What is the null modem connection?
A null modem serial cable (frequently called a crossover cable) is used to connect two DTE devices together without the use of a DCE device in between. For this to happen, the Transmit (TXD) and Receive (RXD) pins on one of the serial connectors are flipped.
What does a null modem adapter do?
Null modem cables changed that old standard, allowing devices to be linked up directly with no middleman equipment. This allows older computers and other machines with serial ports to transfer data between each other directly, similar to more modern ethernet crossover cables.
How do I know if my cable modem is null?
To tell if your NI serial cable is null modem or straight though, search for its part number in NI Serial Hardware Specifications and Features and note the cable type in the description. Alternatively, you can use a handheld DMM to test continuity on the individual pins of your serial cable.
Is RS485 single ended?
RS-422/RS-485 is used because of its single-ended nature and the full-duplex scheme of the RS-232 serial data transmission.
What is the null modem connection Mcq?
Explanation: In null modem connection the RxD of one is the TxD for the other. Explanation: SCON register is mainly used for programming the start bits, stop bits and data bits of framing. As it consists of bits like RB8, TB8, SM0, SM1, SM2 etc. 10.
How many minimum wires are needed for a null modem cable?
Direct Serial Connections (DTE to DTE) There are several classes of null modem cables, each with many variations: Minimum 3- or 4-Wire Cable. In this cable, RD and TD are cross connected and Signal Ground goes straight though (and optionally also Frame Ground).
Is null modem cable straight through?
A null modem cable is a RS-232 serial cable where the transmit and receive lines are crosslinked. In some cables there are also handshake lines crosslinked. In many situations a straight-through serial cable is used, together with a null modem adapter. The adapter contains the necessary crosslinks between the signals.
Does RS485 need termination?
Both ends must be terminated since the direction of propagation is bidirectional. In case of an RS485 twisted pair cable this termination is typically between 120 and 130 Ω. Here is a simple schematic of how the end of the lines should be terminated: “RT” is the 120 Ω termination resistor.
Why is a serial port called Serial MCQs?
Explanation: In the isochronous mode of transmission, each bit of the data is sent per each cycle. Explanation: The serial port is used to connect the keyboard and other devices which input or output one bit at a time.
What should be done if you want to double the baud rate?
With the fixed crystal frequency, baud rate could be doubled by making SMOD – 1. When the SMOD bit is set to 1, 1/12 of XTAL is divided by 16 (instead of 32) and that is the frequency used by Timer 1 to set the baud rate.
Is serial port male or female?
Generally, serial port connectors are gendered, only allowing connectors to mate with a connector of the opposite gender. With D-subminiature connectors, the male connectors have protruding pins, and female connectors have corresponding round sockets.
What makes a null modem a null cable?
Null modem cables are serial cables that use an alternative pinout for different functionality. A standard DB9 AT cable pinout (non-null modem) Originally, all serial cables were AT cables and could not connect two devices (such as two computers) directly. They required a modem or similar equipment as a go-between.
Do you need a null modem for a DB9 cable?
A standard DB9 AT cable pinout (non-null modem) Originally, all serial cables were AT cables and could not connect two devices (such as two computers) directly. They required a modem or similar equipment as a go-between. Null modem cables changed that old standard, allowing devices to be linked up directly with no middleman equipment.
What was the original purpose of the RS-232 modem?
Originally, the RS-232 standard was developed and used for teleprinter machines which could communicate with each other over phone lines. Each teleprinter would be physically connected to its modem via an RS-232 connection and the modems could call each other to establish a remote connection between the teleprinters.
Can a null modem be used as a handshake?
With a null modem connection the transmit and receive lines are crosslinked. Depending on the purpose, sometimes also one or more handshake lines are crosslinked.