New-Tech Europe Magazine | June 2019

Signal Name

Mnemonic Function

Turned on by the DTE when it is ready to transmit data. This line must be on before the DCE can turn on DSR.

Data Terminal Ready

DTR

Data Set Ready

DSR

Turned on by the DCE to indicate that the DCE is online.

Carrier Detect Ring Indicator Request To Send

DCD

Turned on by the DCE when it is receiving a carrier from a remote DCE.

RI

Turned on by the DCE when remote telephone line is ringing.

RTS

Turned on by the DTE when it is ready to send data.

Turned on by the DCE in response to a received RTS command. Held on until RTS is turned off and the last data bit is received.

Clear To Send

CTS

Receive data.

Receive Data Line

R

X

Transmit data.

Transmit Data Line

T

X

Table 1: The RS-232 control and handshake signals. (Table source: Digi-Key Electronics)

conversion and feeds both sections of the dual UART. Each section has independent control lines. The TL16C752D operates from supply voltages of from 1.8 volts to 5.5 volts over a temperature range of from -40°C to 85°C.

transmit FIFOs capable of data rates up to 3 megabits per second (Mbits/s) (Figure 3). Each section of the UART has its own software-controlled baud rate generator. The data bus interface performs the parallel-to-serial data

handshaking is implemented using the following actions: 1. The data terminal equipment pulls the RTS line down to the “1” or “Mark” state 2. The data communications equipment pulls the CTS line into the “1” or “Mark” state 3. The data terminal equipment pulls the Data Terminal Ready (DTR) line to the “1” or “Mark” state for the duration of the data transfer 4. At the end of the transfer the data terminal equipment restores the DTR and RTS lines to the “0” or “Space” state 5. The data communications equipment restores the CTS line to the “0” or “Space” state RS-232 can also use a software handshake to control data flow where the XON (ASCII DC1, hex 11) and XOFF (ASCII DC3, hex 13) characters, sent in the data stream, perform a similar synchronization of transferred data. UART functional block diagram The Texas Instruments TL16C752D is a dual UART with 64-byte receive and

Figure 3: The functional block diagram of the 3 Mbit/s Texas Instruments TL16C752D dual UART shows the 64-byte FIFOs and interface lines. (Image source: Texas Instruments)

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