SPI communication

 

Introduction to Bit Walloping SPI communication via Bit Banging

Communication Interfaces are one of the elements that can be considered when selecting a microcontroller for an undertaking. The designer guarantees that the microcontroller chosen has all the interfaces required to speak with all the other machinery used for the product. The existence of a number of those interfaces like SPI and I2C on microcontrollers continuously will increase the cost of such microcontrollers, and depending on 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 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 data into signals and pulses that govern the nation of an I/O pin of a microcontroller which helps as the Tx pin to send information to the goal tool. To acquire knowledge, the method involves sampling the country of the Rx pin after positive periods that are decided with the aid of the communication baud price. The software units all the parameters needed to acquire this conversation together with synchronization, timing, tiers, etc., which can be customarily determined utilizing dedicated hardware while bit banging isn't used.

When to apply Bit Banging

Bit-Banging is typically utilized when a microcontroller with the specified interface isn't available or switching to a microcontroller with the desired interface is probably too costly. It thus presents a reasonably-priced way of enabling the paired device to talk the usage of several protocols. For example, microcontroller al previously

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 go for specific serial protocols, the method/algorithm for implementing Bit banging is equal throughout all systems.

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

Start

Send jump bit

Wait for the timing to resemble the baud charge of the receiver

Send statistics bit

Wait for a period to correspond with the baud rate of the 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 greater complex. Generally, an interrupt is used to decide while information is available at the receiver pin. This enables making certain the microcontroller doesn't waste too much processing energy. Although specific applications use any of the microcontroller's I/O pins, the probability of noise and mistakes, if no longer probably dealt with, is better. The algorithm to obtain information on the usage of interrupts is defined underneath.

Start

Enable interrupt on Rx pin

When the interrupt is precipitated, achieve the start bit

Wait for timing in keeping with the baud rate

Read the Rx pin

Repeat from four till all facts have been received

Wait for timing according to the baud price

Check for forestall bit

Stop

Bit Banging over SPI

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