Communicating with Multiple Electronic Test Instruments using RS232
Genetix
Posts: 1,742
I would like to use the Propeller to automate a test procedure where we currently write down the data values from each piece of electronic test equipment.
There are 3 devices that are used one at a time and each has an RS232 port as well as commands for changing the operating modes and outputting the current measurement value.
I know for a fact that 2 of the devices use RS232 converter chips and my guess is that the 3rd does also.
I would like play it safe and use a 3.3 Volt version of the ADM1181A if one exists; This was the chip that Parallax used on the RS232 AppMod.
Do I need to have 3 sets of Serial to the Propeller with RS232 converters or each or is there a way to Multiplex them into 1 serial connection to the Propeller?
2 of the devices use handshaking and the 3rd just has Rx and Tx.
Comments
Unless you're pressed for cogs in your program, the easiest route is definitely to use separate ports with Parallax Serial Terminal. You may have to modify it a bit to accommodate handshaking. (You didn't specify whether it was hardware of xon/xoff.)
-Phil
Hardware handshaking can usually be ignored/tied as long as the byte rate is kept slow enough to not trigger needing it. The exception is when in half-duplex wiring like RS485. Then the data direction has to be controlled.
Sure, that's a common demand, so many are out there, like ADM3232E ADM3202 etc
Usually, no one bothers to multiplex on the RS232 side, but it certainly is possible.
That side has the ESD ratings and is +/- 5V so any switch has to match.
The RS232 drivers are cheap enough, and you can hop a UART onto any number of prop pins, if you are using one at a time.
What baud rates do you need, and what do the handshake lines do ?
One of the devices is a pressure meter and it only uses Rx and Tx at 115200 8N1.
In QuickSend mode it sends data every 1/2 second.
Another is a power meter that uses Rx, Tx, DTR, and DSR at 9600 8N2.
The last is a scale of which we have several different models.
One uses Tx, Rx, CTS, and DTR at 1200 7O1.
Another uses Tx, Rx, DSR, RTS, and CTS at 2400 7E1, but I have a note that DSR is connected to Ground and that RTS and CTS are connected together.
I see there is an ADM3101E that has 1 Tx and 1 Rx, and there is the ADM3202 that has 2 Tx and 2 Rx but also comes in a DIP.
Both are 3.3V with 15kV protection.
Devices like that can often be used as "simplex" connections. Where just the single data out pin, labelled rx, from the device is connected because the default is regular data reporting with no config needed. Or the config is done with the menus of the built-in control panel.
Hmm, seems ideally you need a bit more than 1+1 handshake line, but if you want DIP and 3.3V, that's looking a challenge.
Most 5V parts have TTL logic in, so you just need to use a series R, or a level shifter on the output pins to the Prop.
jmg,
Both of those chips will take a 3.3V Vcc so I thought that means they will work with the Propeller.
evanh,
I believe the instruments need to be commanded to output data; I know for a fact that the pressure meter does.
I imagined that the Propeller would do most of the work, freeing the tester to do the things that are best done by humans.
In the future I could use the Propeller to either perform the Calibration procedure or to aid in checking it.
The power meter also has GPIB as do several bench meters and oscilloscopes, but that is a future project since the connectors cost a fortune.
Yes, but I was looking ahead to see if more Tx/Rx and DIP and 3v3 was practical/available
You can of course just choose to use more of the 2 x Tx/Rx 3v3 parts
jmg,
Now that you mention it there are several 3 Tx, 3 Rx devices so I could save myself a chip.
The pressure meter uses a 1/8" stereo plug.