A Communications with a Computer

Application

The Model 8718B can be connected to a computer for real time transmission of data via the meter’s RS232 connector. A limited number of the meter’s functions can also be controlled remotely via the RS232 bus.

Checksum and Modulo Description

Modulo 256 is the remainder of any number X divided by 256. As an example, if the checksum is 1234, Modulo 256 of 1234 is 210. The two ASCII digits to be transmitted as the checksum would be D and 2 (the decimal-hex conversion of 210). An equivalent calculation is to convert the sum to Hex and transmit the two lowest digits. The Hex of 1234 is 4D2, therefore the digits to transmit are ASCII D and 2.

Computer to Model 8718B Message Format

The first character in any message is the “>”. This allows the Model 8718B to synchronize to the computer. Upon detection of the “>” character, the 8718B will:

•Set itself to a listen mode, thereby eliminating the possibility of a bus contention problem.

•Reset its character counter to allow storage of succeeding characters in an internal buffer.

The next characters(s) is selected from the functions listed in Command Character Function table.

Appendix A Communications with a Computer

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