It is used for the Serial interface. Other devices can be controlled through the terminal for text interface through RS 232.
It was introduced in 1960 and since its introduction, it was known as 𝐑𝐒-𝟐𝟑𝟐 but it is now officially called 𝐓𝐈𝐀-𝟐𝟑𝟐.
The TIA-232 describes mostly the 𝟐𝟓-𝐩𝐢𝐧 connector, the 𝟗-𝐩𝐢𝐧 connector description is also available. The 25-pin connector was not of much use, so the manufacturers started to use the 9-pin connection.
The original standard i.e the 25 pin connection has a secondary tx/rx. It’s 2 interfaces in 1.
Although the RS232 𝐝𝐨𝐞𝐬 𝐧𝐨𝐭 𝐮𝐬𝐞 𝐭𝐡𝐞 𝐜𝐥𝐨𝐜𝐤 𝐬𝐢𝐠𝐧𝐚𝐥, the original 25 pin interface uses some clock signals such as
– Transmit clock from DCE
– Receive clock
– Transmit clock from DTE
𝐓𝐡𝐞 𝟗-𝐩𝐢𝐧 𝐜𝐨𝐧𝐧𝐞𝐜𝐭𝐨𝐫 𝐰𝐚𝐬 𝐬𝐭𝐚𝐧𝐝𝐚𝐫𝐝𝐢𝐳𝐞𝐝 𝐚𝐬 𝐄𝐈𝐀/𝐓𝐈𝐀-𝟓𝟕𝟒
“RS-232 is an interface between Data Terminal Equipment and Data Circuit Terminating Equipment Employing Serial Binary Data interchange.”
The RS 232 uses 2 conditions, the 𝐒𝐩𝐚𝐜𝐢𝐧𝐠 𝐂𝐨𝐧𝐝𝐢𝐭𝐢𝐨𝐧 and the 𝐌𝐚𝐫𝐤𝐢𝐧𝐠 𝐂𝐨𝐧𝐝𝐢𝐭𝐢𝐨𝐧.
This terminology comes from the era of telegraphs/paper tapes where the marking condition means the mark/hole on the paper and the spacing condition means an empty region on the paper.
A simple working example would be:
When a key is pressed and if you capture a single shot signal on the oscilloscope, a signal will be generated spanning from -𝟔𝐕 𝐭𝐨 >+𝟑𝐕.
For the interchange of signals, it is said to be in marking condition when the signal is greater than -3 Volts w.r.t to Signal common and the Signal is in spacing condition when the signal is more than +3 Volts w.r.t to the circuit. The region between +- 3 Volts is said to be the 𝐭𝐫𝐚𝐧𝐬𝐢𝐭𝐢𝐨𝐧 𝐫𝐞𝐠𝐢𝐨𝐧. The signal state is undefined when the signal is in the transition state.
The RS 232 does not use a clock signal. So when do the devices know which bit is being delivered when or w𝐰𝐡𝐢𝐜𝐡 𝐛𝐢𝐭 𝐭𝐨 𝐫𝐞𝐚𝐝 𝐰𝐡𝐞𝐧?
The devices should agree on the data rate or popularly known as 𝐁𝐚𝐮𝐝 𝐑𝐚𝐭𝐞.
Commonly used Baud rates are 4800,9600,38400,57600,115200…
If we select 9600 as the baud rate, then we get 1/9600 i.e ~0.000104167 i.e 1 bit every 4 microseconds
The first bit is the start bit i.e 1. The next 8 bits are data bits.
The least significant bit is the first.
After transitions of the last bit, the signal stays low until the next bit press. It does so as it requires a minimum amount of ideal time for transmission between 2 characters.
Although there are many new protocols, RS-232 is still widely used in many industries.
How was your experience with RS-232? Did you use it?
#embedded #embeddedsystems #cprogramming #protocols #rs232 #learning #reach #Tia232 #embeddedprotocols
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