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The 80x86 IBM PC and Compatible Computers- P12

The 80x86 IBM PC and Compatible Computers- P12: Praised by experts for its clarity and topical breadth, this visually appealing, one-stop source on PCs uses an easy-to-understand, step-by-step approach to teaching the fundamentals of 80x86 assembly language programming and PC architecture. Offering users a fun, hands-on learning experience, it uses the Debug utility to show what action the instruction performs, then provides a sample program to show its application. | DTE - DCE Connection DTE - DTE Connection Figure 17-7. DTE-DCE and DTE-DTE Connections Some of the pins of the RS-232 are used for handshaking signals. They are described below. They are so widely used that understanding them is essential in the study of any UART chip. 1. DTR data terminal ready . When the terminal or a PC COM port is turned on after going through a self-test it sends out signal DTR to indicate that it is ready for communication. If there is something wrong with the COM port this signal will not be activated. This is an active-low signal and can be used to inform the modem that the computer is alive and kicking. This is an output pin from DTE PC COM port and an input to the modem. 2. DSR data set ready . When a DCE modem is turned on and has gone through the self-test it asserts DSR to indicate that it is ready to communicate. Therefore it is an output from the modem DCE and input to the PC DTE . This is an active-low signal. If for any reason the modem cannot make a connection to the telephone this signal remains inactive indicating to the PC or terminal that it cannot accept or send data. 3. RTS request to send . When the DTE device such as a PC has a byte to transmit it asserts RTS to signal the modem that it has a byte of data to transmit. RTS is an active-low output from the DTE and an input to the modem. 4. Cl S clear to send . In response to RTS when the modem has room for storing the data it is to receive it sends out signal CTS to the DTE PC to indicate that it can receive the data now. This input signal to DTE is used by DTE to start transmission. 5. CD carrier detect or DCD data carrier detect . The modem asserts signal CDC to inform the DTE PC that a valid carrier has been detected and that contact between it and the other modem is established. Therefore CDC is an output from the modem and an input to the PC DTE . 6. RI ring indicator . An output from the modem DCE and an input to a PC DTE indicates that the telephone is ringing. It .