altered. Sequential locations will contain values from previous measurements.

TRANSPARENT MODE

The SDI-12 transparent mode is used to communicate directly with a SDI-12 sensor. A common application of the transparent mode is to verify proper SDI-12 sensor operation.

A computer or terminal is required to use the transparent mode; the CR10KD (keyboard display) cannot be used. Transparent mode is entered while the computer is in telecommunications with the SDI-12 recorder CR10 (at the asterisk '*' prompt). Enter 'pX' at the asterisk prompt, where 'p' is the Control Port number (1-8) attached to the SDI-12 data line. The CR10 responds with a '<' prompt. Any SDI-12 command preceded with the sensor address and followed with an exclamation point '!' may then be entered. For example, entering '0I!' at the '<' prompt would request identification from a SDI-12 sensor addressed at 0.

The '<' prompt will not appear until the recorder CR10 finishes executing all program tables. While in transparent mode, scheduled tables in the recorder CR10 will not execute. Transparent mode ends when a response is received and displayed, if no response is received from the SDI-12 sensor within the time-out period following a valid command (approximately 1/3 second), or if the user does not enter a command before the mode times out (approximately 35 seconds). Security must be unlocked to level 2 before the Transparent mode is used.

*** 106 SDI-12 SENSOR ***

Instruction 106 allows a CR10 to be used as a SDI-12 sensor. The CR10 can make measurements and transfer data using SDI-12 commands in response to another SDI-12 recorder. Instruction 106 is only in standard PROM OSI0-1.1.

Instruction 106 supports the standard SDI-12 commands as listed in the Parameter 2 description for Instruction 105.

The SDI-12 data line is attached to Control Port 8 and Instruction 106 must be the first instruction in Subroutine 98 located in Table 3.

SECTION 9. INPUT/OUTPUT INSTRUCTIONS

ASDI-12 recorder addresses the SDI-12 sensor CR10 by sending a Break and the sensor's address. The sensor CR10 will call subroutine 98 whenever it detects activity on the SDI-12 data line attached to Port 8, but if the Break and the specified address are not received by Instruction 106, the remainder of the subroutine is not executed.

Two programming techniques exist for obtaining measurement values to be transferred by the sensor Instruction 106. The first technique makes the requested measurements "on demand" in response to the recorders request. The measurement instructions are located in Subroutine 98 and are executed only when the SDI-12 recorder requests measurements. This technique is preferred when measurements are to be made at the recorder's command.

The second technique transfers measurement values previously obtained by instructions in Table 1 or Table 2. Subroutine 98 contains only Instructions 106 (SDI-12 sensor) and 95 (End). When the recorder requests measurements, values already in the specified input locations are used. The advantage of this technique is that the sensor CR10 can be making and storing measurements independent of the SDI-12 recorder. The data is also returned slightly faster since the sensor CR10 does not make measurements when the recorder requests data, but rather uses measurements made at the last regular table execution.

These two techniques can be combined allowing the sensor CR10 to function as a SDI-12 sensor and to make independent measurements. While Subroutine 98 is being executed, normal Table 1 or 2 execution scheduling may be altered or missed since Subroutine 98 is not interrupted. This is likely to occur if Subroutine 98 execution takes longer than the scan interval programmed for Table 1 or 2. It is also possible for instructions in Table 1 or 2 to prevent Subroutine 98 from being called in time for Instruction 106 to receive the address information from the recorder. This is likely to occur only if Table 1 or 2 is executed often and has instructions that take longer than 1/3 second to execute. For example, Instruction 4 (Excite- Delay-SE) with a 1/2 second delay could cause Subroutine 98 to miss the SDI-12 address information if it were executing when the SDI-12

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