standard for serial communication
Factsheet
EIA-232 Standard Interconnection of Data Terminal Equipment with a Communications Channel
Status Active
Year started 1960 (66 years ago) (1960)
EIA-232 Standard Interconnection of Data Terminal Equipment with a Communications Channel
Status Active
Year started 1960 (66 years ago) (1960)
Wikipedia
en.wikipedia.org › wiki › RS-232
RS-232 - Wikipedia
2 weeks ago - In August of 1969, the EIA published EIA RS-232-C: Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange. This revision dropped the voltage down to 12 Vpp and introduced the use of Data Communication Equipment (DCE) modems with the ...
Texas Instruments
ti.com › lit › pdf › slla544 pdf
Application Report RS-232 Frequently Asked Questions ABSTRACT
common ground (Figure 1-1). To be more specific, the driver output is Logic 0 when the voltage is between +5 V
Videos
Biamp
support.biamp.com › biamp control › biamp control technologies
RS-232 Everything you need to know - Biamp Cornerstone
April 13, 2022 - According to the standard, the high level can range between -15 and -3 V and the low level can range between 3 and 15 V. The voltage level of the RS-232 transmitter significantly impacts the total transmission length of the line, so the closer ...
Top answer 1 of 2
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From the parts (complementary BJT transistors and discretes near the connector) I think it's a non-standard RS-232 port that idles at 0V rather than -9 or whatever.
That will work with most RS-232 receivers- they typically have a threshold of + 2-3V.
The measurement of 0V idle would tend to confirm that.
That said, it's hard to be 100% sure, so there is some risk.
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The idle level of asynchronous serial communication is logical "1". Unless the device is constantly sending a lot of "0" bits, you can use this fact.
If the wires transport so-called TTL levels, the idle level will be a positive voltage near the digital supply voltage. Commonly this is 5 V or 3.3V.
If the wires transport RS232 levels, the idle level will be a negative voltage, commonly between -3 V and -15 V. Many interfaces only provide about -5 V, so be prepared.
So measure the TX output in reference to Ground, you can use a simple multimeter. If it is some positive voltage between 2 and 5 V, most probably it is "TTL" level. If it is some negative voltage between -2 and -15 V, most probably it is RS232 level.
If you happen to have an oscilloscope, even better. Measure the TX output and look at the levels: TTL levels "swing" between near-positive-digital-supply and near-ground; RS232 levels "swing" between positive and negative voltages of similar magnitude.
DigiKey
digikey.com › en › maker › blogs › 2023 › understanding-the-rs-232-standard
Understanding the RS-232 Standard
October 25, 2023 - In contrast, RS-232 represents a logic 1 using a negative voltage between -15V and -3V. Conversely, the protocol encodes zeros using a positive voltage between +3V and +15V. Therefore, RS-232 traditionally employs negative voltages and uses ...
Analog
analog.com › home › resource library › technical articles › fundamentals of rs-232 serial communications
Fundamentals of RS-232 Serial Communications | Analog Devices
November 4, 2025 - The "basic nine" signals used in ... is described below. Note that for the following signal descriptions, ON refers to a high RS-232 voltage level (+5V to +15V), and OFF refers to a low RS-232 voltage level (-5V to -15V)....
Fly-Wing
flywing-tech.com › home › tutorials › rs232 serial communication protocol:basics, working, and comparison
RS232 Serial Communication Protocol:Basics, working, and comparison - Fly-Wing
November 20, 2025 - Another works as a voltage inverter, generating –10V. The remaining three capacitors act as bypass capacitors for the Vcc, V+, and V– pins. RS232 is a dependable and commonly used serial communication protocol in the electronics industry.
Reddit
reddit.com › r/ece › voltage levels for rs232
r/ECE on Reddit: Voltage Levels for RS232
May 10, 2022 -
I am reading a lot of different information on the internet. Some say that RS232 operates between -12 and +12, others say -15 to +15 and -25 to +25. Is there a set value for the voltages or can it vary with use.
Top answer 1 of 3
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RS-232-C (which is most commonly used) is designed for +/- 15V operation, though it's likely that +/- 12V will work fine too due to tolerance. RS-232-D allows for +/- 25V, though I have not seen this in common use.
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There is a standard for RS-232. It explains voltage levels, among other things. Google it. There is a lot of leeway. I think +5 V and - 5 V levels are legal, up to maybe +25 V and -25 V. But don't quote me on that. Also, I think the load impedance might be in the 3K or 5K ohm range.
Texas Instruments
ti.com › lit › SLLA607 pdf
Application Note RS-232 Glossary and Selection Guide Parker Dodson
must recognize a voltage from –3 V to –15 V as logic 1 and voltages between 3 V and 15 V to be a logic 0
Codrey Electronics
codrey.com › home › embedded systems › what is rs232 protocol and how it works?
What is RS232 Protocol and How it Works? - Codrey Electronics
November 11, 2020 - The line voltages of RS232 range from -25V to +25V.
Advantech
advantech.com › home › support › resources › what is rs-232? fundamentals of the protocol
What is RS-232? Fundamentals of the Protocol - Advantech
October 22, 2018 - Voltage levels are defined as a range from -12 to +12 Volts. RS-232 is also single-ended. This means that a single electrical signal is compared to a common signal (Ground) to determine binary logic states.
Anderson Corporation
andcorp.com.au › fibre talk › rs232 | breaking down crucial information for you!
RS232
February 11, 2025 - RS-232 serial communication uses the Universal Asynchronous Data Receiver and Transmitter (UART) to transmit data between a computer and peripheral devices like printers. Since microcontrollers cannot efficiently handle these voltage levels, connectors are used between RS-232 signals.
Cable Matters
cablematters.com › cable matters › blog › computer accessories › what is rs232? understanding the classic serial communication standard
What is RS232? Understanding the Classic Serial Communication Standard | Cable Matters Blog
February 14, 2025 - In RS232 communication, positive voltage, typically between +3 to +25 volts, is used to represent a binary '0', while negative voltage, ranging from -3 to -25 volts, denotes a binary '1'. This signal voltage polarity, or the direction of the ...
Test & Measurement Tips
testandmeasurementtips.com › home › testing and measurements with rs-232
Testing and measurements with RS-232
December 8, 2017 - The original RS-232 was less ambitious than more recent electronic bus protocols. One problem with the earlier design was that use of large voltage swings and the need for both positive and negative supplies resulted in excessive power consumption. Because of the voltage swing, maximum speed was limited.
Weschler Instruments
weschler.com › blog › introduction to rs-232 devices
RS-232 Devices - Everything You Need to Know
February 22, 2023 - Overview RS-232 devices use single-ended signaling. Data is sent as a 0 or 1 voltage level, referenced to signal ground. This requires fewer wires to transmit information than the differential signaling used in most serial communication standards.
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TALtech
taltech.com › support › serial_intro
RS232 and Serial Communications – TAL Technologies
Any electrical noise affects all lines in the optically isolated cable equally – including the signal ground line. This causes the voltages on the signal lines relative to the signal ground line to reflect the true voltage of the signal and thus canceling out the effect of any noise signals.
Eaton
tripplite.eaton.com › products › rs-232-serial-to-usb-adapters
RS232 Cable and Connectors Explained | Eaton
The RS232 standard defines voltage levels for logical 1 and logical 0. Valid signals are in the range of +3V to +15V (logical zero) or −3V to −15V (logical one) as compared to the 0V ground (GND) pin.
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ELECTRICAL TECHNOLOGY
electricaltechnology.org › home › communication › what is rs232 serial communication protocol and how it works?
What is RS232 Serial Communication Protocol and How it Works?
May 6, 2020 - RS232 Serial Communication Protocol - Working, Specifications & Applications. Characteristics of Serial Communication. How RS232 Works? DB9 Male & Female Connector & Pinout
Vaia
vaia.com › voltage levels
Voltage Levels: RS232, RS422, TTL | Vaia
November 6, 2023 - Yet, it's conventional to find voltages representing logic 1 as -3V to -25V, and logic 0 as +3V to +25V. It's important to note that RS232 doesn't define specific voltage levels. Rather, it merely requires that the driver output should have a differential voltage that exceeds +/- 3V under specific ...