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APPENDIX A

| 69

GPIO OPERATION

The pin-based GPIO protocol was designed to be easy to use with raw contact closures (or

independent logic bits). It allows a pushbutton (or toggle switch) on each pin to be useful

independently of the other buttons. For example, a processing preset may be assigned to be

selected by the “go-low” direction of each of the 5 pins in the port. If this is done and ﬁve nor-

mally-open pushbuttons are connected between the pins of a controlling GPI port and ground,

each pushbutton will select a preset when pressed. If normally-closed pushbuttons are used, the

“go-high” direction of the pins would have to be used to create the same eﬀect. One would not

typically assign both the go-low and go-high directions of the same pins at the same time. An

exception might be to use a single toggle switch on a single pin to select between 2 presets, one

for each direction. A little thought will show that using multiple toggle switches in this manner

will lead to problems selecting the desired preset without going through intermediate presets.

The following 4 GPO ports are permanently deﬁned. Their function cannot be changed.

GPO 1 -- reserved (because VOLT has no physical GPO)

GPO 2 -- preset selection

GPO 3 -- input/output routing selection

GPO 4 -- trigger script execution (not yet implemented)

As seen above, the action to take is tied directly to the port number.

The possible actions are:

Preset Selection: Each of the ﬁve pins acts independently of the others. Each pin can have one

preset assigned to a rising edge on the pin and one preset assigned to a falling edge (or “no

action” may be selected for either or both edges). Preset selection takes place only on transitions

(edges). If more than one transition takes place simultaneously, the lowest numbered pin

that has a transition will take precedence. Here, “simultaneously” means as part of the same

command to lwrd. If they are driven by physical inputs, transitions that occur within the same

sampling period will be seen as simultaneous.

Input Routing: Bits 0 and 1 select the primary input. Bit 0 acts independently to select either the

analog input on a falling edge or the AES input on the rising edge:

Lxxxx = analog input

Hxxxx = aes input

Bit 1 acts to select the LiveWire input on a falling edge. On a rising edge the simultaneously

transmitted state of bit 0 is examined to select one of the other inputs:

xLxxx = LiveWire input

lHxxx = analog input

hHxxx = aes input

If bits 0 and 1 have simultaneous transitions, bit 1 takes precedence. So LLxxx and HLxxx

switch to LiveWire.

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