Omega Vehicle Security 1400 manual Command Interpretation, Fixed Formats, Conflict Errors

Appendix A API Commands

Fixed Formats

Any Query (?)command or Status (U) command returns a fixed format. For instance, any option that can range up to 65,535 always returns five digits, so zero would be returned as 00000. In the following command descriptions, leading zeros are included. They are not, however, required when entering the command.

Conflict Errors

Some combinations of commands and parameters can be sent to the unit that are out of range for a particular configuration or inconsistent with other commands. For instance, specifying a Scan Interval (I) command to less time than the unit can acquire scans results in a conflict error:

PRINT#1,"OUTPUT07;C1-992,I00:00:00.0,00:00:00.0X"

A conflict error lights the ERROR indicator LED on the scanning unit and returns an E4 when queried with the Error Query (E?) command. Some conflict errors result in a default value for a conflicted command. For instance, in the example above, the scan interval defaults to the fastest possible scan interval for the number of defined channels.

Command Interpretation

As commands are received by the unit, they are interpreted in the order in which they are received. Some commands are immediate, which means they immediately take effect. Other commands are deferred and have no effect on device operation until the Execute (X) command is interpreted.

Immediate & Deferred Commands

The immediate and deferred commands applicable to ChartScan/1400 are listed in a table on the following page.

An example of an immediate command is Set Digital Outputs (On), which immediately chooses the digital output line which is being referred to.

An example of a deferred command is Set Data Format (F), which determines the input and output format used for channel data when X is interpreted. As deferred commands are interpreted, their desired effects are recorded in internal temporary registers. As additional deferred commands are interpreted, their effects are added to these registers, possibly overwriting earlier effects. Finally, when X is interpreted, the temporary registers are examined in the execution order described below. If two deferred commands that do not affect the same function are received before the Execute (X)command, they take effect in the execution order described below. If a deferred command is sent multiple times within a command line, the last occurrence of the command will take precedence. Note that a command line is terminated by the X. For example, if F1,1 F1,3X is sent, the data output format will be as specified by the F1,3X command. The F1,1 command is overridden and never takes effect.

If an error is detected during command processing, commands are ignored up through and including the next execute command. Thus, any immediate commands after the error, (and all deferred commands) are ignored. For example, the command line T1,1,0,0O216,0,25, 255AAT3,7 K20 X containing the error AA only executes the O0, because it is an immediate command that occurred before the error. The deferred commands T1,1,0,0 and T3,7,0,0 and the immediate command K20 after the error have no effect.

Deferred commands help reduce the effects of errors and improve synchronization of command execution. The primary advantage of deferred commands is that they are executed as a group, either all or none. If any errors occur, deferred commands have no effect and the device is left in a consistent state instead of a partially modified, inconsistent state.

ChartScan User’s Manual A-3