I have a root shell given by sudo bash. cs5 cs6 cs7 cs8 : Select character size in bits (cs7 most common. c. $ stty -F /dev/ttymxc2 crtscts and disable flow control with $ stty -F /dev/ttymxc2 -crtscts To view the current settings for UART3, use $ stty -a -F /dev/ttymxc2 Just replace /dev/ttymxc2 with the name of the UART device. init 1200 cs7 -parodd parenb -cstopb -icanon -iexten -ixon -ixoff -crtscts cread clocal echo -echoe echok -echoctl. We are using GPIO 8/9/10/11 for UART4 incl. sean-mcmanus changed the title CRTSCTS from termios. Feb 4, 2016 at 6:31. Instead of changing to a very fast baudrate (that cannot detect any framing), change to a moderate 38400 baud or a slower 4800 baud, either of which should cause reception/display of garbage characters. com, ddrokosov@salutedevices. FT232RL is FTDI and has good support for windows drivers. ) CS8 : 8N1 (8bit, no parity, 1 stopbit) CLOCAL : Local connection. 2 Apr 22 2021 - 23:19:25. Odd parity, else even. I've tried to export TERM with: linux, xterm, xterm-color, xterm-256color, ansi, screen-256color,. The Linux version of getty. $ stty 19200 cs8 -parenb crtscts -echo -F /dev/ttyS0. Avoid repeating the same code for rs485 twice. It was once very common that a Unix installation involved one server machine and many "dumb" character mode terminals or dial-up modems. Using PPP across a null modem (direct serial) connection. Whenever the UART finds a 0x0A in the datastream it adds 0x0D with it and transmitting. Press the Ctrl-J key sequence before and after the command instead of the Enter key. Parity enable. Enter another number: Status: -1. [requires _BSD_SOURCE or _SVID_SOURCE] c_lflag flag constants: ISIG When any of the characters INTR, QUIT, SUSP, or DSUSP are received, generate the corresponding signal. probonopd commented on Feb 7, 2015. If you check the specs of the UART you'll probably find that it takes some small amount of time to set up after you set the options. 今回は、ioctl()の第2,第3引数の正体とioctlの使い方について説明します。 まずはioctl()の引数について。crtscts (不属于 posix) 启用 rts/cts (硬件) 流控制。 c_lflag 标志常量： isig 当接受到字符 intr, quit, susp, 或 dsusp 时，产生相应的信号。 icanon 启用标准模式 (canonical mode)。允许使用特殊字符 eof, eol, eol2, erase, kill, lnext, reprint, status, 和 werase，以及按. • HW flow control enable with the crtscts option • The scripts for connect and disconnect • Other options depending on usage . 250416E-14A,+8. From: <[email protected]. 2 netmask 255. h: No such file or directory I thoughtcrtscts (-crtscts) RTS/CTS フロー制御を有効 (無効) にします。 入力モード: これは termios 構造体の c_iflag に相当します。 ignbrk (-ignbrk) 入力のブレーク信号を無視します (無視しません)。 brkint (-brkint)Hi, This is the friendly patch-bot of Greg Kroah-Hartman. Q&A for work. c_cflag &= ~(CSIZE | PARENB | CRTSCTS); Previous Next. If the CRTSCTS flag is clear, the state of CTS has no effect. Thanks. In Linux, you can find so many different applications to build a L2TP server. This allows the UART to be used for ter- minals, modems and serial line IP applications. CRTSCTS (not in POSIX) Enable RTS/CTS (hardware) flow control. Uart0 is used as RS232 (RTS/CTS) and Uart1 as RS485 (RTS controlling driver): 8 ps7_uart_0: uartps@e0000000 {. Would anyone be able to help me with this?+1. However while running, it reminded that autoConnect could not connect after drvAsynSerialPortConfigure was executed. first with “ GitHub - cbrake/linux-serial-test: Linux Serial Test Application ” enable rtscts control uart can transmit but no voltage change on rts and cts pin. The full source code is listed as follows:I use Code blocks 20. 100. print all current settings in a stty-readable form. Program Examples. 99 as the host with ppp0). microcom -s 115200 /dev/ttyPS1. After that, CTS/RTS became effective. I am trying to run a Roland MDX-20 milling machine using a Raspberry Pi. Then, CTS/RTS was not effective, and I have been worried for a long time. Configured minicom to use hardware flow control (Ctl A-O to open minicom serial port setup menu, and F to enable hardware flow control). kernel. org> Subject: FAILED: patch "[PATCH] tty: serial: meson: fix hard LOCKUP on crtscts mode" failed to apply to 5. ICANON Enable canonical mode. The problem you are facing is a correct behaviour. 5. Enter another number: 3. 3. The configuration file is composed of sections and [email protected]) is a follows: # define CRTSCTS 020000000000 This flag is used in the struct termios. crtscts. You can find the rest described in the. My termios setup is modifying the first character read from the serial port using read (). See Setting Terminal Modes Properly. I've followed the readme guide, I've looked into the troubleshooting steps, and nothing seems to help. I have changed the kernel boot parameters console and androidboot. But this has no effect on the relevant pin. Set the HCI device into raw mode (the kernel and bluetoothd will ignore it). The following one just set the termios c_cflag to the CRTSCTS value: crtscts Specifies that pppd should set the serial port to use hardware flow control using the RTS and CTS sig‐ disconnect script Execute the command specified by script, by passing it to a shell, after pppd has terminated the link. – user2430607. print all current settings in a stty-readable form. The most common setting here is to disable it. -F, --file = DEVICE. 4. Sign up for free to join this conversation on GitHub . 4. Some did solve it by using the command "stty --file=/dev/ttyUSB0 crtscts -hupcl", and are pretending they have to send the command from the python script, in order to have the serial port working. (시리얼 케이블이 모든 핀에 연결되어 있는 경우만 사용하도록 한다. a. cstopb -cstopb: Use two (one stop bits per character. I have oscilloscope traces I can share next week. Then, CTS/RTS was not effective, and I have been worried for a long time. I typically use screen (1) to open a serial port with the command: sudo screen /dev/ttyUSB2 115200. org Cc: <[email protected] stops code evaluation and posting #4131. crtscts mru 576 mtu 576 passive 10. c","contentType":"file. 0. The termios. hup -hup; speed nnnn Saved searches Use saved searches to filter your results more quickly >> CRTSCTS constant will be defined. Enter another number: ^C. 2. bytesize = serial. See the comments in the code for explanation of the use of the different input modes. Per the man pages this does the following:Use the readyRead () signal to get notified when new data is available in the device instead of looping forever. UART can write, but can not read in Linux on Zynq. org, neil. EIGHTBITS ser. Edit (or create, if it doesn't exist) ~/. h is squiggled with 'identifier "CRTSCTS" is undefined' but it can compile on gcc without any problems Default cStandard is incorrectly c11 instead of. There are at least two compilation errors below. Then without exiting the communications program (such as minicom) see if the device driver knows about. h file. But I have found, that: * even if flow control is switched off, serial_core. 串口通过termios进行配置。. Xilinx Zynq MP First Stage Boot Loader. 14-stable. 2．数据位. returns Code: speed 1200 baud; 0 rows; 0 columns; lflags: -icanon isig -iexten echo -echoe echok echoke -echonl -echoctl -echoprt -altwerase -noflsh -tostop. The most common setting here is to disable it. No prompt appears for approximately 40. 255. crtscts stands for a Control setting to use the RTS and CTS pins of the serial port for hardware flow control. 0 to TTL UART 6PIN CP2102 Module Serial Converter to connect my Leonardo to my Fedora29 box. Hi, I would like to use modem control signals (RTS/CTS) in my ZYNQ MIO peripherals, but I'm not sure about how to enable these features in my embedded design. From: Pavel Krasavin <pkrasavin@imaqliq. Printcap with serial/crtscts device. This option is not implemented on Windows. Here is some environment information: $ gcc --version $ gcc (Ubuntu 4. `ixon' Enable XON/XOFF flow control (that is, `CTRL-S'/`CTRL-Q'). write() is working properly as I am able to send data to uart and read it from my laptop which is connected to pixhawk using a FTDI cable to telem2. Check the specific port driver manual page to see if hardware flow control is supported on the port you are using. You use whatever ad-hoc "standard" your equipment implements. 16. 7 of Serial-HOWTO) CS8 : 8n1 (8bit,no parity,1 stopbit) CLOCAL : local connection, no modem contol CREAD : enable receiving characters */ newtio. c_cflag &= ~(CSIZE | CSTOPB | PARENB | CRTSCTS Previous Next. crtscts: A Boolean indicating whether to use hardware flow control (RTS/CTS signals). Specifies that pppd should set the serial port to use hardware flow control using the RTS and CTS signals in the RS-232 interface. When working with ttyUSB, it is necessary to adjust the speed of the converter to the one with which the device is working behind the USB <-> UART converter. with Creative Commons CC-BY-SA. Version-Release number of selected component (if applicable): 1. I've looked through the Arduino's Serial software websites, but none of them seemed to have a clear explanation or just no explanation at all how to program the serial communication. sample. I have tried to set the correct serial settings using. [requires _BSD_SOURCE or _SVID_SOURCE] c_lflag flag constants: ISIG. 1:192. g. init. Each section has a given name which will be used when using the configuration FIFO (normaly /var/run/l2tp-control). Saved searches Use saved searches to filter your results more quickly This assumes that sizeof (int) == 4 is true, adjust for other sizes as needed, the problem remains. 長いオプションに必須の引数は短いオプションにも必須です。. Resolution. RTS and CTS are not necessary. Setting up the PPP options files. Bug Type: TypeScript Environment Vue Version: 3. This is very simple - there is no modem in the way so things are much simpler. Mandatory arguments to long options are mandatory for short options too. sudo stty -F /dev/ttyS0 -a. 45 Element Plus Version: 2. This tutorial shows you how to use PARODD . Re: How to enable CTS RTS for Raspberry Pi 3 b+ UART. log proxyarp connect-delay 5000 refuse-pap refuse-chap refuse-mschap require-mschap-v2 #Windows连接必须设置. . Example 4-2. 端末設定の表示、または変更を行います。. 0. stty -echo. However, the CRTSCTS flag is missing. Which is a XY question and most probably is not what [he] really wants - to implement reading from the file descriptor in a separate thread with buffering (i. CREAD : 문자 수신을 가능하게 한다. I am assuming either I have some of the termios flags set incorrectly, or the write command set. If you're not using RTS/CTS, there's also the ixon setting that enables XON/XOFF flow control, but you may not want that. One common reason to modify termios settings is to read a password without echoing characters. For example, to view information that comes from the device behind the converter, you can use a command of the form: screen /dev/ttyUSB0 115200. */The Belkin F5U109 seems to be a device of fairly old design, so perhaps the F5U409 with the same usb vendor:device id is similar. {"payload":{"allShortcutsEnabled":false,"fileTree":{"uart_example_linux/src":{"items":[{"name":"main. If neither the crtscts, the nocrtscts, the cdtrcts nor the nocdtrcts option is given, the hardware flow control setting for the serial port is left unchanged. crtscts (posix にはない) rts/cts (ハードウェア) フロー制御を有効にする。 [_bsd_source か _svid_source が必要] c_lflag フラグは以下の通り: isig intr, quit, susp, dsusp の文字を受信した時、対応するシグナルを 発生させる。 icanon カノニカルモードを有効にする (下記参照. com, gregkh@linuxfoundation. 1. I don’t want hardware control, I want software control. Some serial ports (such as Macintosh serial. Introduction. --help. "stty crtscts" kills modem. CRTSCTS : 하드웨어 흐름 제어. RS232 +12V -12V is not TTL, avoid TTL devices these are for microcontrollers etc. Just based on the names, RTS/CTS would seem to be a natural fit. Facing similar issue. 2. After removing it,. But then we are back to my original problem, how to autorun this without knowing if my device (/dev/ttyMarantz) exists or not? As before, it would be nice if socat were run by the udev rule, when the port is set up, but. I have also ruled out any code issues. PC ( usually, DTE device): PC_UART_CTS ----INPUT; PC_UART_RTS---OUTPUT. Description. All works fine expect the commissioning with the Thread Commissioning App. (Default is 5 seconds. 13. the code compiles and works ok under solaris8 (both sparc and x86). c_cflag |= CREAD | CS8 | HUPCL | CLOCAL | CRTSCTS; The full source code is listed as follows:17. I have confirmed that when sending a character from Linux on the Zynq-7035, out the /dev. Note that this means that you can get a single or double echo (or no echo at all. Check our new training course. This means that the compiler never sees the strings CONSTANT_1 and CONSTANT_2 but instead gets the source in a preprocessed form with these macros replaced with their expansions ( 1 and 2 respectively). h and in asm/termbits. There are multiple ways of doing things because there were never any protocols built into the standards. hupcl -hupcl, Stop asserting modem control (do not stop) asserting modem control on last close. c_cflag = B9600 | CRTSCTS | CS8 | CLOCAL | CREAD; /* IGNPAR : ignore bytes with parity. Put the read in a loop, perhaps with a short delay between calls based on the setup time of UART. 11 2. To get 9600 bps 8N1 with no flow control: Examples. Gentoo's Bugzilla – Bug 99556 Unable to compile gtkterm - CRTSCTS undeclared Last modified: 2005-07-31 20:25:39 UTC node [vulture]II:busybox stty -F /dev/ttymxc3 raw ispeed 9600 ospeed 9600 cs8 -ignpar -cstopb -echo -crtscts <--無法作loopback . The kernel input buffer is about one page or 4KB, so your application has to get well behind with. h instead of termios. The persist option will keep pppd alive in case of a disconnect or when it can't connect in the first place. I have verified that the cable is not too long, and the USB dongle is OK. However, as you have pointed out, when the screen command is executed, the echo attribute of the selected serial port (in this case /dev/ttyS0) reverts to. The c_lflag field of the argument structure is used by the line discipline to control terminal functions. py:368it works good, good version of the controller, good FBuffer Length, When i read the buffer, the file begin by the correct magic word (0xFF 0xD8) but doesn't end with the correct one (0xFF 0xD9) which is strange because the file size it coherent with the annouced FBuffer size. Whencontrol (CRTSCTS) and to assert/deassert RTS via ioctl. This is almost never what. 8. But /dev/ttyS* ports are full-duplex, with CRTSCTS or without, > so they don't use such handshaking. 3. Enabling this when it should be disabled can result in your serial port receiving no data, as the sender will buffer it indefinitely, waiting for you to be “ready”. 99 as the host with ppp1). # stty -a speed 38400 baud; rows 59; columns 208; line = 0; intr = ^C;QNX Momentics IDE User's Guide. The problem you are facing is a correct behaviour. UTF-8 all works fine. If you're not using RTS/CTS, there's also the ixon setting that enables XON/XOFF flow control, but you may not want that. Read more about it here. One can use the TIOCMGET ioctl () to check the pin state, but then we need to send one byte at a time, which makes it. lecture materialsLinuxのC言語でシリアル通信に使うtermios構造体のc_cflag変数についてメモ。 数値はもしかしたら環境依存です。後に示すプログラムを実行して確認しました。 名前 値 説明 CBAUD 0x0000100F ボーレートのマスク。値は※1 CSIZE 0x00000030 データ長のマスク。値は※2 CSTO…patch to fix this. Aaron Liao 這裡我們探討 Linux 序列埠程式設計，你需要熟悉 C 語言和 Linux。. I am trying to run a Roland MDX-20 milling machine using a Raspberry Pi. Readline is a library that allows line editing and other things like tab completion. On most systems with termios, you can set the CRTSCTS flag in the ->c_cflags member of the termios structure that you pass to tcsetattr, and have the kernel or hardware do the RTS/CTS flow control for you. or for old stty versions < 1. Open a terminal in Linux and type picocom -b 115200 /dev/ttyUSB0. writing the same thing over and over, yet to different people), I was. Problems encountered: The serial port is configured in the MTK chip, and crtscts is enabled. 16. kernel. If neither the crtscts, the nocrtscts, the cdtrcts nor the nocdtrcts option is given, the hardware flow control setting for the serial port is left unchanged. 1 and the other end of the link will be 10. petalinux is using 2019. Parity enable. CRTSCTS : output hardware flow control (only used if the cable has all necessary lines. MX6 to that of PC. The output will look like that shown in Example 4-2. The state of the FIFOs, modem signals, and other controller functions are read using the status, interrupt Linux C 配置串口. I have a serial device set to raw mode with stty -F /dev/ttyS0 raw. Preprocessor macros do not have "scope" as such, they just define a piece of text that should replace the macro in the code. -g, --save. sudo stty -F /dev/ttyS0 -a. The termios functions describe a general terminal interface that is provided to control asynchronous communications ports. 0. Serial Devices and the login: Prompt. c:38: error: `CRTSCTS' undeclared (first use in this function) >> >> CRTSCTS is defined in bits/termios. This is however false: > tty. To be able to output the value I use the following code using termios libraries:I want to read data from UART, i followed this tutorial, the write function works as expected, however i'am getting problem with the read function : This is the uart_init function: void uart_init(). h> or <posix1_lim. I have tried to set the correct serial settings using. 6. Tag Description-a, --all: print all current settings in human-readable form -g, --save: print all current settings in a stty-readable form -F, --file=DEVICE: open and use the specified DEVICE instead of stdinSaved searches Use saved searches to filter your results more quicklysystem February 20, 2013, 6:09pm 1. second i test with command “sudo /sbin/getty -L 9600 ttyTHS1 -h” -h mean enable flow control. serial stty CommandsFor instance, STTY=crtscts enables outbound hardware flow control. The basic line discipline. The suspended (tty output) means that the background task attempted to read input from the terminal, and was stopped with SIGTTYOUT. I set: sudo chmod o+rw /dev/ttyUSB0 stty -F /dev/ttyUSB0 1. h RWAP. exclusive: A Boolean indicating whether to open the device exclusively. 1 -chap modem #noauth -pap persist #maxfail 0 #holdoff 10 The passive option limits the number of (re)connection attempts. c asserts RTS during opening the serial device. 要修改数据位可以通过修改termios结构体. 28. hupcl -hupcl, Stop asserting modem control (do not stop) asserting modem control on last close. One common reason to modify termios settings is to read a password without echoing characters. There is a misconception that the serial ports/buses are slower than parallel ports/buses as the transmission of data is only a bit per unit of time. xl2tpd (前略) #crtscts (中略) #lock (中略 末尾に追加) name xl2tpd refuse-pap refuse-chap refuse-mschap require-mschap-v2 persist logfile /var/log. We can set the CRTSCTS by "stty -F /dev/ttyS0 crtscts" 3、I have some question 1) Does the qemu init all pci-serial port crtscts or raw? For example, I make the qemu configure with 4 pci-serial port. The current sum is: 5. sudo raspi-config. stty -F /dev/tty0 1000000 raw clocal -hupcl -echoIn the mode, CTS is INPUT, RTS is OUTPUT. 0. Asking for help, clarification, or responding to other answers. If that doesn't work try shift + backspace / del. microcom -s 115200 /dev/ttyPS1. The CRT can’t enforce a CRT order for you, or help you file with a court for enforcement. To get 9600 bps 8N1 with. Sometime delete works as backspace. copy : Ctrl + c. You can use strace to diagnose and chat -v should show all characters received. Get to know Eclipse; What's new in the IDE? Starting the IDE; Preparing your target; Creating a target connection crtscts -crtscts: Enable (disable RTS/CTS flow control. 如何获取该结构呢？. This sort of thing is managed by the readline library whose behavior can be controlled via ~/. System administration command. 8 for more details. Linux The following serial port programming and those components 1. 2. STTY accepts all the stty modes. > > Tested on S905X3 based board. mossheim mentioned this issue on Dec 1, 2018. UART adding 0x0d with 0x0a in the datastream. 2. org Cc: <stable@vger. However most of them have an infra-red interface and this tutorial describes how you can read it using a. Then, we just set up our script. Those boards are based on chips FT232RL CH340G CP2102 and others. The UART may not be configured to use them. armstrong@linaro. It is only available for those Unix versions that support POSIX termios style tty I/O control configured during installation. Local Modes. The low level driver is also responsible for handling interrupts for the port, and providing any console support. termioslib is a simple no-nonsense wrapper for UNIX termios. uart 通信のテストをする c のプログラムです。. In this case, using XON/XOFF flow control is aCRTSCTS on, CRTSXOFF on. See sect. -a, --all. pppd persist crtscts auth +chap 10. 3. Get to know Eclipse; What's new in the IDE? Starting the IDE; Preparing your target; Creating a target connectioncrtscts -crtscts: Enable (disable RTS/CTS flow control. qemu not support serial hardware flow control stty command is used to manipulate the terminal settings. I understand that the normal way to use this device is to download the driver for your favorite OS, install it, and then it's plug-and-play. dmbaturin renamed this task from xl2tp does not use kernel modules to Use kernel mode L2TP in xl2tpd. This will write the desired data on to the serial port. Code: Select allThere might be hard lockup if we set crtscts mode on port without RTS/CTS configured: # stty -F /dev/ttyAML6 crtscts; echo 1 > /dev/ttyAML6; echo 2 > /dev/ttyAML6Foot Notes. Computer1 -> USB-Serial Converter -> Serial Cable -> Serial port of Computer 2. The cool thing is, if I send "stty -F /dev/ttyACM0 -cstopb -crtscts cs8 9600 ; echo "ver" >>/dev/ttyACM0" when I open a "screen /dev/ttyACM0" the version value is sitting there, so I know Im talking to it, but it cant. dmbaturin closed this task as Resolved. ignbrk (-ignbrk) Ignore (do not ignore) break on input. cs5 cs6 cs7 cs8 : Select character size in bits (cs7 most common. Make it obvious we clear CRTSCTS bit in termios->c_cflag whenever sport->have_rtscts is false. A "modem disconnect" apparently involves toggling the RTS line, because once that flag is disabled, the behavior goes away regardless of the CRTSCTS flag setting. 0. // enable the nonblocking mode for reading. This is what I've done, and it seems working for now. org, neil. h: No such file or directory. If not, then there maybe a flow control issue. 3. 1. The modem control lines TIOCM_CAR, TIOCM_CTS, TIOCM_RTS, TIOCM_DSR and TIOCM_DTR are provided for the serial ports, although the TIOCMGET ioctl() call will not return the state of the TIOCM_RTS or. > CRTSCTS constant will be defined. Get a virtual cloud desktop with the Linux distro that you want in less than five minutes with Shells! With over 10 pre-installed distros to choose from, the worry-free installation life is here! Whether you are a digital nomad or just looking for flexibility, Shells can put your Linux machine on the device that you want to [email protected]. 2 Crux. xl2tpd: unrecognized option 'crtscts' The crtscts option seems to come from ppp-options. Using the command stty -F /dev/ttyS1 -a I can confirm that crtscts has been enabled. Try entering : stty sane. {"payload":{"allShortcutsEnabled":false,"fileTree":{"":{"items":[{"name":"LICENSES","path":"LICENSES","contentType":"directory"},{"name":". Example of this issue when I attempt to output command history: albert@t450:/$ history 1 sudo rasp-config 2 sudo raspi-config 3 sudo nano /boot/cmdline. SOL2. Availability: Unix. CRTSCTS and dialin. For example, if I am tail -f ing a file or read ing user input, <Enter> will produce ^M in the terminal instead of ending the read or adding a newline to stdout. CRTSCTS (not in POSIX) Enable RTS/CTS (hardware) flow control. 83. 128 as the client) to the main server (192. $ vi / etc / ppp / options _____ auth crtscts lock hide-password modem mru 296 mtu 296 lcp-echo-interval 30 lcp-echo-failure 4 noipx persist asyncmap 0xa0000 mru 1500 refuse-chap ipcp-max-failure 30 logfile / home / root / ppp In my case we use the PAP authentication file (may vary depending on Network Provider). ( Prolific PL-2303 HXD USB to RS-232 Serial Adaptor. cstopb -cstopb: Use two (one stop bits per character. Low Level Serial Hardware Driver ¶. I have a serial device that has no flow control, but is powered from the RS232 port by holding the RTS high and DTR low. 串口通信参数指的是波特率、数据位、奇偶校验位和停止位。. You probably do need c_cflag &= ~CSTOPB and c_cflag &= ~CRTSCTS which got removed! Either of these could kill reading. CRTSCTS. c_lflag 的. 0. RTS is an output from the UART IP block so it must be routed to a CTS pin. Similarly, it looks for low on its CTS (nCTS) signal before sending data. Yesterday, after enabling the FCM of 0xFF000024 directly with the devmem command, stty -F /dev/ttyPS1 crtscts. c_cflag to indicate that RTS/CTS flow control should be used. 7 of Serial-HOWTO) CS8 : 8n1 (8bit,no parity,1 stopbit) CLOCAL : local connection, no modem contol CREAD : enable receiving characters */ newtio. The command is probably best issued from the rc. For a complete description of these calls, see termios (3) Unix manual page. to it: echo "READ?" > /dev/ttyUSB0. No other pins are plugged in. Then when a DTE (such as a PC) wants to stop the flow into it, it negates RTS.