Question:  

Do you ever find that SEND_LEVEL does not behave as expected - it just doesn't send the level when you think it should?

Symptoms and Causes:

SEND_LEVEL is a "smart" command.  The master tracks the last level value sent and won't send it again.  This is actually a feature - it allows a programmer to put a naked SEND_LEVEL in your code without having to track whether it's changed or not.

For example, you can write:

DEFINE_PROGRAM SEND_LEVEL <device>,<level>,<value>

Instead of:

DEFINE_PROGRAM

IF (<new value> <> <old value>)

{

<old value> = <new value>

SEND_LEVEL <device>,<level>,<new value>

}

In Axcess, the master tracks what was sent by line number - each SEND_LEVEL statement is tracked separately.  If you have a number of SEND_LEVELs throughout your code, they just may not work because at each specific SEND_LEVEL, the same value was sent as the last time on that particular line.

In NetLinx, the master's device manager tracks what was last sent to a particular level on a device.  This allows a bit more flexibility.

Resolution:

In Axcess systems, it is critical that:

1. The Device parameter must not be a variable.
2. The Level parameter must not be a variable.
3. The Value parameter MUST be a variable.

In addition, it is highly recommended that you have only one SEND_LEVEL in your program for each device, level pair.  This will be in your DEFINE_PROGRAM section.

​For example:

DEFINE_DEVICE

VOL = 96 (* volume device *)

TP = 128 (* touch panel device *)

DEFINE_VARIABLE

TP_L1 (* variable to store touch panel level 1 *)

DEFINE_START

(* tell master to store touch panel level 1 in TP_L1 *)

CREATE_LEVEL TP, 1, TP_L1

DEFINE_PROGRAM

(* send level from tp level 1 to vol levels 1 & 2 *)

SEND_LEVEL VOL, 1, TP_L1

SEND_LEVEL VOL, 2, TP_L1

(* end *)

While it is not as critical to program this way in NetLinx, you still need to be aware that if you have sent a particular value to a particular DEVLEV, a send level that sends that same value again will not work until a different level value is sent to the DEVLEV, or until the device goes off-line, and the master realizes the level has reset to 0 (and you're not sending a value of 0).