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Learn about Serial communication between ESP8266 and Arduino. Transmit data between two ESP8266 and Arduino using RX/TX lines. ESP8266 Serial Communication is used to send or receive data from ESP8266 WiFi Module. Code for basic Serial communication between Arduino and NodeMCU or ESP8266 is also given.
###Objective:
- Supply power to an ESP8266 chip via USB
- Achieve serial communication between ESP8266 and computer
- Verifying connection is setup correctly
- Use and get familiar with the ESPlorer IDE
The section will show how the wiring of the ESP8266 device to a computer is done. This is required in order to:
- flash new firmware
- upload code
- power the chip when not using a battery (useful during prototype/design stage)
- helps with debugging
Most ESP8266 comes from manufacture with stock AT firmware. This section will cover how to test if the connection is done correctly by issuing an AT command.
ESP8266-01
###Technologies, Tools, and Resources used:
- A Computer
- Cables
- A 3.3V capable Serial-USB adapter
- Micro USB to USB cable
- ESPlorer IDE
ESP8266-01 Connectivity Guide
Installing drivers for serial to usb adapter
By default, certain Serial-USB adapters like the FTDI-based adapter need driver to work, thus you needs to instal the driver manually. The way of installing the driver is shown and basically is the same for the other Serial-USB adapters that may need their own driver receptively.
By default, certain Serial-USB adapters like the FTDI-based adapter need driver to work, thus you needs to instal the driver manually. The way of installing the driver is shown and basically is the same for the other Serial-USB adapters that may need their own driver receptively.
A common type uses the FTDI chipset. You can verify if you are using one by reading if 'FTDI' is printed on the board or microchip. You may find the driver for FTDI-based adapter at:http://www.ftdichip.com/Drivers/VCP.htm
Note: May need administrative privileges in order to install drivers
Note: May need administrative privileges in order to install drivers
- Download the driver for your platform. For Windows, as of 14/05/2015 the latest available version was 2.12. Run ‘CMD_v2.12.00_WHQL_Certified.exe’
- Choose ‘Extract’ and continue till the installation is finished.
- If installation was successful, green check marks should be shown and USB serial port should be ready to use when the FTDI is connected to a computers USB port.
- The FTDI drivers have been successfully installed and can be used to communication with the ESP8266 using a terminal.
- Open control panel / hardware and sound / device manager, expand the section Ports (com and lpt).
- Find USB serial port (com_) where _ is a number. Make note of this com port number. If you dot see USB serial port (com_), then verify the driver installed correctly, and that the FTDI board is plugged into the pc via micro USB.
Connection wiring between the ESP8266-01 and a serial to USB device
This section shows how to wire up the ESP8266-1 to USB device in order to be able to communicate the ESP8266 device with a terminal.
This section shows how to wire up the ESP8266-1 to USB device in order to be able to communicate the ESP8266 device with a terminal.
- Connect the RxD pin on the ESP8266-01 to the TxD on the USB to serial device.
- Connect the TxD pin on the ESP8266-01 to the RxD on the USB to serial device.
- Connect the ground pin on the ESP8266-01 to ground on the USB serial device. This can be done directly or through a common ground.
- Connect the VCC pin on the ESP8266-01 to the VCC (votage out or Voltage +) on the USB to serial device. this can be done directly or via a common power line. Ensure that the voltage is 3.3 volts!
- Connect the CH_PD pin on the ESP8266-01 to VCC or any 3.3v power source.
- Ensure that GPIO0 on the ESP8266 is not set low via a ground.
Refer to the table below for a summary
ESP8266_01 | Direct/breadboard | serial - USB | Explanation |
---|---|---|---|
RxD | Direct | TxD | Enable communications to receive and transmit data |
TxD | Direct | RxD | Enable communications to receive and transmit data |
GND | via breadboard | GND | Common ground zero voltage reference for all pins |
VCC | via breadboard | VCC | Power supply |
CH_PD | via breadboard | VCC 3.3V | To enable the chip |
Note: In order to communicate with the ESP8266, the GPIO0 pin IS NOT TO BE set low (by connecting to GND) unless wanting to enter flash mode.
Testing the Connection
1.Connect the USB cable to the serial to USB device and the computer.
2.Open the ESPlorer that is provided (via the installer). Make sure the USB cable is connected to the computer so the ESPlorer can detect which COM port is available. This should be the same as the one you noted previously in step 6 installing driver.
3.Click on the ‘open’ button to open the port and start communicating with the device. The ‘Open’ ‘DTR’ ‘RTS’ circles should display green if in the correct mode. The output may come out as ERROR if the NodeMCU or MicroPython firmware is not yet flashed.
if NodeMCU firmware is detected, please do step 4. Otherwise, please do step 5.
if NodeMCU firmware is detected, please do step 4. Otherwise, please do step 5.
4.(NODEMCU FIRMWARE DETECTED) Depending on which firmware is detected, do the following
- Issue the command node.heap(). Do this by typing it in, then clicking send to ESP.
- a response will come with the heap size. The port can now be closed by clicking the ‘close’ button, and the USB cable can be disconnected from the computer.
- Issue the command node.heap(). Do this by typing it in, then clicking send to ESP.
- a response will come with the heap size. The port can now be closed by clicking the ‘close’ button, and the USB cable can be disconnected from the computer.
5.(NODEMCU FIRMWARE NOT DETECTED)Click on the ‘AT v0.20’ tab on the left panel to enter AT commands.
AT command can be issued to the ESP8266 by clicking the ‘AT’ button on the left hand side on the panel. This is just a hello message, and if the ESP8266 is in the correct mode the output should return with an ‘OK’ message. The port can now be closed by clicking the ‘close’ button, and the USB cable can be disconnected from the computer.
AT command can be issued to the ESP8266 by clicking the ‘AT’ button on the left hand side on the panel. This is just a hello message, and if the ESP8266 is in the correct mode the output should return with an ‘OK’ message. The port can now be closed by clicking the ‘close’ button, and the USB cable can be disconnected from the computer.
###Outcomes:You should now be able to
- Install FTDI drivers.
- Achieve communication with ESP8266-01 via a PC.
- Test if the connection of the wiring is done successfully.
ESP8266-012
###Technologies, Tools, and Resources used:
- A Computer.
- Cables.
- A 3.3V capable Serial-USB adapter.
- Micro USB to USB cable.
- ESPlorer IDE.
- ESP8266-012 full evaluation board.
ESP8266-012 Connectivity Guide
Installing drivers for serial to usb adapter
Please refer to the esp8266-01 section for guidance on driver installation.
Please refer to the esp8266-01 section for guidance on driver installation.
Connection wiring between the ESP8266-012 and a serial to USB device
This section shows how to wire up the ESP8266-012 to USB device in order to be able to communicate the ESP8266 device with a terminal.
This section shows how to wire up the ESP8266-012 to USB device in order to be able to communicate the ESP8266 device with a terminal.
- Connect the RxD pin on the ESP8266-12 to the RxD pin on the USB serial device.
- Connect the TxD pin on the ESP8266-12 to the TxD pin on the USB serial device.
- Connect the ground pin on the ESP8266-01 to a ground. This can be done directly by connecting to ground on the usb to serial device, or through a common ground which both connect too.
- Connect the VCC pin on the ESO8266-12 to the VCC on the usb serial device, ensuring that the voltage is 3.3v.
- Ensure the jumper pin between gpio0 and ground is not inserted. This is the two pins just below the ground pin.
Image of a jumper
Refer to the table below for a summary
ESP8266 12 Full Eval. Board | serial-USB | Explanation |
---|---|---|
TxD | TxD | Enable communications to receive and transmit data |
RxD | RxD | Enable communications to receive and transmit data |
GND | GND | Common ground zero voltage reference for all pins |
VCC | VCC 3.3V | Power supply (optional if using batteries) |
Note RxD to RxD and TxD to TxD!! this is due to mislabeling on the evaluation board.
Testing the Connection
Refer to the same section in the esp8266-01 guidance section.
Refer to the same section in the esp8266-01 guidance section.
UART (Universal Asynchronous Transmitter Receiver), this is the most common protocol used for full duplex serial communication. It is a single LSI (large scale integration) chip designed to perform asynchronous communication. This device sends and receives data from one system to another system.
In this tutorial, you will learn the basics of UART communication, and working of the UART.
What is UART?
“UART” stands for Universal Asynchronous receiver-transmitter. It is a peripheral that is present inside a microcontroller. The function of UART is to convert the incoming and outgoing data into the serial binary stream. An 8-bit serial data received from the peripheral device is converted into the parallel form using serial to parallel conversion and parallel data received from the CPU is converted using serial to parallel conversion.
Why UART is used?
Protocols like SPI (serial peripheral interface) and USB (Universal Serial Bus) are used for fast communication. When high-speed data transfer is not required UART is used. It is a cheap communication device with a single transmitter/receiver. It requires a single wire for transmitting the data and another wire for receiving.
UART Interface
It can be interfaced with a PC (personal computer) using a RS232-TTL converter or USB-TTL converter. The common thing between RS232 and UART is they both don’t require a clock to transmit and receive data. They use 1 start, 1 or 2 stop bits and a parity bit for serial data transfer.
Block Diagram
The UART consists of the following core components. They are the transmitter and receiver. The transmitter consists of the Transmit hold register, Transmit shift register, and control logic. Similarly, the receiver consists of a Receive hold register, Receiver shift register, and control logic. In common, both the transmitter and receiver are provided with baud rate generator.
The baud rate generator generates the speed at which the transmitter and receiver have to send/receive the data. The Transmit hold register contains the data byte to be transmitted. The transmit shift register and receiver shift register shift the bits to the left or right until a byte of data is sent/received.
In addition to these, a read or write control logic is provided to tell when to read/write. The baud rate generator generates speeds ranging from 110 bps (bits per second) to 230400. Mostly, microcontrollers come up with baud rate such as 9600, 115200.
How UART works?
To know the working of UART, you need to understand the basic functionality of serial communication. In short, transmitter and receiver use start bit, stop bit and timing parameters to synchronize with each other. The original data is in the parallel form. For example, we have 4-bit data, to convert it into the serial form, we need a parallel to serial converter. Generally, D flip-flops or latches are used to design the converters.
Working of D – Flip-flop
Basic D Flip-Flop
D flip-flop also known as Data flip-flop shifts one bit from the input side to the output side if and only, when the clock changes the transition from high state to low state or low state to a high state. Likewise, if you want to transfer four bits of data you need 4 flip-flops.
Note: Here,
‘D‘ represents input data.
‘CLK‘ indicates clock pulses.
‘Q‘ denotes output data. Now, let’s design a parallel to serial and serial to parallel converter.
Parallel to Serial Conversion
Cascade Connection – Parallel to Serial
Step#1:
Take 4 Flip-flops. The number of flip-flops is equivalent to the number of bits to be transmitted. Similarly, put Multiplexers in front of each flip-flop, but excluding the first one. A multiplexer is placed to combine the data and convert it to serial bits. It has two inputs, one parallel bit data and another from the previous flip-flop.
Step#2:
Now, Load the data at a time in the D flip-flops. It will pull the parallel data and moves the last bit of last flip-flop (four), and then the third bit, second bit and finally the first bit. Now, to reconvert the parallel data into serial form serial to parallel converter is used.
Serial to Parallel Conversion
Cascade Connection – Serial to Parallel Conversion
Step#1:
Take 4 Flip-flops. The number of flip-flops is the same as the number of bits to be transmitted.
Step#2:
Initially, disable the parallel bus. Don’t enable until all bits are loaded. Store the data at the input of the first flip-flop. Now make clock high, this will shift the least significant bit to the input of the second flip-flop and the output of the first one. Similarly, shift all the bits one by one by making the clock pulse high. The converter is in the hold state until all bits are transferred to the output.
Step#3:
Now each flip-flop contains one bit of serial data. Erstwhile all bits are transferred to the flip-flop output, enable the bus. This will make the converter to send all the bits at a time.
Protocol Format
The UART starts the communication with a start bit ‘0’. The start bit initiates the transfer of serial data and stop bit ends the data transaction.
Protocol format
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It is also provided with a parity bit (even or odd). Even parity bit is represented by ‘0’ (even number of 1’s) and the odd parity bit is represented by ‘1’ (odd number of 1’s).
![Serial communication with esp8266wifi Serial communication with esp8266wifi](/uploads/1/2/5/8/125861723/314740861.png)
Transmission
The transmission of data is done using a single transmission line (TxD). Here ‘0’ is considered as space and ‘1’ is known as mark state.
Transmission Frame
The transmitter sends a single bit at a time. After sending one bit, the next bit is sent. In this way, all the data bits are sent to the receiver with a predefined baud rate. There will be a certain delay in transmitting each bit. For example, to send one byte of data at 9600 baud rate, each bit is sent at 108 µsec delay. The data is added with a parity bit. So, 10 bits of data are required to send 7 bits of data.
Note: In transmission, always LSB (Least Significant Bit) is sent first.
Reception
During the reception, RxD line (Receiver) is used for receiving the data.
Example of UART interfacing
This example demonstrates the interfacing of ESP8266 UART with MAX232. But, before I jump into the details of interfacing, let me share the pin details of the Max232 driver.
MAX232 Pinout
MAX232 IC is powered up by 5V supply which includes a capacitive voltage generator to drive 232 level voltages. It comes with dual transmitters also called the driver (TIN, TOUT) and receivers (RIN and ROUT).
Here, I have used ESP8266 (32-bit microcontroller) which has inbuilt UART. The communication can be done with ESP8266 using AT commands via RS232 to TTL level converter (MAX232). The below figure shows the connection of ESP8266 with PC (personal computer).
By requesting valid AT commands through the PC the Wi-Fi chip will respond with an acknowledgment. I don’t want to go in-depth about ESP8266 and it will be explained in the future tutorials.
Here are the steps to implement serial communication with PC.
- Connect Transmitter (TX) of ESP8266 to Receiver (TX) of RS232 to TTL level converter (MAX232) and RX of PC.
- Connect Receiver (RX) of ESP8266 to TX of PC and RX of TTL converter.
ESP8266 Commands
AT command (Sent from PC) | ESP8266 Response (received by PC) |
---|---|
AT<CR><LF> | OK<CR><LF> |
AT+CIPMUX=1 | OK<CR><LF> |
AT+CIPSERVER=1,23<CR><LF> | OK<CR><LF> |
The below screenshot shows the response given by the ESP8266 module.
ESP8266 Commands – Docklight Program
UART vs. USART
Technically, they are not the same. But, the definition is same for both of them. These are microcontroller peripherals that convert parallel data into serial bits and vice versa.
The main difference between UART and USART is, UART supports only asynchronous communication, whereas USART support synchronous as well as asynchronous communication. For easy understanding, here is the comparison between USART and UART.
UART | USART |
---|---|
The Clock is generated internally by the microcontroller. | The sending device will generate the clock. |
The data rate is slow. | The data rate is higher due to external clock. |
Standalone protocol | Supports multiple protocols like LIN, RS-485, IrDA, Smart Card etc. |
The baud rate should be known before transmission. | No need to know the baud rate earlier. |
Suitable for low speed communications | Suitable for high speed communications. |
Reduced energy footprint. | Handles serial communication during high energy consumption |
RS232 and UART
Logic levels represent the operating voltage levels that a device can withstand to operate in a safe zone. Here are the voltage levels for RS232 and TTL.
RS232 Logic:
RS232 Voltage Levels
Logic Level | Voltage Range |
---|---|
Logic High or OFF output | -5V to -15V |
Logic Low or ON output | +5V to +15V |
Logic High or OFF input | -3V to -15V |
Logic Low or ON input | +3V to +15V |
In most cases RS232 levels range from -12V to +12V. For instance, an ASCII value for a character ‘A‘ in RS232 is 65 and 41 in Hexadecimal. So in 8-bit binary format, it is 0100 0001. Here shows the representation of RS232 logic levels for ASCII ‘A‘.
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