Dynapro Technologies Dynapro ET TCS, Application Developer'S Manual

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Serial data can be transmitted in either a synchronous or asynchronous timing format. In a
synchronous format, individual codes in the message are synchronized to a clock signal and sent
one after another, without any special bits separating them. Start and stop codes mark the
beginning and end of each message block, but start and stop bits are not sent with each code.
In an asynchronous format, transmitted data is not synchronized to a clock. Instead, start and stop
bits mark the beginning and end of each code. Asynchronous formats have the advantage that the
sender and receiver do not need to be synchronized with each other. The TCS uses an
asynchronous format only.
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Serial data speed is expressed in bits per second, or baud. Although baud technically means the
number of state changes per second (which is not always equal to bits per second), the term baud
rate is usually used interchangeably with bit rate. The TCS can send and receive data at all the
following bit rates: 110, 300,600, 1200, 2400, 4800, 9600, and 19200 baud.
The TCS sends and receives data at the same rate. For example, the TCS cannot be set to
transmit data at 9600 baud and receive data at 1200 baud.
The baud rate is selected by the user through the Setup Screen. Instructions for selecting the baud
rate are provided in the Installation Guide, under the heading, Using the Setup Screen.
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Each code sent between the TCS and the host is preceded by one start bit, a space (binary zero).
The start bit is immediately followed by seven or eight data bits, the code itself. The data bits are
followed by an optional parity bit, and finally one or two stop bits, which are marks (binary
ones).
The combination of all the serial bits is called the framing format. Table 2-1 shows all framing
formats supported by the TCS. Figure 2-1 shows the framing format to transmit a code using
seven data bits, a parity bit, and two stop bits.
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