Electronics > Beginners
RS232 Testing
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Spark-Doctor:
Hi All
I am trying to get to grips with RS232 communications. Could anyone tell me the easiest way to set up a test with a Rigol DS1054Z so i can see the signals.
many thanks
Ian
ebclr:
Set voltage to 2V / Div and use a probe on X10 mode ( RS232 can go +12 -12 in the worst cade scenario ) Just connect one probe on RX and GND, another probe on TX and GND, adjust the time base according to the baud rate , supposing some communication is happening between your devices, you will see one signal for tx and another for RX. If you have the decoder option enabled, you can even see in data format
SL4P:
There’s not much to ‘see’ other than an idle signal with bursts of ‘data.’ shaking the lines as they are transmitted.
Keep in mind that across each ‘byte’ transferred, you’ll see a start bit, followed by the data bits, an finally the optional parity and stop bits.
If the data is ‘slow’ enough, you can count off the bits, and decode the byte value in your head ... that gets boring very quickly- or use a protocol decoder to make it easier.
Electro Fan:
Connect a probe as ebclr described to the TX and GND pins on a RS232 port on a PC. Set the controls as per page 7-7 in the Rigol 1054 manual to decode the data. Try using both ASCII and binary settings. On ASCII you will see the Byte characters - try adjusting the time base to get the characters to fit neatly in the green decoder boxes. On binary you will effectively see 1s and 0s*; look for an ASCII table on the Internet and you will get a sense of how the bit (binary digit) patterns represent the Byte characters. The ASCII encoding plus the asynchronous timing (start and stop) bits, plus the parity bit all turned “on and off” (high and low) as reflected by the amplitude (~ +/- 12 Volts) in a serial stream at the specified baud/bit rate will help you visualize RS-232 in operation.
*Toggle the 1s and 0s, effectively the on and off or in this case the high and low states by using the control for the negative logic (the convention) for RS-232 using 0 as high and 1 as low to see the impact on the decodes; likewise try toggling the between the Least Significant Bit and the Most Significant Bit to see the impact on the decodes. Keeping a copy of the ASCII table will help (but technically the RS-232 spec is an electrical (and mechanical) spec that focuses on signaling and timing - which is separate from the ASCII standard.)
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