Esp32 Dev Kit C Cts Rts Dtr

Posted on 09.06.2020 by admin

Esp32 Dev Kit C Cts Rts Dtr 4
Esp32 Devkit V1 Pinout

May 25, 2005 Welcome to LinuxQuestions.org, a friendly and active Linux Community. You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. May 07, 2017 Getting Started with ESP32-Bit Module and ESP32-T Development Board using Arduino core for ESP32. And it comes in kit with ESP32-bit module in one package, and ESP32-T breakout board with headers in another package. So I selected ESP32 Dev Module, and set.

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The pin numbers are often engraved in the plastic of theconnector but you may need a magnifying glass to read them.Note DCD is sometimes labeled CD. The numbering of the pins on afemale connector is read from right to left, starting with 1 in theupper right corner (instead of 1 in the upper left corner for the maleconnector as shown below). --> direction is out of PC.

Only 3 of the 9 pins have a fixed assignment: transmit, receiveand signal ground. This is fixed by the hardware and you can't changeit. But the other signal lines are controlled by software and may do(and mean) almost anything at all. However they can only be in one oftwo states: asserted (+12 volts) or negated (-12 volts). Asserted is'on' and negated is 'off'. For example, Linux software may commandthat DTR be negated and the hardware only carries out this command andputs -12 volts on the DTR pin. A modem (or other device) thatreceives this DTR signal may do various things. If a modem has beenconfigured a certain way it will hang up the telephone line when DTRis negated. In other cases it may ignore this signal or do somethingelse when DTR is negated (turned off).

It's like this for all the 6 signal lines. The hardware only sendsand receives the signals, but what action (if any) they perform is upto the Linux software and the configuration/design of devices that youconnect to the serial port. However, most pins have certain functionswhich they normally perform but this may vary with the operatingsystem and the device driver configuration. Under Linux, one maymodify the source code to make these signal lines behave differently(some people have).

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A cable from a serial port always connects to another serial port.An external modem or other device that connects to the serial port hasa serial port built into it. For modems, the cable is always straightthru: pin 2 goes to pin 2, etc. The modem is said to be DCE (DataCommunications Equipment) and the computer is said to be DTE (DataTerminal Equipment). Thus for connecting DTE-to-DCE you usestraight-thru cable. For connecting DTE-to-DTE you must use anull-modem cable (also called a crossover cable). There are many waysto wire such cable (see examples in Text-Terminal-HOWTO subsection:'Direct Cable Connection')

There are good reasons why it works this way. One reason is that thesignals are unidirectional. If pin 2 sends a signal out of it (but isunable to receive any signal) then obviously you can't connect it topin 2 of the same type of device. If you did, they would both sendout signals on the same wire to each other but neither would be ableto receive any signal. There are two ways to deal with thissituation. One way is to have a two different types of equipmentwhere pin 2 of the first type sends the signal to pin 2 of the secondtype (which receives the signal). That's the way it's done when youconnect a PC (DTE) to a modem (DCE). There's a second way to do thiswithout having two different types of equipment: Connect pin sendingpin 2 to a receiving pin 3 on same type of equipment. That's the wayit's done when you connect 2 PCs together or a PC to a terminal(DTE-to-DTE). The cable used for this is called a null-modem cablesince it connects two PCs without use of a modem. A null-modem cablemay also be called a cross-over cable since the wires between pins 2and 3 cross over each other (if you draw them on a sheet of paper).The above example is for a 25 pin connector but for a 9-pin connectorthe pin numbers 2 and 3 are just the opposite.

The serial pin designations were originally intended for connecting adumb terminal to a modem. The terminal was DTE (Data TerminalEquipment) and the modem was DCE (Data Communication Equipment).Today the PC is usually used as DTE instead of a terminal (but realterminals may still be used this way). The names of the pins are thesame on both DTE and DCE. The words: 'receive' and 'transmit' arefrom the 'point of view' of the PC (DTE). The transmit pin from thePC transmits to the 'transmit' pin of the modem (but actually themodem is receiving the data from this pin so from the point of view ofthe modem it would be a receive pin).

The serial port was originally intended to be used for connecting DTEto DCE which makes cabling simple: just use a straight-thru cable.Thus when one connects a modem one seldom needs to worry about whichpin is which. But people wanted to connect DTE to DTE (for example acomputer to a terminal) and various ways were found to do this byfabricating various types of special null-modem cables. In this casewhat pin connects to what pin becomes significant.

This is 'hardware' flow control. Flow control was previouslyexplained in the Flow Controlsubsection but the pins and voltage signals were not. Linux onlysupports RTS/CTS flow control at present (but a special driver mayexist for a specific application which supports DTR/DSR flow control).Only RTS/CTS flow control will be discussed since DTR/DSR flow controlworks the same way. To get RTS/CTS flow control one needs to eitherselect hardware flow control in an application program or use thecommand:
stty -F /dev/ttyS2 crtscts (or the like). This enables RTS/CTShardware flow control in the Linux device driver.

Then when a DTE (such as a PC) wants to stop the flow into it, itnegates RTS. Negated 'Request To Send' (-12 volts) means 'request NOTto send to me' (stop sending). When the PC is ready for more bytesit asserts RTS (+12 volts) and the flow of bytes to it resumes. Flowcontrol signals are always sent in a direction opposite to the flow ofbytes that is being controlled. DCE equipment (modems) works the sameway but sends the stop signal out the CTS pin. Thus it's RTS/CTS flowcontrol using 2 lines.

On what pins is this stop signal received? That depends on whether wehave a DCE-DTE connection or a DTE-DTE connection. For DCE-DTE it's astraight-thru connection so obviously the signal is received on a pinwith the same name as the pin it's sent out from. It's RTS-->RTS (PCto modem) and CTS<--CTS (modem to PC). For DTE-to-DTE the connectionis also easy to figure out. The RTS pin always sends and the CTS pinalways receives. Assume that we connect two PCs (PC1 and PC2)together via their serial ports. Then it's RTS(PC1)-->CTS(PC2) andCTS(PC1)<--RTS(PC2). In other words RTS and CTS cross over. Such acable (with other signals crossed over as well) is called a 'nullmodem' cable. See Cabling Between Serial Ports

What is sometimes confusing is that there is the original use of RTSwhere it means about the opposite of the previous explanation above.This original meaning is: I Request To Send to you. This request wasintended to be sent from a terminal (or computer) to a modem which, ifit decided to grant the request, would send back an asserted CTS fromits CTS pin to the CTS pin of the computer: You are Cleared To Send tome. Note that in contrast to the modern RTS/CTS bi-directional flowcontrol, this only protects the flow in one direction: from thecomputer (or terminal) to the modem. This original use appears to belittle used today on modern equipment (including modems).

The DTR and DSR Pins

Just like RTS and CTS, these pins are paired. For DTE-to-DTEconnections they are likely to cross over. There are two ways to usethese pins. One way is to use them as a substitute for RTS/CTS flowcontrol. The DTR pin is just like the RTS pin while the DSR pinbehaves like the CTS pin. Although Linux doesn't support DTR/DSR flowcontrol, it can be obtained by connecting the RTS/CTS pins at the PCto the DSR/DTR pins at the device that uses DTR/DSR flow control. DTRflow control is the same as DTR/DSR flow control but it's only one-wayand only uses the DTR pin at the device. Many text terminals and someprinters use DTR/DSR (or just DTR) flow control. In the future, Linuxmay support DTR/DSR flow control. The software has already beenwritten but it's not clear when (or if) it will incorporated into theserial driver.

The normal use of DTR and DSR (not for flow control) is as follows: Adevice asserting DTR says that its powered on and ready to operate.For a modem, the meaning of a DTR signal from the PC depends on howthe modem is configured. Negating DTR is sometimes called 'hangingup' but it doesn't always do this. One way to 'hang up' (negate DTR)is to set the baud rate to 0 using the command 'stty 0'. Trying to dothis from a 'foreign' terminal may not work due to the two-interfaceproblem. See Two interfaces at a terminal. For internal modem-serial_ports it worked OK with a portusing minicom but didn't work if the port was using wvdial. Why?