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CMH

5-Ch. Serial ASYNC Communications Interface and 6-Ch. Differential I/O

The CMH Function Module is a compact, high-performance solution that integrates two essential I/O functions into a single smart function module: Serial communications and Differential I/O. This module leverages NAI’s advanced Serial RS-232/422/485 Communications (SC3) and Differential I/O (DF1) smart function module technologies, providing exceptional versatility and integration for aerospace and defense applications that require both serial data communication and differential signal I/O processing.

5-Channel Serial Communications (Based on SC3 Functionality)
- 1 channel RS-232 ASYNC with flow control (TX/RX/CTS/RTS)
- 4 channels RS-422/485 ASYNC (TX±/RX±)

6-Channel Differential RS-422/485 I/O (based on DF1 functionality)

Serial Communications Interface
The CMH smart combination serial communications (SC3-type) function section provides 5 fully programmable serial communication interface channels, supporting 1 RS-232 channel and 4 RS-422/485 channels. The SC3-type functionality is highly versatile, making it ideal for multi-protocol communication applications.

Differential I/O Interface
The CMH smart combination Differential I/O (DF1-type) function section provides 6 fully programmable differential I/O channels, configurable as either input or output. These channels ensure reliable signal transmission and reception in high-noise environments, making them ideal for control and feedback in aerospace and defense systems.

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Technical Help
Specifications
  • Serial Communications (RS-232/422/485): see below
  • Number of Channel Types: One (1) RS-232 and four (4) RS-422, RS-485, non-isolated.
  • Data Rate (SC Mode): RS-422 and RS-485: 1.5 Mbit/s for each channel in asynchronous differential mode (burst). RS-232: 250 KB/s. 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: Differential, RS-485: Differential
  • 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-422/485: 1.5 Mb/s, async
  • Driver Output Signal Level (Min Loaded): RS-232: ±5 V @ 3 kΩ load, RS-422: ±2 V @ 100 Ω load, RS-485: ±1.5 V @ 54 Ω 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)
  • Differential I/O (Input): see below
  • Operational Mode: RS-422, RS-485
  • Receiver Input Levels: RS-422: -10 V to 10 V, RS-485: -7 V to 12 V
  • Receiver Input Sensitivity: RS-422: ±200 mV, RS-485: ±200 mV
  • Receiver Input Resistance: RS-422: 120 Ω / 125 kΩ, RS-485: 125 kΩ (Each channel incorporates a 120 Ω termination resistor that can be programmed on a channel by channel basis.)
  • Read Delay: RS-422: 300 ns (100 ns with low EMI off), RS-485: 300 ns (100 ns with low EMI off)
  • Debounce: RS-422: Programmable per bit from 0 to 34.36 sec. (LSB = 8 ns) (pending characterization), RS-485: Programmable per bit from 0 to 34.36 sec. (LSB = 8 ns) (pending characterization)
  • :
  • Differential I/O (Output): see below
  • Driver Output Voltage: RS-422: -0.25 V to +5 V max., RS-485: -0.25 V to +5 V max.
  • Driver Output Signal Level (Loaded Minimum): RS-422: ±2 V, RS-485: ±1.5 V
  • Driver Output Signal Level (Unloaded Maximum): RS-422: ±5 V, RS-485: ±5 V
  • Driver Load Impedance (Maximum Driver Current IN): RS-422: 100 Ω, RS-485: 54 Ω
  • Hi-Z State (Power-On) (Maximum Driver Current IN): RS-422: N/A, RS-485: ±100 µA
  • Hi-Z State (Power-Off): RS-422: ±10 µA, RS-485: ±10 µA
  • Write Delay: RS-422: 100 ns, RS-485: 100 ns (low EMI off)
  • Protection: Short circuit protected, thermal shutdown, built-in current limiting.
  • Rise/Fall Time: 31 ns into a 50 pf load
  • :
  • General: see below
  • Power*: 5 VDC @ 220 mA, 360 mA fully loaded (54 Ω load per SCx channel). *Pending design verification and qualification.
  • Weight: 1.75 oz. (50 g)
Block Diagram
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Documentation
CMH Data Sheet
5/16/2025 8:14:35 AM
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