Introduction to Bit Walloping SPI communication via Bit Banging

 

Introduction to Bit Walloping SPI communication via Bit Banging

Communication Interfaces are one of the elements which can be considered while selecting a microcontroller to be used for a undertaking. The designer guarantees that the microcontroller being selected has all of the interfaces required to speak with all the other components to be used for the product. The existence of a number of those interfaces like SPI and I2C on microcontroller continuously will increase the cost of such microcontrollers, and depending at the BOM budget it may make a favored microcontroller now not less expensive. In situations like those the strategies like Bit Banging are available in to play.

What is Bit Banging?

Bit banging is a method for serial conversation in which the entire communication procedure is treated via software in preference to committed hardware. To transmit information, the method includes the use of software to encode the information into signals and pulses that are used to govern the nation of an I/O pin of a microcontroller which serves as the Tx pin to send information to the goal tool. To acquire information, the method involves sampling the country of the Rx pin after positive periods that is decided with the aid of the communication baud price. The software units all the parameter needed to acquire this conversation together with synchronization, timing, tiers and so on., which can be normally determined by means of dedicated hardware while bit banging isn't used.

When to apply Bit Banging

Bit-Banging is typically utilized in situations in which a microcontroller with the specified interface isn't available or whilst switching to a microcontroller with the desired interface is probably too costly. It thus presents a reasonably-priced way of enabling the identical device to talk the usage of several protocols. A microcontroller that is previously enabled for UART verbal exchange best, may be equipped to speak the usage of SPI and 12C thru bit banging.

Algorithm for Serial Communication thru Bit Banging

While the code to put in force bit banging might also vary throughout numerous microcontrollers and may additionally vary for distinctive serial protocols, but the method/algorithm for implementing bit banging is the equal throughout all systems.

To ship statistics for example the pseudo-code underneath is rummage-sale;

Start

Send jump bit

Wait for timing to resemble with the baud charge of receiver

Send statistics bit

Wait for period to correspond with the baud rate of receiver once more

Check if all records bits were despatched. If no, go to 4. If sure, goto 7

Send stop bit

Stop

Receiving data tends to be a bit bit greater complex, generally an interrupt is used to decide whilst information is available at the receiver pin. This enables make certain the microcontroller doesn’t waste too much processing energy. Although certain applications use any of the microcontrollers I/O pins but the probabilities of noise and mistakes, if no longer probably dealt with, is better. The algorithm to obtain information the usage of interrupts is defined underneath.

Start

Enable interrupt on Rx pin

When interrupt is precipitated, achieve start bit

Wait for timing in keeping with the baud rate

Read the Rx pin

Repeat from four till all facts has been received

Wait for timing according to the baud price

Check for forestall bit

Stop

Bit Banging over SPI

As mentioned above, bit thumping for different protocols paintings otherwise and it’s accordingly crucial to read approximately each protocol, to understand facts framing and clocking earlier than trying to implement. Taking the SPI mode 1 for example, the bottom fee of the clock is usually zero and information is usually despatched or received at the rising fringe of the clock. The judgement drawing for the SPI Mode 1 conversation protocol is shown below.

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