Technical information

DRV Operator’s Manual and Technical Reference (rev 1 0 June 30, 2000)

state the logic gate input, which is high impedance and considered infinite for this

purpose, is high. The input state is changed when the logic gate input changes to low.

Therefore, switching it to ground changes the input. When the external switch is closed

and the input is grounded, the pull up resistor limits the current and results in a +5 VDC

drop. The voltage at the logic gate input is now the same as the ground reference, 0 VDC

potential difference to ground. Figure B.1 illustrates a basic TTL filtered input with a

pull up resistor.

+ 5 VDC

LOGIC GATE

INPUT

(High Im peadance)

INPUTS

BASIC TRANSISTOR-TRANSISTOR LOGIC (TTL) INPUT

Pull up resistor

Figure B.1

The potential difference referenced to ground should be nominally +5 VDC at any of the

digital inputs when the external switches are in an open position. When the switches are

closed, the inputs should be 0 VDC. The signal can also be checked at the switch. With

the switch in the open position there should be +5 VDC across the switch. With the

switch in the closed position, the potential difference across the switch and referenced to

ground should both be 0. If the inputs behave as described above they are working

properly. If there is +5 VDC present but the switch does not drive the input to zero then

there is a problem external to the controller. The problem may be wiring, termination, or

the switch itself.

B.1.3 Digital Outputs

The digital outputs control the indicator lamps and the output relays. Both the relays and

indicator lamps are supplied with a constant +12 VDC and switched, via the controller, to

ground. The digital outputs of the controller are open collector. An open collector output

works by sinking current. The load is supplied with a constant positive voltage with the

ground- side connected to the controller output. The output is switched to ground via the

internal output transistor.

Warning !!!