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CM4

4-Ch. Serial Communications Interface and 12-Ch. Discrete I/O Function Module

The CM4 is a high-performance NAI smart Configurable Open Systems Architecture™ (COSA®) function module that integrates two critical field-proven I/O functions into a single module: Serial Communications (Comms.) and Discrete I/O. Built on NAI’s modular and scalable COSA architecture, the CM4 combines the functionality of the SC3 (Serial Comms. RS-232/422/485) and DT4 (Discrete I/O) smart modules, delivering efficient, high-density integration for aerospace and defense systems requiring avionics data interfacing and discrete signal control.

1) Serial Comms. Interface: 4 channels, fully programmable async/sync/GPIO (based on SC3)
      - 4 channel RS-232/422/485 ASYNC or GPIO / 2 channel w/ Flow Control or SYNC Comms.
2) Discrete I/O Interface: 12 channels, fully programmable as input or output (based on DT4)

Serial Communications Interface (SC3-type)
The CM4 serial communications section, based on NAI's SC3 smart function modules features 4 Channels RS-232/422/485 (ASYNC Communications or GPIO) or either 2 Channels ASYNC Communications w/ Flow Control (RTS/CTS) or 2 Channels SYNC Communications (Clocked). The SC3-type functionality is highly versatile, making it ideal for multi-protocol communication applications.

Discrete I/O (DT4-type)
The CM4 Discrete I/O section, based on NAI’s DT4 smart function module (the enhanced version) features 12 programmable channels for either input (voltage or contact sensing with programmable, on-module pull-up/pull down current sources), or output (current source, sink, or push-pull) up to 500 mA per channel from an applied, external 5 – 60 VCC source. These modules can sense broken input connections and whether an input is shorted to +VCC or to ground. Additional enhanced features are listed below

CM4_product_image-min.png
CM4_product_image-min.png
Technical Help
Specifications
  • Serial Communications (RS-232/422/485): see below
  • Number of Channels/Types: Four (4) RS-232, RS-422, RS-485, non-isolated.
  • Data Rate (SC Mode): RS422 and RS-485: 1.5 Mbit/s ASYNC or 10 Mbps SYNC; RS-232 ASYNC or SYNC: 250 Kbps for each channel in serial communications mode.; Data rate will be within 1% of commanded rate. Data can be read 4 μs after receipt in UART (typical bus transfer). These data rates are verified with all channels running simultaneously.
  • Data Transfer (SC Mode): Data transfers within 300 ns, no latency issues.
  • Receive/Transmit Buffers (SC Mode): 1MB x 16 Receive and Transmit buffers.
  • Mode of Operation: RS-232: Single Ended, RS-422: Discrete, RS-485: Discrete
  • Number of Drivers & Receivers on one-line max typ.: RS-232: 1 driver and 1 receiver, RS-422: 1 driver and 10 receivers, RS-485: 32 drivers/receiver pairs.
  • Maximum Data Rate: RS-232: 250 kb/s, RS-422: 1 Mb/s, async or 10 Mb/s sync, RS-485: 1 Mb/s async
  • Driver Output Signal Level (Min Loaded): RS-232: ±5 V @ 3kΩ load, RS-422: ±2 V @ 100Ω load, RS-485: ±1.5 V @ 54Ω load
  • Driver Load Impedance (Ohms): RS-232: 3k (min.), RS-422: 100, RS-485: 54
  • Max. Driver Current in High-Z State (Power On): RS-232: N/A, RS-422: N/A, RS-485: ±100 μA
  • Max. Driver Current in High-Z State (Power Off): RS-232: ±6 mA @ ±2 V, RS-422: ±100 μA, RS-485: 100 μA
  • Receiver Input Voltage Range: RS-232: ±15 V, RS-422: -10 V to +10 V, RS-485: -7 V to +12 V
  • Receiver Input Sensitivity: RS-232: ±3 V, RS-422: ±200 mV RS-485: ±200 mV
  • Receiver Input Resistance (Typ.) (Ohms): RS-232: 5k (3k to 7k), RS-422: 125k (1/8 unit load) 120 (term enabled), RS-485: 125k (1/8 unit load) 120 (term enabled)
  • :
  • Discrete I/O: see below
  • Input Range: 0 to 60 VDC. Programmable for either voltage or switch closure sensing. Noted: External VCC required for current source (high side drive) or input pull-up (5 mA max) for OPEN/GND contact sense (applied per bank of 6 Ch.).
  • Overvoltage Surge Protection: 80 VDC max. (< 50 ms); 100 VDC max. (< 1 μs)
  • Voltage/Contact Sensing: Software selectable per bank. When the input channel is utilized for direct voltage sense, Vcc is not required. When input is used to detect switch closures, Vcc is required to provide a current source (pull-up). Vcc per channel bank must be between 5 VDC min. and 60 VDC max. This module has 2 Vcc banks, each with 6 channels for a total of 12 channels/module.
  • Input Pulse Detection: A pulse of greater than 20 μs minimum width will be sensed and reported by the appropriate High–Low or Low-High transition status/interrupt.
  • Input Impedance:: 1 MΩ (with or without power applied to module).
  • Switching Threshold: Four levels (High, Low, Short to +V, Short to ground) are programmable from 0 to 60 VDC with 10-bit resolution.
  • Voltage Measurement: Users can read the input voltage of each channel. From: LSB=100 mV. Accuracy: ±3 LSB’s (300 mV) over temp. to: 1% FSR
  • HIGH/LOW Differential (Hysteresis): 300 mV min. recommended. Programmable by using Upper & Lower thresholds.
  • Debounce: Programmable per channel from 0x00000000 (deactivated) to 0xFFFFFFFF (2^32 * 10μs) LSB= 10 μs; 32-bit resolution.
  • Update Rate: Each channel is updated every 10 μs.
  • Additional Enhanced Input Mode Operation: Pulse Measurements, Transition Timestamps, Transition Counters, Period Measurement and Frequency Measurement.
  • Output Formats: Low-Side (current sink), High-Side (current source) or Push-Pull (current source-sink); programmable per channel.
  • Output Voltage Range: 0 to 60 VDC (Output voltage is defined by the user provided Vcc applied to channel bank). Low-side drive does not require Vcc. High-side and push-pull drive requires Vcc.
  • Overvoltage Surge Protection: 80 VDC max. (< 50 ms); 100 VDC max. (< 1 μs)
  • Output Current: 0.5 A maximum (28 V Vcc typical) per channel; 2 A total per Vcc bank (total Module capacity 4 A); Measurement accuracy: ±10% ± 25 mA
  • Output Impedance: < 1 Ω (0.5 Ω typical)
  • Current Share Applications: 0.5 A maximum (28 V Vcc typical) per channel. 2 A total per Vcc bank (total Module capacity 4 A). Each channel can be programmed to generate frequency, pulse or arbitrary pulse width with 10 microsecond minimum resolution. Short circuit protected.
  • Overcurrent Protection: Low current (average): > 625 mA average over 3 ms; High current (pulse): > 6 A for less than or equal to 30 μs
  • Additional Enhanced Output Mode Operation: PWM Output and Pattern Generator Output. 64 KB allocated for Pattern Generator.
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  • General: see below
  • Power*: 5 VDC @ 250 mA (375 mA fully loaded w/ 54 Ω load per SCx channel est.). Does not include DT external VCC. * Pending design verifications and qualification.
  • Weight: 1.75 oz. (50 g)
Block Diagram
CM4_block_diagram_1200x800.png
Documentation
CM4 Data Sheet
7/16/2025 8:03:12 AM
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NAI’s Configurable Open Systems Architecture™ (COSA®) offers a choice of over 100 smart I/O, communication, and Ethernet switch functions, providing the highest package density and greatest flexibility of any multifunction I/O board in the industry. Preexisting, fully-tested functions can be combined quickly and easily in an unlimited number of ways. Choose the ideal platform for your application below. Each I/O function has dedicated processing, unburdening the system Single Board Computer (SBC) from unnecessary data management overhead.

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