RS-485 - Revision history

JulienB: /* Links */

2022-04-01T16:41:54Z

‎Links

JulienB: /* Supported Board and Software versions */

2017-12-04T13:42:07Z

‎Supported Board and Software versions

JulienB at 11:56, 1 December 2017

2017-12-01T11:56:05Z

JulienB: /* Hardware Notes */

2017-12-01T11:54:58Z

‎Hardware Notes

JulienB: /* Hardware Notes */

2017-11-27T11:32:34Z

‎Hardware Notes

JulienB: /* Supported Board and Software versions */

2017-11-27T11:31:06Z

‎Supported Board and Software versions

JulienB: /* Supported Board and Software versions */

2017-11-27T11:29:58Z

‎Supported Board and Software versions

JulienB: /* Hardware Notes */

2017-11-15T14:31:32Z

‎Hardware Notes

JulienB: /* How to use it from C code */

2017-11-15T14:30:05Z

‎How to use it from C code

JulienB: /* Changing port parameters */

2017-11-15T14:29:22Z

‎Changing port parameters

@@ Line 104: / Line 104: @@
 ==Links==
 * De-asserting RTS fastest as possible is a well known problem on every platforms:
 ** https://blog.savoirfairelinux.com/en-ca/2013/adding-rs-485-support-to-the-beaglebone-with-short-turnaround-delay/
 [[Category:Serial ports]]

@@ Line 10: / Line 10: @@
 * Use the latest Armadeus GIT/SF repository or the latest stable release.
 * Currently tested only on the [[APF28]] (i.MX28) board with Linux kernel 2.6.35 (patch 462) and 4.9 (patch 703). If device tree is used, you need to activate rts/cts on UART used for RS-485.
-* Busybox ''stty'' command requires a patch included in Armadeus BSP.
+* Busybox ''stty'' command requires a patch included in Armadeus BSP, to handle specifics RS-485 parameters handling.
 == Changing port parameters ==

← Older revision		Revision as of 11:56, 1 December 2017
Line 106:		Line 106:
	* De-asserting RTS fastest as possible is a well known problem on every platforms:		* De-asserting RTS fastest as possible is a well known problem on every platforms:
	** https://blog.savoirfairelinux.com/en-ca/2013/adding-rs-485-support-to-the-beaglebone-with-short-turnaround-delay/		** https://blog.savoirfairelinux.com/en-ca/2013/adding-rs-485-support-to-the-beaglebone-with-short-turnaround-delay/
		+
		+	[[Category:Serial ports]]

← Older revision		Revision as of 11:54, 1 December 2017
Line 102:		Line 102:
	* The TXEN/RTS output is _active low_, it must be inverted to use it with the popular RS-485 transceiver ICs. On kernel with device tree, this can be done with ''rs485-rts-active-high'' option when declaring UART config.		* The TXEN/RTS output is _active low_, it must be inverted to use it with the popular RS-485 transceiver ICs. On kernel with device tree, this can be done with ''rs485-rts-active-high'' option when declaring UART config.
	* When U-Boot runs and the board start to boot, the RTS pin works as an input, so please add a pull-up resistor to this pin, before the inverter, to prevent RS-485 bus lockups.		* When U-Boot runs and the board start to boot, the RTS pin works as an input, so please add a pull-up resistor to this pin, before the inverter, to prevent RS-485 bus lockups.
		+
		+	==Links==
		+	* De-asserting RTS fastest as possible is a well known problem on every platforms:
		+	** https://blog.savoirfairelinux.com/en-ca/2013/adding-rs-485-support-to-the-beaglebone-with-short-turnaround-delay/

@@ Line 100: / Line 100: @@
 == Hardware Notes ==
 * The RS-485 Transmit Enable (TXEN) output will be the RTS pin of the UART.
-* The TXEN/RTS output is _active low_, it must be inverted to use it with the popular RS-485 transceiver ICs.
+* The TXEN/RTS output is _active low_, it must be inverted to use it with the popular RS-485 transceiver ICs. On kernel with device tree, this can be done with ''rs485-rts-active-high'' option when declaring UART config.
 * When U-Boot runs and the board start to boot, the RTS pin works as an input, so please add a pull-up resistor to this pin, before the inverter, to prevent RS-485 bus lockups.

@@ Line 9: / Line 9: @@
 == Supported Board and Software versions ==
 * Use the latest Armadeus GIT/SF repository or the latest stable release.
-* Currently only the [[APF28]] (i.MX28) board with Linux kernel v2.6.35.3 supported. (mxs-auart patch)
+* Currently tested only on the [[APF28]] (i.MX28) board with Linux kernel 2.6.35 (patch 462) and 4.9 (patch 703).
-* Linux stty patch included in Buildroot 2012.02 to only busybox v1.19.4
+* Busybox ''stty'' command requires a patch included in Armadeus BSP.
-* Linux stty patch included in Buildroot 2013.05 to all busybox versions starting from v1.19.4
 == Changing port parameters ==

@@ Line 49: / Line 49: @@
 == How to use it from C code ==
-* The RS-485 mode can be turned on with ioctl calls from C code, here is the example:
+* The RS-485 mode can also be turned on with ioctl calls from C code, here is the example:
 <source lang="C">
 #include <stdio.h>

@@ Line 16: / Line 16: @@
 * Setup APF28 serial port for RS-485 communication:
 <pre class=apf>
-# stty -F /dev/ttySP0 9600
+# export SERIAL_DEV=/dev/ttySP0
-# stty -F /dev/ttySP0 raw
+# stty -F $SERIAL_DEV 9600
-# stty -F /dev/ttySP0 -echo -echoe -echok
+# stty -F $SERIAL_DEV raw
-# stty -F /dev/ttySP0 rs485
+# stty -F $SERIAL_DEV -echo -echoe -echok
 </pre>
 * Set extra delays (if needed) for TXEN/RTS signaling before and after the transmitted packet (in microseconds):
 <pre class=apf>
-# stty -F /dev/ttySP0 rs485delaybefore 100
+# stty -F $SERIAL_DEV rs485delaybefore 100
-# stty -F /dev/ttySP0 rs485delayafter 100
+# stty -F $SERIAL_DEV rs485delayafter 100
 </pre>
-* To get current RS-485 parameters. (If the port device supports the RS-485 options you will see the last two lines)
+* To get current RS-485 parameters: (if the serial port supports the RS-485 options, you will see previous rs485 parameters values)
 <pre class=apf>
 # stty -F /dev/ttySP0
@@ Line 41: / Line 42: @@
 Please note:
 * You can't set the "rs485delaylastchartx" parameter, it's calculated automatically from the baudrate.
-Special notes for the APF28/iMX28 mxs-auart driver:
+Special notes for the APF28/i.MX28 ''mxs-auart'' driver:
 * All delays are in microseconds.
 * The "rs485delaylastchartx" parameter is not used in DMA mode.
 * The parameters: "rs485rtsonsend" "rs485rtsaftersend" "rs485rxduringtx" are not used. (Only used by atmel_serial.c and crisv10.c drivers)
-* If the RS-485 mode is turned on, it will override (turn off) the RTS/CTS hardware flow settings of the uart, don't care what is configured.
+* If the RS-485 mode is turned on, it will override (turn off) the RTS/CTS hardware flow settings of the UART, whatever is configured.
 == How to use it from C code ==