Hi, I am trying to make a program in C to communicate with a temperature sensor over my serial port that uses RS-485 and is a half duplex. I am however having trouble getting the device into RS-485 mode, is it possible to use RS-485 mode in Centos 6.5 or does it only support RS-232 mode?
On 11/8/2014 1:36 PM, Jason Ricles wrote:
Hi, I am trying to make a program in C to communicate with a temperature sensor over my serial port that uses RS-485 and is a half duplex. I am however having trouble getting the device into RS-485 mode, is it possible to use RS-485 mode in Centos 6.5 or does it only support RS-232 mode?
standard legacy PC serial ports are strictly RS232C. RS485 is a 120 ohm balanced line specification. What host-side serial port are you using that has RS485 support?
re: linux support, I found this: http://retis.sssup.it/~scordino/code/rs485.html which suggests '485 support is pretty thin in Linux.
I am not too sure, it is for work and we got a custom board. My co worker who is more the hardware guy set it up. I did notice it is thin before 3.0 kernal. I saw in the 3.0 kernal they have more support. So we are basically up the creek without a paddle with the device and kernal 2.6. Would a RS-485 to RS-232 converter possibly fix the problems?
On Sat, Nov 8, 2014 at 4:49 PM, John R Pierce pierce@hogranch.com wrote:
On 11/8/2014 1:36 PM, Jason Ricles wrote:
Hi, I am trying to make a program in C to communicate with a temperature sensor over my serial port that uses RS-485 and is a half duplex. I am however having trouble getting the device into RS-485 mode, is it possible to use RS-485 mode in Centos 6.5 or does it only support RS-232 mode?
standard legacy PC serial ports are strictly RS232C. RS485 is a 120 ohm balanced line specification. What host-side serial port are you using that has RS485 support?
re: linux support, I found this: http://retis.sssup.it/~ scordino/code/rs485.html which suggests '485 support is pretty thin in Linux.
-- john r pierce 37N 122W somewhere on the middle of the left coast
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
On 11/8/2014 1:55 PM, Jason Ricles wrote:
I am not too sure, it is for work and we got a custom board. My co worker who is more the hardware guy set it up. I did notice it is thin before 3.0 kernal. I saw in the 3.0 kernal they have more support. So we are basically up the creek without a paddle with the device and kernal 2.6. Would a RS-485 to RS-232 converter possibly fix the problems?
the problem is, a 232-485 converter needs to be told when to be in transmit vs recieve mode for a half duplex single pair circuit to function. as that article says, this can be done by using the RS232 RTS signal to control the RS485 line driver, but the linux driver has to know about this and support it.
Gotcha and yes that was the problem I was having, I could transmit but would just get bounced but what I transmitted due to not being able to set transmit mode. So I basically have to use
/drivers/serial/crisv10.c: serial driver used on the Cris ETRAX platform /drivers/serial/atmel_serial.c: serial driver used on Atmel platforms (AVR32 and AT91 included)
for my drivers. Sorry I am not a fully hardware guy so am a little lost at some of this stuff, but I know the software is not working since the hardware has no way to know how to interact through software.
On Sat, Nov 8, 2014 at 5:16 PM, John R Pierce pierce@hogranch.com wrote:
On 11/8/2014 1:55 PM, Jason Ricles wrote:
I am not too sure, it is for work and we got a custom board. My co worker who is more the hardware guy set it up. I did notice it is thin before 3.0 kernal. I saw in the 3.0 kernal they have more support. So we are basically up the creek without a paddle with the device and kernal 2.6. Would a RS-485 to RS-232 converter possibly fix the problems?
the problem is, a 232-485 converter needs to be told when to be in transmit vs recieve mode for a half duplex single pair circuit to function. as that article says, this can be done by using the RS232 RTS signal to control the RS485 line driver, but the linux driver has to know about this and support it.
-- john r pierce 37N 122W somewhere on the middle of the left coast
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Hi Jason,
I don't know what temperature range you want to sense. I have had success using I-Button temperature sensors directly on a USB RS232 connector. With this set up you can have multiple sensors on one line as each sensor has a unique address.
The software I used for this was from a book Linux Toys by Christopher Negus and Chuck Wolber. ISBN: 0-7645-2508-5
Regards
ChrisG
On 11/09/2014 12:21 AM, Jason Ricles wrote:
Gotcha and yes that was the problem I was having, I could transmit but would just get bounced but what I transmitted due to not being able to set transmit mode. So I basically have to use
/drivers/serial/crisv10.c: serial driver used on the Cris ETRAX platform /drivers/serial/atmel_serial.c: serial driver used on Atmel platforms (AVR32 and AT91 included)
for my drivers. Sorry I am not a fully hardware guy so am a little lost at some of this stuff, but I know the software is not working since the hardware has no way to know how to interact through software.
On Sat, Nov 8, 2014 at 5:16 PM, John R Pierce pierce@hogranch.com wrote:
On 11/8/2014 1:55 PM, Jason Ricles wrote:
I am not too sure, it is for work and we got a custom board. My co worker who is more the hardware guy set it up. I did notice it is thin before 3.0 kernal. I saw in the 3.0 kernal they have more support. So we are basically up the creek without a paddle with the device and kernal 2.6. Would a RS-485 to RS-232 converter possibly fix the problems?
the problem is, a 232-485 converter needs to be told when to be in transmit vs recieve mode for a half duplex single pair circuit to function. as that article says, this can be done by using the RS232 RTS signal to control the RS485 line driver, but the linux driver has to know about this and support it.
-- john r pierce 37N 122W somewhere on the middle of the left coast
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
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John R Pierce