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STM32 micros just like any other micro provide hardware for serial communication. As we all know serial communication is a very important tool for debugging, connecting with external hardware like RFID, GPS, GSM modems, etc. and for performing other communication-related tasks. STM32s have several hardware serial (USART) ports. The number of ports available in a STM32 micro is dependent on device family type and the device itself. Typically there are at least 5 serial ports. Apart from the basic serial communication needs, STM32’s USART hardware also have support for LIN, one-wire, smart card protocols, SPI and IrDA. We can even utilize STM32’s DMA controller with USART hardware to achieve high speed automated data communication. Thus these hardware are truly universal synchronous-asynchronous receiver-transmitters.
In any standard serial communication, we need three wires – TX, RX and GND. TX pin is an output pin and transmits data serially to another device’s RX pin. RX pin is an input pin and is responsible for receiving data from another device’s TX pin. https://entrancementrecipe.weebly.com/free-download-daemon-tools-lite-portable.html. The two devices connected in this way must have same ground (GND). There are other pins like CTS and RTS which are used for hardware flow control. Additionally there’s also another pin called CK. It is transmitter’s clock output and used usually in SPI and other modes.
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- Hello, and welcome to this presentation of the STM32 Serial Peripheral Interface or SPI. During protocol-level communication, the DMA can be.
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Depending on package, USART pins are arranged in the following pattern:
BGA100 | LQFP100 | LQFP48 | LQFP64 | Pin Name | USART/UART |
D9 | 67 | 29 | 41 | PA8 | USART1_CK |
C10 | 70 | 32 | 44 | PA11 | USART1_CTS |
B10 | 71 | 33 | 45 | PA12 | USART1_RTS |
C9 | 68 | 30 | 42 | PA9 | USART1_TX |
D10 | 69 | 31 | 43 | PA10 | USART1_RX |
G3 | 29 | 14 | 20 | PA4 | USART2_CK |
G2 | 23 | 10 | 14 | PA0 | USART2_CTS |
H2 | 24 | 11 | 15 | PA1 | USART2_RTS |
J2 | 25 | 12 | 16 | PA2 | USART2_TX |
K2 | 26 | 13 | 17 | PA3 | USART2_RX |
K8 | 51 | 25 | 33 | PB12 | USART3_CK |
J8 | 52 | 26 | 34 | PB13 | USART3_CTS |
H8 | 53 | 27 | 35 | PB14 | USART3_RTS |
J7 | 47 | 21 | 29 | PB10 | USART3_TX |
K7 | 48 | 22 | 30 | PB11 | USART3_RX |
B8 | 79 | – | 52 | PC11 | UART4_RX |
B9 | 78 | – | 51 | PC10 | UART4_TX |
B7 | 83 | 54 | PD2 | UART5_RX | |
C8 | 80 | – | 53 | PC12 | UART5_TX |
Personally I’m interested in LQFP packages, particularly 48 and 64 packages as they are mostly used in the most common STM32 development boards. I suggest locating USART/UART pins before working with them. Typing master full version torrent.
Rs232 Serial Communication Protocol
Things to keep in mind https://entrancementrecipe.weebly.com/virtualfem-30-download-free.html.
- Only USART1 can operate with clocks up to 72 MHz while the rest can operate at 36 MHz maximum. This is because USART1 can get full system clock while the others get half of that.
- USART1 is connected to the high speed APB2 bus while rest are connected to the lower speed APB1 bus. Most communication peripherals are connected with APB1 bus.
- GPIO pins associated with USART hardware must be set as alternate function I/Os and it should be enabled before the hardware modules’ use.
- TX pins should be set as low speed (2 MHz) AFIO push-pull outputs while RX pins should be set as floating inputs. RX pins can also be set as inputs with pull-ups or pull-downs if needed.
- If flow control is not used then the associated flow control pins can be left as GPIO pins. For instance PA8, PA11 and PA12 of USART1 can be used as GPIO pins if flow control is not needed.
- USART/UART pins can be remapped using AFIO_MAPR register. By default, the default pins like PA9 and PA10 for USART1 are used and not remapped elsewhere because this register is by default cleared and hardware remapping is not enabled.
- In exception conditions, APB1RSTR and APB2RSTR registers can be used reset USART/UART hardware.
This is USART register map:
For better view check STM32F10x Reference Manual’s (RM) page 799. These registers are all that are related to USART/UART hardware. Although the registers are 32 bit wide, the upper nibbles are left unused and so they should be written 0s. This is done by hardware too.
For better view check STM32F10x Reference Manual’s (RM) page 799. These registers are all that are related to USART/UART hardware. Although the registers are 32 bit wide, the upper nibbles are left unused and so they should be written 0s. This is done by hardware too.
Serial Communication Program
It should also be noted that STM32s operate at 3.3V and so avoid using 5V devices directly. Although some STM32 pins are 5V tolerant I would suggest avoiding 5V device interfacing. I will recommend using popular MAX232-based circuit for interfacing with RS232-level ports or USB-TTL converters like FT232, CP2102, PL2303, etc. https://entrancementrecipe.weebly.com/download-jre160-31.html. for connecting with PCs and laptops. I’m using a FT232R breakout board here.
Serial Communication
If needed a logic level converter may also be used.