Portable computers have recently become more powerful while at the same time becoming lighter and smaller. Peripheral devices are often used in conjunction with the portable computer to provide increased functionality, such as communications ability or enhanced data storage. One example of a peripheral device is a modem, which allows a user of a portable computer to communicate with other computers using telephone lines. Reduction in the size of peripheral devices has accompanied reductions in the size of portable computers.
Some portable computer systems and peripheral devices, modems in particular, have been designed recently such that the peripheral device is contained on a thin form factor computer card which plugs into a socket recessed within the body of the computer. Such peripheral devices can be carried along with the portable computer and inserted when needed.
Historically, each of the peripheral devices (e.g. modems, memory devices, facsimile, LANs, etc.) has required its own interface circuitry for connecting to the internal circuitry of a portable computer. This interface circuitry required a separate socket for each device, and thus more space in the portable computer. For example, a modem card and a memory card each required a separate socket, and thus two sockets were necessary even though only one was in use at a given time.
Recently, devices have been devised which allow some of these various forms of computer components to be plugged into the same socket of the computer, thereby reducing space required within the portable computer. For example, an international standard which defines the physical and electrical interface specifications for the interchangeability of memory and input/output cards was introduced by the Personal Computer Memory Card International Association (PCMCIA) jointly with the Japanese Electrical Industry Association (JEIDA) in September of 1991. In addition, a specification referred to as an Exchangeable Card Architecture (ExCA) specification, dated Dec. 20, 1991, has been issued by Intel Corporation of Santa Clara, Calif. The ExCA document describes specifications which manufacturers may use to provide interfaces which are ensured of allowing the memory and input/output cards for portable personal computers of different manufacturers to be interchanged.
A socket designed to these specifications allows cards, such as modem and flash memories, to be inserted, used, and removed interchangeably in the same socket. The computer systems used typically contained at least one socket recessed within the computer, such that the inserted computer card containing the modem, flash memory, etc., is protected by the body of the computer surrounding the socket in which the components are coupled.
The PCMCIA specification provides that the personal computer cards have a 68-pin connector located at the end of the card for transmitting signals between the computer and the card. Many system manufacturers desire to connect to critical signals on the integrated circuit card which are not available through the 68-pin connector. Prior art systems are known for achieving access to signals on removably insertable integrated circuit cards other than those accessed by a standard interface.
One problem that exists in an insertable integrated circuit (IC) card system using a side-contact regime is where the side contacts are used to achieve tip-ring connections for a modem card. Two side contacts of the computer IC card socket in this case are coupled to an RJ11 port contained in the side of the computer. However, if the surface of the IC card is comprised of conducting material, then the two side contacts, and hence the tip-ring leads of the telephone fine, will be shorted together for a time during insertion of the IC card. This is an undesirable phenomenon in violation of FCC regulations because a tip-ring short specifies to the telephone central office an "off-hook" condition on the telephone line, which is clearly not the intention of the user during IC card insertion. Additionally, the card to be inserted may not even be a side-contacting card, but may be one of the many types of PCMCIA-compatible cards. If the inserted card comprises a conducting surface, and if the external telephone line is incidentally kept in place by the user, a false "off-hook" condition takes place constantly.
This problem is not limited to cases in which the socket is arranged with side contacts to accommodate modem cards. In general, even if the side contacts have other purposes (for example, local area network (LAN) card contacts), there will be problems when components on or within the computer coupled to these side contacts of the IC card socket are not electrically isolated before full insertion of the appropriate IC card.
Another problem related to removably insertable integrated circuit cards regards their cost compared to their relative ease of theft. Portable computers, by their very nature, are susceptible to theft due to the wide variety of places to which they are transported, used, and stored. Portable computers can sometimes be left unattended by the user in places less familiar to the user. Additionally, however, it is easy to imagine a situation where theft of a pocket-sized computer card is even easier to accomplish than theft of a portable computer, because a PCMCIA-standard card is almost as small as a credit card. Thus, with the proliferation of small computer cards comes a need, in many circumstances, to provide a level of security for the computer cards, making them at least as difficult to steal as the portable computer itself.