Interfacing with the ElecronicsV2 Development Board
In previous blog we covered a brief overview of how the OLED display works in microscopic level and also understood various types of OLED displays available in the market . In this blog we’ll be discussing how to configure the SSD1306 display with the microcontroller and we’ll be making the embedded driver as well.128×64 display is a dot matrix display , hence 128×64 =8192 total pixels . It is by turning on/off these pixels we display graphical image of any shape . It is the current provided to each pixel that varies the brightness. HARDWARE DESCRIPTION OLED Display chosen is driven by SSD1306 Driver IC although they are other ICs such as SSD1331 which can be used to drive the display . These ICs are CMOS OLED Driver controller for dot-matrix system . OLED has 256 brightness steps .Besides 128×64 , 128×32 display resolution is also available. Specification of ssd1306 128×64 OLED Display Type: OLED (Organic Light Emitting Diode) Display Size: 128×64 pixels Display Driver: ssd1306 Display Colors: Monochrome (White), Yellow, and Blue Operating Voltage: 3.3V to 5V Interface: I2C Operating Current: ~20mA Display Structure OLED DISPLAY is mapped using GDDRAM page structure OF SSD1306 GDDRAM or graphic display ram is a bit mapped static RAM . It holds the bit pattern to be displayed. The GDDRAM having size 128×64 is divided into 8 pages from PAGE 0 TO PAGE 7 which is used for monochrome matrix display . When data bit D0 – D7 is sent the row0 gets filled with D0 and D7 is written into the bottom row. Display has 64 rows , 128 columns divided into 8 pages . Each page has 128 columns and 8 rows. Display 128 columns known as segments For displaying the graphical data in the first location , page address and column address both are set to 0 with the end address of page and column also being selected End of column and End of the page is 7FH and 07H respectively SSD1306 BLOCK DIAGRAM PIN ARANGEMENT SSD1306 FUNCTIONAL BLOCK DIAGRAM SSD1306 BLOCK DIAGRAM PIN ARANGEMENT SSD1306 FUNCTIONAL BLOCK DIAGRAM ADDRESSING MODE 1. PAGE ADDRESSING MODE 2.Horizontal Addressing Mode 3.Vertical Addressing Mode 1. PAGE ADDRESSING MODE In page addressing mode, after the display RAM is read/written, the column address pointer is increased automatically by 1. If the column address pointer reaches column end address, the column address pointer is reset to column start address but page address pointer not points to next page. Hence, we need to set the new page and column addresses in order to access the next page RAM content. We need to set lower two bits to ‘1’ and ‘0’ for Page Addressing Mode. In page addressing mode, the following steps are required to define the starting RAM access pointer location: Set the page start address of the target display location by command B0h to B7h. Set the lower start column address of pointer by command 00h~0Fh. Set the upper start column address of pointer by command 10h~1Fh 2.Horizontal Addressing Mode In horizontal addressing mode, after the display RAM is read/written, the column address pointer is increased automatically by 1. If the column address pointer reaches column end address, the column address pointer is reset to column start address and page address pointer is increased by 1. When both column and page address pointers reach the end address, the pointers are reset to column start address and page start address We need to set last two digits to ‘0’ and ’0’ for horizontal addressing mode. 3.Vertical Addressing Mode In vertical addressing mode, after the display RAM is read/written, the page address pointer is increased automatically by 1. If the page address pointer reaches the page end address, the page address pointer is reset to page start address and column address pointer is increased by 1. When both column and page address pointers reach the end address, the pointers are reset to column start address and page start address. We need to set last two digits to ‘0’ and ’1’ for vertical addressing mode. In normal display data RAM read or write and horizontal/vertical addressing mode, the following steps are required to define the RAM access pointer location: Set the column start and end address of the target display location by command 21h. Set the page start and end address of the target display location by command 22h. Hardware Pinout SDAThis pin is used to send data between master and slave with the acknowledgement of the master SCLThis is a clock signal that helps keeps the process in synchronization VCCA power supply of 3.3 V is required . More than 3.3V may damage the module GNDThis ground pin is connected to the ground supply ALGORITHM Select the I2C slave address and specify the operation that will be performed i.e Read 0x79 or Write 0x78. #define SSD1306_I2C_ADDR 0x78 Set the clock divide ratio and oscillator frequency . Bit 3-0 sets the clock divide ratio , Bit 7-4 sets the oscillator frequency SSD1306_WRITECOMMAND(0xD5); //–set display clock divide ratio/oscillator frequency SSD1306_WRITECOMMAND(0xF0); //–set divide ratio Set the multiplex ratio switching to any value ranging from 16-63 SSD1306_WRITECOMMAND(0xA8); //–set multiplex ratio(1 to 64) Display start line addressing in which the starting address of the display ram is determined . In our case this is set to zero and RAM row 0 is mapped to col 0 SSD1306_WRITECOMMAND(0x40); //–set start line address Set memory addressing mode using page addressing mode, horizontal addressing mode, vertical addressing mode. SSD1306_WRITECOMMAND(0x10); //00,Horizontal Addressing Mode;01,Vertical Addressing Mode;10,Page Addressing Mode (RESET);11,Invalid SSD1306_WRITECOMMAND(0xB0); //Set Page Start Address for Page Addressing Mode,0-7 Set column address using a triple byte first specifies the column setting , second column start and third column end . Do the same for the page SSD1306_WRITECOMMAND(0x00); //—set low column address SSD1306_WRITECOMMAND(0x10); //—set high column address Set pre-charge period and VCOMH deselect level SSD1306_WRITECOMMAND(0xDB); //–set vcomh Entire display is on using A4H and A5H command SSD1306_WRITECOMMAND(0xA4); //0xa4,Output follows RAM content;0xa5,Output ignores RAM content The normal functionality of the
In the last blog we discussed what a keypad module is . In this blog we will be discussing how to interface a 4×4 membrane type keypad module with stm32 microcontroller. Although the keypad module can be configured using both polling and interrupt methods , in this blog we will be discussing the interrupt method as it takes less CPU cycles , also since interrupt doesn’t require constant CPU attention. Keypad module along with stm32 microcontroller finds applications in industrial machines as well various projects such as bluetooth door lock , scientific calculator etc. Hardware description The keypad module consists of 3 layers:- The top layer is made of polymer which usually is the printed graphic overlay . It defines the function of each button in the keypad module . It is heat and water resistant and also prevents from electric discharge. The middle layer that usually consists of dome shaped stainless buttons which upon touch makes contact with the bottom layer completing the circuitry. The bottom layer consists of printed circuitry made of conductive material such as silver or copper oxide. When a key is pressed the dome shaped buttons make contact which completes the circuit and this information is conveyed to microcontroller in the form of signal by the external ribbon. The 4×4 keypad module chosen by us consists of numbers from 0 to 9 along with 2 characters ‘*’ and ‘#’ in the first 3 columns while the last column consists of alphabets A, B ,C , D. The internal circuit diagram of the keypad module Internal Circuit Working Circuit Diagram As can be seen one end of each button is connected to a wire that is then connected to the connector pin as row and other end is connected to another wire which is the column wire. Both the row and column wires helps us pinpoint the button that is pressed. The connection are then made to the MCU in which the row part is configured as GPIO output and written high in our case this will be PA15, PB3, PB4 , PB5 pins the column part is then written as GPIO EXTI interrupt which will get triggered in case of a button push , this will be PB6,PB7,PB8,PB9 in our case . As can be seen in the figure since each row from one side is already HIGH once the connection is made by pressing the button this is read by the MCU pins PB6,PB7,PB8,PB9 and the interrupt is raised which is detected in the rising edge. Besides the keypad module connection UART1 is also enable as PA9 as TX and PA10 as RX This will be used to display the button pressed when the interrupt is fired using teraterm or similar software. ALGORITHM Configure pins PA15,PB3,PB4,PB5 as output pins with no pull up and low frequency Configure pins PB6, PB7,PB8, PB9 as interrupt pins with no pull up and interrupt detection on the rising edge Set the NVIC priority as 0 and enable IRQ Incoming interrupts are handled using EXTI callback function Initialize the UART1 function , configure the parameters and select PA9 as tx and PA10 as RX Hal tick function is called to use key debouncing and prevent unwanted input noise from the buttons 2 variables currentMillis and previousMillis are declared which prevents extra activations or slow functions from triggering the interrupts this is done by subtracting the former from latter and the difference should be greater than 10 Each row is written GPIO 1 and checked if the corresponding column is gpio 1 as well. in case both the conditions are satisfied the interrupt is raised and a keypress is detected The keypressed is displayed on Teraterm or similar software using UART1 SOFTWARE CONFIGURATION Open the stm32cube ide and configure the sys mode, select the debug as serial wire and time base source as systick . In the GPIO section select the pins PA15, PB3,PB4, PB5 as output pins set parameters to default which is GPIO pins to no pull and operations at low frequency . Next select the pins PB6,PB7,PB8,PB9 as EXTI interrupt pins also in the NVIC section enable the line EXTI line [9:5] interrupts .Also configure the GPIO EXTI as interrupt rising which would read the occurrence of the interrupt on the rising edge of the wave and operation as low frequency . The NVIC priority is set to 0 (the highest) and the IRQ is enabled. All the button or key presses are handled by HAL_GPIO_EXTI_Callback function in which the keydebouncing is applied and each row is written GPIO HIGH incase a button press the respective column goes high as well raising the interrupt and the corresponding key is displayed using UART .for eg-The button press such as key 9 is detected when both PB3 and PB7 is HIGH as due to the press a connection is made and an interrupt is raised. Also in the connectivity section select the UART1 set the parameters such as mode to asynchronous , baud rate 115200, Word-length as 8 bits , Stop bits as 1 , mode as TX and RX , hardware flow control as none and oversampling rate as 16 . The UART1 has pin PA9 as TX and PA10 as RX . The uart is used to display the key that is pressed on a teraterm or similar software with baud rate set to 115200 SOFTWARE CONFIGURATION CODE #include “main.h” #include #include /* Private includes ———————————————————-*/ char buffer[32]={0}; /* USER CODE BEGIN Includes */ /* USER CODE END Includes */ /* Private typedef ———————————————————–*/ /* USER CODE BEGIN PTD */ /* USER CODE END PTD */ /* Private define ————————————————————*/ /* USER CODE BEGIN PD */ /* USER CODE END PD */ /* Private macro ————————————————————-*/ /* USER CODE BEGIN PM */ /* USER CODE END PM */ /* Private variables ———————————————————*/ UART_HandleTypeDef huart1; /* USER CODE BEGIN PV */ GPIO_InitTypeDef GPIO_InitStructPrivate = {0}; uint32_t previousMillis = 0; uint32_t currentMillis = 0; uint8_t keyPressed = 0;
Table of Contents Many of you may be familiar with the RFID module MFRC522, but I’m willing to bet that most of you have only interfaced this module with an Arduino and the Arduino IDE environment. However, if you need to use the RFID module with other MCUs, you may find yourself at a loss for how to proceed. If this is the case, you’ve come to the right place. In this blog, I will show you how to create a device driver for the RFID Module MFRC522, allowing you to interface it with any Host MCU. If you’re not sure what we mean by interfacing with a Host MCU or why it’s necessary, be sure to check out our blog for more information. Continuing with the MFRC522 RFID reader interfacing to host MCU, Objective would be to interface this module with Host MCU’s like of NXP Semiconductors, STMicroelectronics or other vendors MCU’s. Will make the driver to interface the RFID Reader with any MCU, not unlike just with Arduino and Arduino IDE environment. You just need to change 2-3 low level API’s for running it on different MCU’s, would be telling about it in below sections. In this blog we are going to write the driver in c++ language. Before proceeding further would recommend viewers go through, the following set of blogs and videos to have a better understanding. Prerequite, better to have: Viewers can refer to this blog to know about RFID technology in detail. or can watch this video which is in animated format to know about RFID technology. RFID Reader MFRC522: Overview and Datasheet Explanation( Highly recommended to go through at first) MIFRAME RFID Tags: Overview and Datasheet Explanation About Serial Communication Protocols To know about What are Microcontrollers and introduction on them Hardware Connection of MFRC522 Reader module MFRC522 Module has 8 pins exposed out, which can be categorised into 3 parts: Communication pins, Power Supply Pins and Additional Pins. As explained below Communication Pins Power Supply Pins Additional Pins Logic Analyzer Communication Pins 4 pins are communication pins, that would be connected to Host MCU either using SPI, I2C, or UART. MFRC522 Communication Pins We would be making the connection using the SPI peripheral. Here I am referencing out hardware connection with 2 microcontrollers: NXP Semiconductors S32K144 MCU and STMicroelectronics STM32F103 MCU. STMicroelectronics STM32F103 would be using SPI-1 Instance and S32K144 would be using LPSPI-0 Instance.  Power Supply Pins 2 pins are for Power Supply Connection, which would be used for powering the RFID reader. One can power the MFRC522 Reader via Host MCU. Connect the VCC and GND pins with the Host MCU Power pins. Make sure, you supply MFRC522 with 3.3 V, don’t power it with 5V. MFRC522 Power supply connections Additional Pins There are 2 additional pins on MFRC522: IRQ and RST pins. IRQ pin is an interrupt pin, that is used for alerting the HOST MCU when an RFID tag is in the vicinity. Read about the IRQ pin and interrupts in MFRC522 from here. RST pin would be not used for this project. Logic Analyzer These connections are for debugging and understanding purposes. By connecting the logic analyzers, we would be able to see how literally SPI communication and what commands we are sending, and what responses we are getting in bit and byte levels. Would recommend doing this step, as it makes the understanding clear at the root level. It would hardly take a couple of minutes to setup this. For connecting the logic analyzer, connect the Channel1,3,5,7 of the logic analyzer with communication pins. I am using the Salae logic analyzer, which is readily available. viewers can refer to this video on Gettobyte Youtube channel on how to set up logic analyzer connections, hardware, and software. Logic Analyzer MFRC522 Functional Description API’s MFRC522 has a set of functional descriptions, on which the whole of the working of MFRC522 depends. To write the driver of MFRC522, it’s important to have an understanding of those functional blocks. Reading from the datasheet could be tiering, hence viewers can read and understand from here. MFRC522 Host Interfaces MFRC522 FIFO MFRC522 CRC MFRC522 Interrupts MFRC522 Time Unit MFRC522 Command Set MFRC522 Host Interfaces MFRC522 Host Interface API’s We are going to connect MFRC522 via the SPI interface to the host MCU. SPI configurations: MSB is sent first 8 Bits per transfer The clock is Low when inactive(CPOL=0) Data is valid on Clock Leading Edge(CPHA=0) Enable line is Active LOW SPI Address Byte These address bytes are of 6 bits. When sending the address byte, MSB should tell whether we have to perform a read/write operation on that address. LSB is always set to logic 0 when sending the address byte. Thus you would find in the below driver that MFRC522 registers which are defined in GB_MFRC522.h have been left shifted 1 bit so that the MSB bit can be configured whether to perform a Read or write operation on that register address. SPI Read Data To read the data, Host MCU will send the register address at the MOSI line with LSB as 1 and then in MISO, it would get the data. This would be performed via a low-level function, that is reading one single byte from the address GB_reg which is sent in its argument. uint8_t GB_MFRC522_ReadRegister(PCD_Register GB_reg); For e,g we have to read the version of the MFRC522, which can be done via VersionReg(ox37): uint8_t v = GB_MFRC522_ReadRegister(VersionReg); So it would be left shifted first: 0x37<<1 = 0x6E(So that can configure MSB for read and Write operation). And then as we want to perform a read operation at this register, so need to write MSB with 1. We will Or above value with 0x80( See definition of uint8_t GB_MFRC522_ReadRegister(PCD_Register GB_reg): 0x6E | 0x80 = 0xEE. As per the datasheet, reading this register would give either 0x92 or 0x91.(Refer the datasheet for in-depth-description of this register). In logic analyzer reading from the MFRC522 would look like this: MFRC522 version
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