Chapter 10 Interfacing and Vision Systems 245
Serial Ports
Serial transmission delivers digital data over long distances, but at a
fairly slow rate. The transmission rate is slow because data must be trans-
mitted one bit at a time. Two computers can communicate with each other
over telephone circuits via serial ports connected to modems. Existing
transmission lines can be used, which is an advantage.
A common serial interface used in robotics is the standard RS-232C.
RS-232C was developed to standardize the interface between data terminal
equipment and data communications equipment. This interface is most
commonly used when binary data is transmitted over short distances, such
as between two computers or between a computer and a piece of peripheral
equipment. The circuit performs three functions: data transfer, timing, and
control (Figure 10-5).
AA 1 Protective ground X
AB 7 Signal ground/common return X
BA 2 Transmitted data X
BB 3 Received data X
CA 4 Request to send X
CB 5 Clear to send X
CC 6 Data set ready X
CD 20 Data terminal ready X
CE 22 Ring indicator X
CF 8 Received line signal detector X
CG 21 Signal quality detector X
CH 23 Data signal rate selector (DTE) X
CI 23 Data signal rate selector (DCE) X
DA 24 Transmitter signal element
timing (DTE) X
DB 15 Transmitter signal element
timing (DCE) X
DD 17 Receiver signal element
timing (DCE) X
SBA 14 Secondary transmitted data X
SBB 16 Secondary received data X
SCA 19 Secondary request to send X
SCB 13 Secondary clear to send X
SCF 12 Secondary received line signal
detector X
Pin Assignments and Interchange Circuit Functions
Ground Data Control Timing
Interchange
Circuit
Pin
Number
Description From
DCE
From
DCE
From
DCE
To
DCE
To
DCE
To
DCE
Figure 10-5. This chart lists pin assignments and interchange circuit functions for the RS-232C serial
interface standard.