M-Modules are ANSI/VITA 12-1996 mezzanine cards that are used mainly in industrial computers. They communicate with a printed circuit board (PCB) carrier over a dedicated bus and feature a fast, asynchronous parallel interface. As mezzanine cards, M-Modules remain connected to a PCB carrier. Unlike some other I/O boards, however, M-Modules also conform to ANSI/VITA 12-1996, a standard from the American National Standards Institute (ANSI) and the VMEbus International Trade Association (VITA) that defines minimum electrical and mechanical characteristics along with thermal specifications. Although both single Eurocards and double Eurocards remain popular, M-modules are low-cost devices that provide flexibility to users who need to implement custom solutions, especially when configuring a test, data acquisition, or control system.
M-Modules differ in terms of functionality. Choices include analog I/O modules, bus interfaces and adapter modules, data acquisition devices, digital multimeters, digital I/O modules, function generators, mass storage modules, and memory modules. Mezzanine cards that provide motor control, network interfaces, and serial communications are also available. When selecting M-Modules, note that some interfaces and adapters are designed to translate the data from the M-Bus to another bus, and vice versa. Products that are described as networking modules are actually network adapters for protocols such as Ethernet and Token Ring. Serial communication M-modules interface the host with a PMC bus and add RS232, RS422, or other types of serial ports. PMC (PCI Mezzanine Card) is a low profile mezzanine card for computer systems with logical and electrical layers based on the Peripheral Component Interconnect (PCI) specifications.
M-Modules carry products specifications for number of channels, throughput rate, clock rate, bus width, and voltage supplied to modules. The number of channels is the total amount for the M-Module. Throughput rate is the transmission speed in Hertz (Hz). The clock rate is the rate at which the module slot operates. Choices include 8 MHz, 32 MHz, and 64 MHz. The bus width is the number of bits that M-Modules can transmit at a time in parallel. Choices include 8 bits, 16 bits, and 32 bits. There are three main choices for the voltage supplied to M-Modules: -12 V, 5 V, and 12 V.