PCMCIA serial adapter cards provide one or more serial ports to a host computer. They use a PCMCIA card bus to interface with the host, and add RS232, RS422, RS485, or other types of serial ports. PCMCIA is an acronym for the Personal Computer Memory Card Association, the organization which develops and maintains standards for PCMCIA cards. Originally, these devices were known as PC cards because they were designed to add memory to portable computers. As PCMCIA standards and technologies have evolved, however, these cards were used with many types of devices. Today, specifications for PCMCIA serial adapter cards include serial protocol and adapter features, card form factor, power requirements (3.3 V and/or 5V), data transfer rate, operating temperature, and certifications.
PCMCIA serial adapter cards may have one or more independent serial interfaces, or they may have a dual interface with only physical port. Each serial interface or serial port supports one or more serial protocols. Choices include RS232, RS422, and RS485. RS232 is a serial, binary-data interface between data terminal equipment (DTE) and data communications equipment (DCE). RS422 is a balanced serial interface (greater noise immunity) for the transmission of digital data. It was designed for greater distances and higher baud rates than RS232. Like RS422, RS485 is a balanced serial interface for the transmission of digital data. The difference between RS422 and RS485, however, is that RS485 can be transformed into a multi-point application. Most PCMCIA serial adapter cards have 1, 2, or 4 channels and use DB-9 or DB-25 connectors.
Card form factor is an important specification to consider when selecting PCMCIA serial adapter cards. Type I cards are 54 mm x 85.4 mm, and can be up to 3.3 mm thick. They are commonly used are used as memory cards (RAM, ROM, Flash RAM, etc.). Type II cards are 54 mm x 85.4 mm, and can be up to 5.5 mm thick. They are commonly used in I/O devices such as data/fax modems, and in LAN adapters and non-rotating mass storage devices. Type III cards are 54 mm x 85.4 mm, and can be up to 10.5 mm thick. They are commonly used as hard drives. Type IV cards have not yet been ratified by the PCMCIA consortium; however, their size is expected to be 54 mm x 85.4 mm with a thickness of 18 mm. They will be used in large capacity hard drives. Other form factors for PCMCIA serial adapter cards include SmartMedia Card, CompactFlash, Miniature Card, Solid State Floppy Disk (SSFDC), and MultiMediaCard (MMC).