:1005F00087E893E10197F1F700C000002196C1154B
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+:100D00002304682F89E691E00E948302BC0182E2FD
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+:100D300091E00E942304882E82E291E00E94230425
+:100D4000982E82E291E00E942A04EC0182E291E076
+:100D50000E942A045C0182E291E00E942A048C0134
+:100D60006FEF82E291E00E949103A09E6001A19E3C
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+:100D90000E9483027C01692D89E691E00E94830212
+:100DA0008C01B70182E291E00E949803B80182E2CF
+:100DB00091E00E949803CA0DDB1DCC15DD05FCF205
+:100DC0006FEF82E291E0DF91CF911F910F91FF9041
+:100DD000EF90DF90CF90BF90AF909F908F900C944A
+:100DE00091030E94B6006FEF86E791E00E94C70171
+:100DF0002FE78AE196E0215080409040E1F700C063
+:100E0000000060E086E791E00E94C70187E893E177
+:100E10000197F1F700C00000F9CF89E791E00E9447
+:100E2000410142E069E771E086E791E00E948001BC
+:100E300043E069E771E083E791E00E94800145E0CB
+:100E400069E771E080E791E00E94800140E069E796
+:100E500071E08DE691E00E944F0241E069E771E0A8
+:100E60008AE691E00E944F021092220110926801DE
+:100E7000109267010895EE0FFF1F0024001C0BBEA7
+:0C0E80000790F691E02D0994F894FFCF44
+:100E8C00626F617264696E666F2E680031303A343D
+:100E9C00333A3130004170722020322032303139F7
+:020EAC00000044
 :00000001FF
diff --git a/firmware/global_vars.cpp b/firmware/global_vars.cpp
index 35b855c..88e73ca 100644
--- a/firmware/global_vars.cpp
+++ b/firmware/global_vars.cpp
@@ -1,11 +1,11 @@
 #include "global_vars.h"
 
-SPI spi;
-MCP23S17 beba0(spi, SPIADR::BEBA0);
-MCP23S17 beba1(spi, SPIADR::BEBA1);
-MCP23S17 sw(spi, SPIADR::SWITCH);
-TLC5615 dac0(spi, SPIADR::AA0);
-TLC5615 dac1(spi, SPIADR::AA1);
-ADU adu;
-USART usart;
+volatile SPI spi;
+volatile MCP23S17 beba0(*((SPI*) &spi), SPIADR::BEBA0);
+volatile MCP23S17 beba1(*((SPI*) &spi), SPIADR::BEBA1);
+volatile MCP23S17 sw(*((SPI*) &spi), SPIADR::SWITCH);
+volatile TLC5615 dac0(*((SPI*) &spi), SPIADR::AA0);
+volatile TLC5615 dac1(*((SPI*) &spi), SPIADR::AA1);
+volatile ADU adu;
+volatile USART usart;
 
diff --git a/firmware/global_vars.h b/firmware/global_vars.h
index c7ecd0c..94511ec 100644
--- a/firmware/global_vars.h
+++ b/firmware/global_vars.h
@@ -6,13 +6,13 @@
 #include "adu.h"
 #include "usart.h"
 
-extern SPI spi;
-extern MCP23S17 beba0;
-extern MCP23S17 beba1;
-extern MCP23S17 sw;
-extern TLC5615 dac0;
-extern TLC5615 dac1;
-extern ADU adu;
-extern USART usart;
+extern volatile SPI spi;
+extern volatile MCP23S17 beba0;
+extern volatile MCP23S17 beba1;
+extern volatile MCP23S17 sw;
+extern volatile TLC5615 dac0;
+extern volatile TLC5615 dac1;
+extern volatile ADU adu;
+extern volatile USART usart;
 
 #endif // GLOBAL_VARS_H
diff --git a/firmware/main.cpp b/firmware/main.cpp
index a1eb489..a243042 100644
--- a/firmware/main.cpp
+++ b/firmware/main.cpp
@@ -9,18 +9,29 @@
 
 #define WDT_TIMEOUT WDTO_15MS
 
+ISR(USART0_RX_vect)
+{
+	if(UCSR0A & _BV(DOR0))
+	{
+		((MCP23S17*) &beba0)->writePortA(0xFF);
+	}
+	cli();
+	((USART*) &usart)->nextByte(UDR0);
+	sei();
+}
+
 void initAll()
 {
-	spi.init();
+	((SPI*) &spi)->init();
 
-	beba0.setDirA(0x00); // alle Ausgang
-	beba0.setDirB(0xFF); // alle Eingang
-	beba1.setDirA(0x00); // alle Ausgang
-	beba1.setDirB(0xFF); // alle Eingang
-	sw.setDirB(0xFF); // alle Eingang
+	((MCP23S17*) &beba0)->setDirA(0x00); // alle Ausgang
+	((MCP23S17*) &beba0)->setDirB(0xFF); // alle Eingang
+	((MCP23S17*) &beba1)->setDirA(0x00); // alle Ausgang
+	((MCP23S17*) &beba1)->setDirB(0xFF); // alle Eingang
+	((MCP23S17*) &sw)->setDirB(0xFF); // alle Eingang
 
-	adu.init();
-	usart.init();
+	((ADU*) &adu)->init();
+	((USART*) &usart)->init();
 
 	// aktiviere Interrupts
 	sei();
@@ -35,9 +46,9 @@ void handleRequest()
 {	
 	wdt_disable();
 
-	beba1.writePortA(0xFF);
-	const uint8_t req = usart.readByte();
-	beba1.writePortA(0x00);
+	((MCP23S17*) &beba1)->writePortA(0xFF);
+	const uint8_t req = ((USART*) &usart)->readByte();
+	((MCP23S17*) &beba1)->writePortA(0x00);
 
 	// starte WDT
 	wdt_enable(WDT_TIMEOUT);
@@ -104,16 +115,16 @@ int main()
 
 	
 	// Reset anzeigen
-	beba0.writePortA(0xFF);
+	((MCP23S17*) &beba0)->writePortA(0xFF);
 	_delay_ms(100);
-	beba0.writePortA(0x00);
+	((MCP23S17*) &beba0)->writePortA(0x00);
 
 	uint8_t n = 0;
 	uint8_t block[16];
 	while(1)
 	{
-		beba0.writePortA(n++ & 0xFF);
-		usart.readBlock(&block[0], 0);
+		//testAll();
+		_delay_ms(1);
 	}
 
 	while(1)
diff --git a/firmware/requests.cpp b/firmware/requests.cpp
index 3ab761b..4d870e7 100644
--- a/firmware/requests.cpp
+++ b/firmware/requests.cpp
@@ -2,99 +2,99 @@
 
 void rqTestConnection()
 {
-	uint8_t dummy = usart.readByte();
-	usart.writeByte(USART::MSG_OK);
-	usart.writeByte(dummy);
+	uint8_t dummy = ((USART*) &usart)->readByte();
+	((USART*) &usart)->writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(dummy);
 }
 
 void rqBoardInfo()
 {
-	usart.writeByte(3); // Anzahl an Strings
+	((USART*) &usart)->writeByte(3); // Anzahl an Strings
 	
-	usart.writeStr(DATE, sizeof(DATE));
-	usart.writeStr(TIME, sizeof(TIME));
-	usart.writeStr(FSRC, sizeof(FSRC));
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeStr(DATE, sizeof(DATE));
+	((USART*) &usart)->writeStr(TIME, sizeof(TIME));
+	((USART*) &usart)->writeStr(FSRC, sizeof(FSRC));
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 }
 
 void rqTestIntConv()
 {
-	usart.writeInt(usart.readInt() * 3);
+	((USART*) &usart)->writeInt(((USART*) &usart)->readInt() * 3);
 }
 
 void rqDigitalWrite0()
 {
-	uint8_t port = usart.readByte();
-	beba0.writePortA(port);
+	uint8_t port = ((USART*) &usart)->readByte();
+	((MCP23S17*) &beba0)->writePortA(port);
 
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 }
 
 void rqDigitalWrite1()
 {
-	uint8_t port = usart.readByte();
-	beba1.writePortA(port);
+	uint8_t port = ((USART*) &usart)->readByte();
+	((MCP23S17*) &beba1)->writePortA(port);
 
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 }
 
 void rqDigitalRead0()
 {
-	uint8_t port = beba0.readPortB();
-	usart.writeByte(port);
+	uint8_t port = ((MCP23S17*) &beba0)->readPortB();
+	((USART*) &usart)->writeByte(port);
 }
 
 void rqDigitalRead1()
 {
-	uint8_t port = beba1.readPortB();
-	usart.writeByte(port);
+	uint8_t port = ((MCP23S17*) &beba1)->readPortB();
+	((USART*) &usart)->writeByte(port);
 }
 
 void rqAnalogWrite0()
 {
-	uint16_t value = usart.readInt();
-	dac0.setValue(value);
+	uint16_t value = ((USART*) &usart)->readInt();
+	((TLC5615*) &dac0)->setValue(value);
 
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 }
 
 void rqAnalogWrite1()
 {
-	uint16_t value = usart.readInt();
-	dac1.setValue(value);
+	uint16_t value = ((USART*) &usart)->readInt();
+	((TLC5615*) &dac1)->setValue(value);
 
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 }
 
 void rqAnalogRead()
 {
-	uint8_t channel = usart.readByte();
-	uint16_t value = adu.getValue(channel);
-	usart.writeInt(value);
+	uint8_t channel = ((USART*) &usart)->readByte();
+	uint16_t value = ((ADU*) &adu)->getValue(channel);
+	((USART*) &usart)->writeInt(value);
 }
 
 void rqAdcDacStroke()
 {	
-	uint8_t channel_a = usart.readByte();
-	uint8_t channel_b = usart.readByte();
+	uint8_t channel_a = ((USART*) &usart)->readByte();
+	uint8_t channel_b = ((USART*) &usart)->readByte();
 	
-	int16_t start = static_cast<int16_t>(usart.readInt());
-	int16_t delta = static_cast<int16_t>(usart.readInt());
-	int16_t count = static_cast<int16_t>(usart.readInt());
+	int16_t start = static_cast<int16_t>(((USART*) &usart)->readInt());
+	int16_t delta = static_cast<int16_t>(((USART*) &usart)->readInt());
+	int16_t count = static_cast<int16_t>(((USART*) &usart)->readInt());
 
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 	
 	count *= delta;
 	
 	for(int16_t i = start; i < count; i += delta)
 	{
-		dac0.setValue(i);
+		((TLC5615*) &dac0)->setValue(i);
 		wdt_reset();
 
-		uint16_t val_a = adu.getValue(channel_a);
-		uint16_t val_b = adu.getValue(channel_b);
-		usart.writeInt(val_a);
-		usart.writeInt(val_b);
+		uint16_t val_a = ((ADU*) &adu)->getValue(channel_a);
+		uint16_t val_b = ((ADU*) &adu)->getValue(channel_b);
+		((USART*) &usart)->writeInt(val_a);
+		((USART*) &usart)->writeInt(val_b);
 
 		/*union doubleword
 		{
@@ -103,19 +103,19 @@ void rqAdcDacStroke()
 		};
 
 		union doubleword dw;
-		dw.word[0] = adu.getValue(channel_a);
-		dw.word[1] = adu.getValue(channel_b);
+		dw.word[0] = ((ADU*) &adu)->getValue(channel_a);
+		dw.word[1] = ((ADU*) &adu)->getValue(channel_b);
 		
 		uint8_t ret = 0;
 		do
 		{
 			wdt_reset();
-			ret = usart.writeBlock(&(dw.byte[0]), 4);
+			ret = ((USART*) &usart)->writeBlock(&(dw.byte[0]), 4);
 
 			if(ret == 0)
 				return;
 		} while(ret != USART::MSG_OK);*/
 	}
 	
-	usart.writeByte(USART::MSG_OK);
+	((USART*) &usart)->writeByte(USART::MSG_OK);
 }
diff --git a/firmware/selftest.cpp b/firmware/selftest.cpp
index 2cf7bd2..c75a77d 100644
--- a/firmware/selftest.cpp
+++ b/firmware/selftest.cpp
@@ -13,7 +13,7 @@ void testBEBA0(void)
 {
 	for(uint8_t i = 0; i < 9; i++)
 	{
-		beba0.writePortA(_BV(i));
+		((MCP23S17*) &beba0)->writePortA(_BV(i));
 
 		if(i < 8)
 			_delay_ms(200);
@@ -24,7 +24,7 @@ void testBEBA1(void)
 {
 	for(uint8_t i = 0; i < 9; i++)
 	{
-		beba1.writePortA(_BV(i));
+		((MCP23S17*) &beba1)->writePortA(_BV(i));
 		
 		if(i < 8)
 			_delay_ms(200);
@@ -35,22 +35,22 @@ void testDAC0(void)
 {
 	for(uint16_t i = 0; i < 1024; i++)
 	{
-		dac0.setValue(i);
+		((TLC5615*) &dac0)->setValue(i);
 		_delay_ms(1);
 	}
 	_delay_ms(100);
-	dac0.setValue(0);
+	((TLC5615*) &dac0)->setValue(0);
 }
 
 void testDAC1(void)
 {
 	for(uint16_t i = 0; i < 1024; i++)
 	{
-		dac1.setValue(i);
+		((TLC5615*) &dac1)->setValue(i);
 		_delay_ms(1);
 	}
 	_delay_ms(100);
-	dac1.setValue(0);
+	((TLC5615*) &dac1)->setValue(0);
 }
 
 void testMirror()
@@ -61,9 +61,9 @@ void testMirror()
 	// Endlosschleife
 	while(1)
 	{
-		dac0.setValue(adu.getValue(0));
-		dac1.setValue(adu.getValue(1));
-		beba0.writePortA(beba0.readPortB());
-		beba1.writePortA(sw.readPortB());
+		((TLC5615*) &dac0)->setValue(((ADU*) &adu)->getValue(0));
+		((TLC5615*) &dac1)->setValue(((ADU*) &adu)->getValue(1));
+		((MCP23S17*) &beba0)->writePortA(((MCP23S17*) &beba0)->readPortB());
+		((MCP23S17*) &beba1)->writePortA(((MCP23S17*) &sw)->readPortB());
 	}
 }
diff --git a/firmware/usart.cpp b/firmware/usart.cpp
index d03149d..dc78264 100644
--- a/firmware/usart.cpp
+++ b/firmware/usart.cpp
@@ -4,7 +4,7 @@ void USART::init()
 {
 	UCSR0A = _BV(U2X0);
 	
-	UCSR0B = _BV(RXEN0) | _BV(TXEN0);
+	UCSR0B = _BV(RXEN0) | _BV(TXEN0) | _BV(RXCIE0);
 
 	// Einstellen des Datenformats: 8 Datenbits, 1 Stoppbit
 	UCSR0C = _BV(UCSZ00) |_BV(UCSZ01);// (1<<URSEL0)|(1<<UCSZ10)|(1<<UCSZ00);
@@ -15,7 +15,7 @@ void USART::init()
 
 }
 
-void USART::flush()
+void USART::clearInputBuffer()
 {
 	uint8_t dummy;
 	do
@@ -94,6 +94,79 @@ uint16_t USART::readInt()
 	return v;
 }
 
+void USART::nextByte(uint8_t byte)
+{
+	switch(seq)
+	{
+		case IDLE:
+		{
+			if(byte > MAX_BLOCK_SIZE)
+			{
+				clearInputBuffer();
+				writeByte(MSG_FAIL);
+				seq = BlockSequence::IDLE;
+			}
+			else
+			{
+				block_buffer[0] = byte;
+				crc = 0;
+				block_pos = 0;
+				seq = BlockSequence::LEN;
+			}
+			break;
+		}
+		case LEN:
+		{
+			block_buffer[block_pos] = byte;
+			seq = BlockSequence::DATA;
+			break;
+		}
+		case DATA:
+		{
+			block_buffer[block_pos] = byte;
+			crc ^= byte;
+			for (uint8_t i = 0; i < 8; i++)
+			{
+				if (crc & 1)
+					crc ^= CRC7_POLY;
+				crc >>= 1;
+			}
+			if(block_pos == block_buffer[0])
+				seq = BlockSequence::CRC;
+			else if(block_pos >= block_buffer[0])
+			{
+				clearInputBuffer();
+				writeByte(MSG_FAIL);
+				seq = BlockSequence::IDLE;				
+			}
+			break;
+		}
+		case CRC:
+		{
+			block_buffer[block_pos] = byte;
+			crc ^= byte;
+			for (uint8_t i = 0; i < 8; i++)
+			{
+				if (crc & 1)
+					crc ^= CRC7_POLY;
+				crc >>= 1;
+			}
+			seq = BlockSequence::END;
+			break;
+		}
+		case END:
+		{
+			clearInputBuffer();
+			writeByte(crc == 0 ? MSG_OK : MSG_FAIL);
+			seq = BlockSequence::IDLE;
+			break;
+		}
+
+
+	}
+	block_pos++;
+}
+
 void USART::readBlock(uint8_t* ptr, uint8_t offset)
 {
 	ptr += offset;
@@ -129,7 +202,7 @@ void USART::readBlock(uint8_t* ptr, uint8_t offset)
 		}
 
 		
-		flush(); // leere Eingangspuffer
+		clearInputBuffer(); // leere Eingangspuffer
 		
 		writeByte(crc == 0 ? MSG_OK : MSG_FAIL);
 	}
diff --git a/firmware/usart.h b/firmware/usart.h
index f427f3b..ab5022e 100644
--- a/firmware/usart.h
+++ b/firmware/usart.h
@@ -5,15 +5,20 @@
 #include <util/delay.h>
 #include <stdint.h>
 
-constexpr uint32_t BAUDRATE = 115200; // 38400
-constexpr uint8_t  CRC7_POLY = 0x91;
-constexpr uint8_t MAX_BLOCK_SIZE = 16;
+enum BlockSequence
+{
+	IDLE = 0,
+	LEN  = 1,
+	DATA = 2,
+	CRC  = 3,
+	END  = 4,
+};
 
 class USART
 {
 public:
 	void init(void);
-	void flush(void);
+	void clearInputBuffer(void);
 
 	void writeByte(uint8_t);
 	void writeInt(uint16_t);
@@ -23,10 +28,24 @@ public:
 	uint8_t readByte(void);
 	uint16_t readInt(void);
 	uint32_t readLong(void);
+
+	void nextByte(uint8_t byte);
 	void readBlock(uint8_t*, uint8_t);
 
 	constexpr static uint8_t MSG_OK = 0xFF;
 	constexpr static uint8_t MSG_FAIL = 0xFE;
+
+	uint8_t block_pos = 0;
+
+	// constants
+	constexpr static uint32_t BAUDRATE       = 115200; // 38400
+	constexpr static uint8_t  CRC7_POLY      = 0x91;
+	constexpr static uint8_t  MAX_BLOCK_SIZE = 64;
+	constexpr static uint8_t  BLOCK_END      = 0x80;
+private:
+	uint8_t block_buffer[MAX_BLOCK_SIZE + 3]; // don't store BLOCK_END byte
+	uint8_t crc;
+	BlockSequence seq = BlockSequence::IDLE;
 };
 
 #endif // USART_H