Campbell Scientific CR3000 CR3000 Micrologger - Page 209
CRBasic Programming
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Section 7. Installation Marks and Spaces RS‐232 signal levels are inverted logic compared to TTL. The different levels are called marks and spaces. When referenced to signal ground, the valid RS‐232 voltage level for a mark is ‐3 to ‐25, and for a space is +3 to +25 with ‐3 to + 3 defined as the transition range that contains no information. A mark is a logic 1 and negative voltage. A space is a logic 0 and positive voltage. MSB Most significant bit (the leading bit). RS‐232C Refers to the standard used to define the hardware signals and voltage levels. The CR3000 supports several options of serial logic and voltage levels including RS‐232 logic at TTL levels and TTL logic at TTL levels. RX Receive SP Space Start bit Is the bit used to indicate the beginning of data. Is the end of the data bits. The stop bit can be 1, 1.5 or 2. TX Transmit 7.8.8.5 CRBasic Programming To transmit or receive RS-232 or TTL signals, a serial port (see table CR3000 Serial Ports (p. 207) ) must be opened and configured through CRBasic with the SerialOpen() instruction. The SerialClose() instruction can be used to close the serial port. Below is practical advice regarding the use of SerialOpen() and SerialClose(). Program CRBasic example Receiving an RS-232 String (p. 215) shows the use of SerialOpen(). Consult CRBasic Editor Help for more information. SerialOpen(COMPort,BaudRate,Format,TXDelay,BufferSize) • COMPort - Refer to CRBasic Editor Help for a complete list of COM ports available for use by SerialOpen(). 209
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