Serial protocol design in Raspberry Pi - Step-by-Step Execution

Concept Flow - Serial protocol design

Start Transmission

↓

Send Start Bit

↓

Send Data Bits

↓

Send Parity Bit (optional)

↓

Send Stop Bit(s)

↓

Wait for Acknowledgment

↓

End Transmission

This flow shows how data is sent step-by-step in a serial protocol, starting with a start bit, followed by data bits, optional parity, stop bits, and then waiting for acknowledgment.

Execution Sample

Raspberry Pi

start_bit = 0
 data_bits = [1,0,1,1,0,0,1,0]
 parity_bit = 1
 stop_bit = 1

# Transmit sequence: start_bit + data_bits + parity_bit + stop_bit

This code prepares bits for a serial transmission sequence including start, data, parity, and stop bits.

Execution Table

Step	Action	Bit Sent	Description
1	Send Start Bit	0	Start bit signals beginning of data
2	Send Data Bit 1	1	First data bit sent
3	Send Data Bit 2	0	Second data bit sent
4	Send Data Bit 3	1	Third data bit sent
5	Send Data Bit 4	1	Fourth data bit sent
6	Send Data Bit 5	0	Fifth data bit sent
7	Send Data Bit 6	0	Sixth data bit sent
8	Send Data Bit 7	1	Seventh data bit sent
9	Send Data Bit 8	0	Eighth data bit sent
10	Send Parity Bit	1	Parity bit for error checking
11	Send Stop Bit	1	Stop bit signals end of data
12	Wait for Ack	-	Wait for acknowledgment from receiver
13	End Transmission	-	Transmission complete

💡 Transmission ends after stop bit sent and acknowledgment received

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	After Step 9	After Step 10	After Step 11	Final
bit_index	0	1	2	3	4	5	6	7	8	9	10	11	Transmission Complete
current_bit	-	0	1	0	1	1	0	0	1	0	1	1	-

Key Moments - 3 Insights

Why do we send a start bit before data bits?

The start bit signals the receiver that data is coming, so it knows when to start reading bits. See execution_table row 1.

What is the purpose of the parity bit?

The parity bit helps detect errors in data transmission by making the total number of 1s even or odd. See execution_table row 10.

Why do we wait for an acknowledgment after sending stop bit?

Waiting for acknowledgment ensures the receiver got the data correctly before ending transmission. See execution_table row 12.

Visual Quiz - 3 Questions

Look at the execution_table, what bit is sent at step 5?

A 0

B Start bit

C 1

D Parity bit

💡 Hint

Check execution_table row 5 under 'Bit Sent' column

At which step does the parity bit get sent?

A Step 9

B Step 10

C Step 11

D Step 12

💡 Hint

Look for 'Send Parity Bit' in execution_table under 'Action'

If we remove the stop bit, what happens to the transmission end step?

A Transmission never ends properly

B It happens at step 11 as usual

C It happens earlier at step 10

D Acknowledgment is skipped

💡 Hint

Refer to exit_note and execution_table rows 11-13

Concept Snapshot

Serial protocol sends data bit by bit.
Start bit signals start.
Data bits follow.
Optional parity bit checks errors.
Stop bit signals end.
Receiver sends acknowledgment.

Full Transcript

In serial protocol design, data is sent one bit at a time. The transmission starts with a start bit to tell the receiver data is coming. Then the data bits are sent in order. An optional parity bit can be added to help detect errors. After that, a stop bit signals the end of the data. Finally, the sender waits for an acknowledgment from the receiver to confirm the data was received correctly. This step-by-step process ensures reliable communication between devices like a Raspberry Pi and peripherals.