DESCRIPTION AND OPERATION
DIGITAL I/O
2 - 4
WBPEEUI240755B0
®
The analog output mode jumpers set the type of output, either
current or voltage. If current mode is selected, the E/I circuits
on the I/O module convert the voltage from the D/A converter
to a current output. Refer to
in Section 3 for details.
DIGITAL I/O
The CIS and QRS modules can input three separate digital sig-
nals and output four separate digital signals. Digital inputs are
voltages of 24 VDC, 48 VDC, 125 VDC or 120 VAC. These volt-
ages indicate an energized (ON) field device; a zero volt input
indicates a de-energized (OFF) field device. The I/O module digi-
tal outputs can switch 24 VDC at 250 milliamperes or 48 VDC
at 125 milliamperes.
The I/O module has a fixed propagation (speed) of 17 millisec-
onds for DC inputs to allow for contact debounce time. Jump-
ers on the I/O module select the working voltage level and DC
or AC mode for each input. Refer to digital input jumper set-
tings
Digital Input Jumper Settings (J1, J2, J3, J4, J5, J6)
Digital Inputs
Current limiters and optocouplers in the isolation block isolate
the three field inputs from the module circuitry (Fig.
). The
threshold detection block circuits test the input voltage to
determine if it is at the proper voltage level to indicate an ener-
gized (closed) or de-energized (open) state for the field device.
These values are sent to the digital I/O buffer block. Jumpers
J1 through J6 on the I/O module select the input voltage and
input mode (DC or AC).
Digital Outputs
The output isolation block consists of optocouplers to isolate
the control logic circuits from the process (Fig.
). Four open
collector transistors that can sink a 250 mA load for 24 VDC
or a 125 mA load for 48 VDC make up the driver block.
Digital I/O Buffer
The digital I/O buffer block is a buffer and register that hold
the values of the digital inputs and outputs. The I/O expander
bus interface writes digital data to the register for output by
the driver block circuits, and reads the digital input values
from the buffer.
