BusWorks
Model 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O
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6.0 SPECIFICATIONS
General:
Series 901/902/903MB network modules include up
to twelve digital inputs (901MB), digital outputs (902MB), or
combined input and output channels (903MB), and provide an
isolated RS485/Modbus network interface. Outputs are
open-drain, low-side switches and inputs are active-low.
Isolation is supplied between channel I/O, the network, and
power. The high-voltage, high-current outputs provide
discrete on/off control of external devices, while the non-
inverting, buffered inputs provide support for digital level
sensing or for simple readback of the outputs (903MB).
Inputs and outputs share common. Socketed I/O pullup
resistors are tied to the EXC+ terminal. This network module
is DIN-rail mounted.
The unit is configured and controlled with our user-friendly
Windows 95/98
or NT
900MB Configuration Program.
Optionally, you may use your own software as long as you
adhere to the Modbus command/response format for
supported commands. A push button on the module allows
communication with a module when its address, baud rate,
and parity settings are unknown. Non-volatile
reprogrammable memory in the module stores configuration
information.
MODEL NUMBER DEFINITION
Transmitters are color coded with a white label. The prefix
“9” denotes the Series 900, while the “MB” suffix specifies that
this device is primarily a process transmitter for Modbus
networks.
901MB:
Transmits and isolates up to 12 digital input channels.
902MB:
Transmits and isolates up to 12 digital output channels.
903MB:
Transmits and isolates up to 12 digital I/O channels.
-0900:
The four digits of this model suffix represent the
following options, respectively:
0 = No Options;
9 = Output: RS485/Modbus;
0 = Enclosure: DIN rail mount;
0 = Approvals: CE, UL, and cUL Listed.
I/O SPECIFICATIONS
Input and output circuits are connected in tandem to an I/O
terminal of the fully populated 903MB models. The same circuit
board is used to build all three models. Input circuitry is removed
for 902MB models (output only), and output circuitry is removed
for 901MB models (input only). Supported outputs are the open
drains of n-channel mosfets and intended for low-side switching
applications. Input buffers include series 100K
Ω
buffer resistors,
plus diode over-voltage clamps to +5V, and are active-low.
Transient protection is provided at each I/O terminal. Sockets for
installation of optional pullup resistor SIP’s are also provided. A
5.6K pullup resistor SIP is installed from the factory. The unit
must be properly wired and configured for the intended I/O type
(see Installation Section for details). Outputs may also be read
back via the corresponding input (903MB). The unit is easily
configured via the Modbus Configuration Program.
The following paragraphs summarize this model’s I/O types
and applicable specifications.
Digital Inputs (901MB & 903MB):
Supports up to 12 active-low,
buffered inputs, with a common connection (RTN). For DC
voltage applications only. Observe proper polarity.
Inputs include transient suppression devices and series
connected 100K
Ω
resistors, plus diode over-voltage clamps
to the in5V supply. Sockets are provided for
installation of optional SIP resistor networks to act as pullups
to the EXC+ terminal for the port. 5.6K pullup resistors are
installed from the factory. An excitation supply is typically
connected between the EXC+ and RTN terminals of the port.
Input Signal Voltage Range:
0 to +35VDC.
Input Current:
293uA, typical at 35VDC. This is computed
as the applied input voltage minus 5.7V, divided by the series
100K
Ω
input resistance.
Input Signal Threshold:
TTL compatible with 100mV of
hysteresis, typical. Low-to-High threshold is 1.7VDC typical,
High-to-Low threshold is 1.6VDC, typical. Limit logic
transition to TTL levels of 0.8VDC (Max LOW level) and
2.0VDC (Min HIGH level).
Input Resistance:
100K
Ω
, typical.
Input Hysteresis:
100mVDC typical.
Input Response Time:
800ns typical, input transition to
logic level at microcontroller. The microcontroller then
samples the inputs (as a group) approximately every 650us.
The actual input sampling rate will vary as interrupts may
occur.
Digital Outputs (902MB & 903MB Only):
Up to 12 independent,
open-drain, DMOS mosfet switches with a common source
connection at the port terminals labeled RTN. Channels are
grouped 4 to a port and include socketed pullup resistor SIP’s
to the port EXC+ terminal. A 5.6K pullup SIP resistor is
installed from the factory at each port. Outputs are for DC
voltage and current-sinking applications only, observe proper
polarity. To control higher voltages and/or currents, or for
controlling AC, an interposing relay may be used (see
Electrical Connections Drawing 4501-813). Transient
protection is built-in, but additional external protection is
recommended when switching inductive loads (see Drawing
4501-813).
Note:
When the outputs are used to control
interposing relays for switching AC and DC devices of higher
voltage/current levels, the coil ratings for the interposing relay
shall not exceed 24VDC, 100mA.
Output “OFF” Voltage Range:
0 to 35V DC. Limit voltage
to 35V or less or damage to the unit may result.
Output “OFF” Leakage Current:
:
0.1uA typical, 50uA
maximum (mosfet only, 25
°
C, 35V). Does not include the
tandem input bias current of 903MB models (see below).
Note (903MB):
The 100K
Ω
series input buffer resistors in
combination with the +5V voltage clamps at the input buffers
will tend to increase the off-state drain current with increased
drain voltage (up to 0.3mA at 35V). This is due to the fact
that the input buffer circuitry and output mosfet drain circuitry
are connected in tandem to the same I/O pin for the Model
903MB.
Output “ON” Current Range:
0 to 500mA DC, continuous
(up to 6A total for all 12 channels combined). No deration
required at elevated ambients. Group one RTN per each
group of 4 outputs.
Output R
ds
ON Resistance:
0.13
Ω
typical, 0.28
Ω
Maximum.
Output Response Time:
An output is updated within 250us
of receipt of a Force Single Coil command. For Force
Multiple Coils command, the first coil will update in about
250us, followed successively by each additional coil every
180us. For 903MB units, the output logic transition to input
logic level time is 3us typical. Actual switching time will vary
with output load and interrupts.
