Sink/Source Inputs.
Almost all DC inputs in GE PLCs can be
used for either sink or source. We have used them only for sink. See the next note on
Sinking inputs for a schematic and more details.
Sink Inputs.
Each input is basically a resistor with one end
of each resistor tied to individual terminals. The other ends are tied together to a
terminal marked "Com". This pull down resistance sinks voltage and current to
common VDC.
The output on the MSP is designed to be used as either sink or
source. The MSP contains a sinking gate and pull-up resistor. Sink inputs can be wired
directly to the MSP.
Make sure that the PLC input module and MSP input get their 24 VDC
from the same source. Following is a schematic of a typical input. "%I?" may be
any valid input. In the single channel drivers for the 90 MICRO the input is %I1 but may
be changed if desired. In the multiplexed drivers for the 90 MICRO Channel 0 and 1 are %I1
and %I2 respectively but may be changed if desired.

Source Inputs.
Each input is basically a resistor with one
end of each resistor tied to individual terminals. The other ends are tied together to a
terminal that is tied to COM. This pull up resistance sources voltage and current from
+VDC.
The output on the MSP is designed to be used as either sink or
source. The MSP contains a sinking gate and pull-up resistor. Source inputs can be wired
directly to the MSP.
Using the input as source would increase the level of the signal
and make it more immune to noise but it would double the current required when the signal
is pulled to zero volts.
Make sure that the PLC input module and MSP input get their 24 VDC
from the same source. Following is a schematic of a typical input. "%I?" may be
any valid input.
Note: The true/false sense for a sourcing input is opposite
that of a sinking input. In ladder logic the hardware input into the driver must be
negated to provide the proper logic sense.

Relay Outputs.
Relay outputs can be used as either sink or
source. We have used them only for source. See the next note on Sourcing outputs for a
schematic and more details. Until recently the 90 MICRO had only mechanical relay outputs
so we had to slow the output driver down in order to debug it and not destroy the relay. I
used a scan time of 30 msec for the MSP analog output modules.
Output on Demand.
In order to conserve the life of the relay
output the output drivers contain some extra logic that allows control of when the output
is transmitted. There are two bits for the user to access for this control.
The first bit "Out Demand Continuous" when turned on will
cause the output to transmit continuously. When this bit is turned off the driver will
complete the current transmission and then will remaining off. The continuous transmission
bit has been forced on by ladder logic by default but may be edited if desired.
The second bit "Out Demand Single" causes the output to
transmit one time. Only the off to on transition of this bit will cause a transmission.
The continuous transmission bit takes priority over the single transmission bit. The
continuous transmission bit must be turned off in order to use the single transmission
bit. It is recommended that if the single transmission bit is use that the Delta Refresh
Count Preset be set to zero (0). When the Delta Refresh Count Preset is set to zero (0)
the full 16 bit value will be transited every time and the delta transmission is
effectively turned off.
Input/Output Scan Time Ratio.
For those drivers using both
inputs and outputs there is logic that runs the output a factor of 3 times slower than the
input. This allows the input to run at a scan time of 10 msec and the output to run a scan
time of 30 msec. This is necessary only when relay outputs must be used.
Source Outputs.
Each output is basically a transistor or gate
with one end of each transistor tied to individual terminals. The other ends are tied
together to a terminal that is usually labeled COM. This pull up transistor sources
voltage and current from +VDC.
The input on the MSP is sink; it is basically a resistor tied to
-VDC or common. Source outputs can be wired directly to the MSP.
Make sure that the PLC output module and MSP output get their 24
VDC from the same source. Following is a schematic of a typical output. "%Q?"
may be any valid output. In the single channel drivers the output is %Q 1 but may be
changed if desired. In the multiplexed drivers Channel 0 and 1 are %Q 1 and %Q 2
respectively but may be changed if desired.

Sink Outputs.
Each output is basically a transistor or gate
with one end of each transistor tied to individual terminals. The other ends are tied
together to a terminal that is usually labeled COM VDC. This pull down transistor sinks
voltage and current to COM VDC.