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HARRIS
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WARNING: Disconnect and lockout AC primary power prior to servicing
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When a hardwired button is pressed, the switch momentarily applies ground to pull the
signal line low. The signal line is connected directly to the connector J4 and sent on to the
other controllers via a ribbon cable. The controller in charge of that button will
acknowledge that it received the hardwired switch signal by sending back a reply with
information that will tell the MAX 6954 to blink that particular switch. Then the
controller next determines what to do based on the current state of the transmitter. If all
is well, it will reply to the switch panel with new information that will now request it to
light that button solid. If all is not well, it will most likely turn off the LEDs to that
button.
To determine if a programmable switch has been pressed, the MAX 6954 scans the 4x8
matrix of switches. It does this by holding one of the four rows of switches at a level
‘1’, then it looks at the eight columns and stores their states into a switch register for
that particular row. After all four rows are scanned, it will repeat the scan to “debounce”
the results. It again looks at the eight columns and compares the new results to the switch
register storing the previous scan results for that row. If the compared information is not
the same, the new information is then placed into the switch register and the next scan is
performed. If they are the same information and it shows one or more of the inputs are at
a level ‘1’, it knows that particular switch or switches has been pressed. The results of
this are placed into the debounced register for that particular row. This will cause the
MAX 6954 to send an interrupt to the micro-controller. The micro-controller will then
pull the information from all 4 debounced registers and decode them to determine which
switch in that row was pressed. Once this is determined, it blinks the LEDs for that button
and then it immediately sends the information to the controller that is responsible for that
switch. The controller will then send an acknowledge packet to the switch panel micro
controller, which will process it’s information to determine the new state of the button.
Once it determines the new state of the button, it waits for a status update packet from the
switch panel and then sends the new button status. Each button status will include the
button number and the state. The switch panel micro controller will act on that
information and set the switches accordingly.
5.4.2.2 Button / Indicator Lighting
For the most part, the front panel does not light any indicators without a status from the
controller. The only exception to this is when the unit is going through a start up lamp
test.
To determine the correct lighting state of each button/indicator, the front panel will send
a status update to the controller. The front panel will send out a status update request to
a controller and wait for a reply to the request for 200 mS. If a controller replies to the
status update, it will reply with a list of data that includes all the id numbers of button/
indicators it is in charge of, and their status’. Each button/indicator id number is
decoded to determine which LEDs are associated with it, then the status of these LEDs
are set to one of 6 possible states (solid red, solid green, solid orange, blinking green,
blinking orange, or off) and that controller’s status is set to being online. If a controller
does not respond to three status requests, it’s status will be set to being offline, the status
