C Series modules connect to the CompactRIO controller through a 15-pin D-SUB connector. The communication, power, and ground signals in this connection are available for your custom design. An ID EEPROM is required to store identification information. You also can use the EEPROM for module-specific calibration data. The I/O circuitry implements the primary functionality of the module.
The module interface supports two modes of communication between the CompactRIO controller and individual modules: ID mode and operation mode. ID mode is required and used to access the ID EEPROM on the module. As noted, the ID EEPROM contains information about the module, such as the vendor ID, product ID, and serial number. NI requires that you use a default vendor ID as described in the module development kit user manual if you do not plan to resell your module per the NATIONAL INSTRUMENTS AGREEMENT (NI cRIO MODULE DEVELOPMENT KIT) license. You will obtain a vendor ID after purchase.
Operation mode is used to communicate with the I/O circuitry on the module. It can be used to initiate, communicate, and retrieve data. Although most modules support Operation mode, it is not a requirement. You may create a module that does not require any communication with the system and only provides an external interface through its front panel. The module interface defines 11 signal lines. Two of these signals have predefined, fixed functionality. The definition of the remaining nine signals changes depending on the selected communication mode.
The communication requirements for most modules designate that one of the two general templates be provided within the module development kit: SPI or parallel. Use the SPI template to implement a serial interface to the I/O circuitry and for EEPROM communication. Use the parallel template for simple, direct access to your I/O circuitry. The two general templates cannot meet the requirements of some modules. For example, a custom module may require two independent serial interfaces across the module interface. In this case, you can implement your own arbitrary interface with the user template. In the user template, you can use the I/O lines as general-purpose user lines.
C Series I/O modules feature stringent power and ground requirements to ensure an electrically robust system. These include traditional specifications such as power consumption from the module interface and controller power supply characteristics. Additional specifications include in-rush current for hot insertion and overall power dissipation. All C Series modules must support hot insertion, which is the ability to insert a module into a CompactRIO controller while it is powered on. To prevent the disruption of other modules in the chassis during hot insertion, the module must meet the in-rush current specification. If the in-rush current for the module is greater than the specification, the voltage supplied to the other modules in the chassis may fall below the minimum power required by the modules and cause a fault in the system. The in-rush current charge transfer must not exceed the specified limit before the current falls below the peak allowable power consumption.
||Inputs tri-stated until module is configured
||40 MHz max
|Driver slew rate
||0.2 V/ns min, 1 V/ns max pull-ups
|All signals (except sleep)
||1.5 kΩ min
||3.3 kΩ max
||10 kΩ min
||<20 mA per line, powered off
Table 2. MDK I/O Signals