Hello,
Are there any switching device or Application for switching CAN - RS232?
Please see the attached picture.
I serarched digital logic device, mux device in website, but I can't find the device which we can use it.
Best Regards,
Ryuji Asaka
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Hello,
Are there any switching device or Application for switching CAN - RS232?
Please see the attached picture.
I serarched digital logic device, mux device in website, but I can't find the device which we can use it.
Best Regards,
Ryuji Asaka
Hello Ryuji,
There is a TI reference design for a multi protocol RS-485/RS-232 transceiver system which can be found here:
This design is fairly simple, basically the FORCEOFF pins on the RS-232 transceivers are tied together and used to switch the device into RS-485 mode and likewise, the DE and RE pins on the RS-485 transceivers are toggled to switch the device back and forth between modes. For this design the modes are toggled with a simple jumper as seen on the schematic:
It should be relatively simple to extend this basic idea to a RS-232/CAN switching device. For example, using a CAN device with the "Silent Mode" feature, the CAN transceiver could be placed into listen-only mode while the RS-232 communication is taking place on the bus line. The above circuit could be modified to allow mode control via the CPU rather than by jumper. The SN65HVD1050 is an example of a CAN device with this Silent Mode feature.
On thing to note about this strategy is that the receiver for the CAN device would be enabled during RS-232 communication. This may or not be an issue depending on your application. If your design uses two separate TX and RX lines in the TTL section as shown in your diagram, then the CAN receive line could simply be ignored during RS-232 communication. If they operate on the same TX and RX lines, then there could be an issue of interference between the RX lines of two devices. More details about the application could help to determine if this is a viable option for you.
Best Regards,
Casey McCrea
Hello Ryuji,
The standby mode of the SN65HVDA540-Q1 may cause issues vs. silent mode because in standby mode, the bus lines are weakly biased to ground. Silent mode will put the bus outputs in a high impedance state which will ensure that the CAN device doesn't interfere with operation of the RS-232 device.
As for the CD4055B-Q1, Ron may be able to give you more insight.
Best Regards,
Casey
Ryuji san,
CD4055B is not Q1. It is a CMOS BCD-to-7-Segment LCD Decoder/Driver with Display-Frequency Output. Was there a different device in mind?
I believe the logic device recommendation did not consider a negative -13V signal.
Ron,
I suspected this would be ok if one of the CAN lines was pulled 5k ohms to GND but I did some testing in the lab to confirm. As expected, the recessive level will be pulled down towards ground, but the driver is still able to establish a valid dominant level on the bus with no problems. I tested both situations, CANH pulled to GND and CANL pulled to ground, and found no issues with sending/receiving data. I tested data rates from 100kbps to 1Mbps with the SN65HVD1050.
Best Regards,
Casey