Setra System Model 470 - Manual (Page 7)

7
SECTION THREE
Communications Interfacing
3.1 Communications Software Protocols
The Setra 470 RS-232 communication port allows several rates of data transfer (baud rates)
between the Setra 470 and the host device. Both devices must communicate at the same data
rate.
The factory default baud rate of the Setra 470 is 2400. Therefore, the device connected to the
Setra 470 initially must also be set to 2400. To change the Setra 470 baud rate refer to Section
5.2.
The Setra 470 transmits data as a series of standard ASCII characters, formulated by carriage
return and line feed characters. No software or hardware handshaking or error checking proto-
cols are used. Each character of data is represented in a specific format:
1 start bit
8 data bits
1 stop bit
no parity
Most computers, terminals and data acquisition systems used as hosts for the
Setra 470 allow adjustment of the format used to represent the characters of data. Adjust the
format of the host to match that of the Setra 470 in order to allow the devices to communicate.
The Setra 470 ignores carriage returns, line feeds, blank spaces and all other characters which
are not command characters listed in the summary in Section 3.4.
3.2 Executing a Function
You may execute all of the functions of the Setra 470 by transmitting the appropriate command
from the host to the transducer through the RS-232 interface. The commands are standard
alphabetic characters that correspond to the functions described in this manual, and are transmit-
ted in ASCII code.
Read the detailed explanations of the functions you want to execute in the following sections of
the manual before beginning.
The table in Section 3.4, summarizes the functions and characters which the 470 recognizes, and
the character commands for each. For the convenience of some software programmers, the
decimal and hexadecimal ASCII values of the command characters are also listed.
To execute a function, transmit the appropriate character code from a terminal or computer. For
example, to interrogate the transducer for a pressure reading, transmit the letter P, for PRINT, to
the transducer. The transducer reports data back to the computer.
Details of this and all other functions are included in following sections of the manual.
3.3 Clearing a Number or Function
To clear a number or function that is partially or incorrectly transmitted, transmit C, for CLEAR.
This clears the previously transmitted data without affecting any other functions which may be in
use.
To reset the Setra 470 to its power up condition, transmit - C, (the minus symbol followed by C).
This clears the ZERO/tare value, shuts off MIN/MAX and CONVERTs back to the original engi-
neering units of pressure. All of these functions are described in later sections of this guide.