diff --git a/Makefile b/Makefile
index 8fabffa..0a0b035 100644
--- a/Makefile
+++ b/Makefile
@@ -78,6 +78,11 @@ distclean: clean
 	$(E) "[REM] $(BINDIR)"
 	$(Q) $(RMR) $(BINDIR)
 
+.PHONY: listen
+listen: ./opt/tools/serial-listen.py
+	$(E) "[PY3] $<"
+	$(Q) ./$<
+
 $(TMPDIRS):
 	$(E) "[DIR] $@"
 	$(Q) $(MKDIR) $@
diff --git a/docs/AHT20.pdf b/docs/AHT20.pdf
index 166796f..382da12 100755
Binary files a/docs/AHT20.pdf and b/docs/AHT20.pdf differ
diff --git a/src/bus/twi.c b/src/bus/twi.c
index fb94790..910b738 100644
--- a/src/bus/twi.c
+++ b/src/bus/twi.c
@@ -77,6 +77,35 @@ int TWI_Write(unsigned char data)
 	return 0;
 }
 
+unsigned char TWI_Read_ACK(void)
+{
+	// Read data and acknowledge
+
+	TWCR = (1 << TWEN)   // Enable TWI
+	     | (1 << TWINT)  // Clear interrupt flag
+	     | (1 << TWEA);  // Send acknowledgment
+
+	// Wait until data read
+
+	while ((TWCR & (1 << TWINT)) == 0);
+
+	return TWDR;
+}
+
+unsigned char TWI_Read_NACK(void)
+{
+	// Read data, expect last byte
+
+	TWCR = (1 << TWEN)    // Enable TWI
+	     | (1 << TWINT);  // Clear interrupt flag
+
+	// Wait until data read
+
+	while ((TWCR & (1 << TWINT)) == 0);
+
+	return TWDR;
+}
+
 int TWI_Wait_ACK(void)
 {
 	unsigned int status;
diff --git a/src/bus/twi.h b/src/bus/twi.h
index a43a44b..c20ca9a 100644
--- a/src/bus/twi.h
+++ b/src/bus/twi.h
@@ -10,6 +10,8 @@ int TWI_Init(void);
 int TWI_Start(unsigned char addr, unsigned char mode);
 int TWI_SetChannel(int channel);
 int TWI_Write(unsigned char data);
+unsigned char TWI_Read_ACK(void);
+unsigned char TWI_Read_NACK(void);
 int TWI_Wait_ACK(void);
 int TWI_Stop(void);
 
diff --git a/src/main.c b/src/main.c
index 8d6ffb5..9689d00 100644
--- a/src/main.c
+++ b/src/main.c
@@ -6,6 +6,136 @@
 
 #include <avr/interrupt.h>
 
+short TWI_ReadAHT20(void)
+{
+	unsigned char data, crc;
+
+	// After the transmission is initiated, the first
+	// byte of the subsequent I2C transmission includes
+	// the 7-bit I2C device address 0x38 and a SDA
+	// direction bit.
+
+	// Soft reset device.
+
+	TWI_Start(0x38, 0);
+	TWI_Write(0xBA);
+	TWI_Wait_ACK();
+	TWI_Stop();
+
+	// Wait 40ms after power-on.
+
+	Sleep(40);
+
+	// Before reading the temperature and humidity
+	// values, first check whether the calibration
+	// enable bit Bit [3] of the status word is 1 (you
+	// can get a byte of status word by sending 0x71).
+
+	TWI_Start(0x38, 0);
+	TWI_Write(0x71);
+	TWI_Wait_ACK();
+
+	data = TWI_Read_NACK();
+	TWI_Stop();
+
+	Info("Received calibration status %02X.", data);
+
+	// If not 1, need to send 0xBE command (for
+	// initialization), this command parameter has two
+	// bytes, the first byte is 0x08, the second byte
+	// is 0x00, and then wait for 10ms.
+
+	if (data & ~BIT(3)) {
+		Info("Requesting calibration...");
+
+		TWI_Start(0x38, 0);
+		TWI_Write(0xBE);
+		TWI_Wait_ACK();
+		TWI_Write(0x08);
+		TWI_Wait_ACK();
+		TWI_Write(0x00);
+		TWI_Wait_ACK();
+
+		Sleep(10);
+		data = TWI_Read_NACK();
+		TWI_Stop();
+
+		if (data & ~BIT(3)) {
+			Info("Error: Calibration failed.");
+			return -1;
+		}
+	}
+
+	// Send the 0xAC command directly (trigger
+	// measurement). The parameter of this command has
+	// two bytes, the first byte is 0x33 and the second
+	// byte is 0x00.
+
+	Info("Triggering measurement...");
+
+	TWI_Start(0x38, 0);
+	TWI_Wait_ACK();
+	TWI_Write(0xAC);
+	TWI_Wait_ACK();
+	TWI_Write(0x33);
+	TWI_Wait_ACK();
+	TWI_Write(0x00);
+	TWI_Wait_ACK();
+	TWI_Stop();
+
+	// Wait for 80ms to wait for the measurement to be
+	// completed. If the read status word Bit [7] is 0,
+	// it indicates that the measurement is completed,
+	// and six bytes can be read in a row. Otherwise
+	// continue to wait.
+
+	Info("Reading measurement...");
+
+	TWI_Start(0x38, 1); // Read
+	TWI_Wait_ACK();
+
+	do {
+		Sleep(80);
+		data = TWI_Read_ACK();
+	} while (data & BIT(7));
+
+	data = TWI_Read_ACK();
+	Info("Received data byte %02X.", data);
+	data = TWI_Read_ACK();
+	Info("Received data byte %02X.", data);
+	data = TWI_Read_ACK();
+	Info("Received data byte %02X.", data);
+	data = TWI_Read_ACK();
+	Info("Received data byte %02X.", data);
+	data = TWI_Read_ACK();
+	Info("Received data byte %02X.", data);
+	data = TWI_Read_ACK();
+	Info("Received data byte %02X.", data);
+
+	// After receiving six bytes, the next byte is the
+	// CRC check data, the user can read it as needed,
+	// if the receiving end needs CRC check, then send
+	// it after receiving the sixth byte ACK response,
+	// otherwise NACK is sent out, CRC initial value is
+	// 0xFF. The CRC8 check polynomial is:
+	// CRC[7:0]= 1 + (x^4) + (x^5) + (x^8)
+
+	crc = TWI_Read_NACK();
+	Info("Received CRC8 byte %02X.", crc);
+
+	// Calculate the temperature and humidity values.
+	// Note: The calibration status check in the first
+	// step only needs to be checked at power-on. No
+	// operation is required during the normal
+	// acquisition process.
+
+	// TODO: Calculate values
+
+	TWI_Stop();
+
+	return 0;
+}
+
 int main(void)
 {
 	USART_Init();
@@ -27,7 +157,14 @@ int main(void)
 	// TODO: Set FAN03 timer frequency
 	// TODO: Implement ADS1115 and AHT20
 
+	// TEM01, TEM02, TEM03
+	// HUM01, HUM02, HUM03
+
+	// TWI_GetValue(TEM03)
+	// TWI_GetValue(HUM03)
+
 	TWI_SetChannel(AHT01); // I2C Mux
+	TWI_ReadAHT20(); // TEMP and RH
 
 	Info("Running idle loop...");