Electrical computers and digital processing systems: support – Clock – pulse – or timing signal generation or analysis
Reexamination Certificate
1999-05-28
2003-04-29
Lee, Thomas (Department: 2185)
Electrical computers and digital processing systems: support
Clock, pulse, or timing signal generation or analysis
C713S001000, C713S300000, C713S320000, C713S323000, C709S200000, C709S222000
Reexamination Certificate
active
06557108
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention is related to the field of modems for use with personal computers or other similar host devices.
2. Background
When a computer, portable computer, or other host device utilizing a modem is turned on or reset, it is strongly desired that the modem quickly complete its own reset and then enter a “sleep” mode as soon as possible. A sleep mode is a condition wherein the modem, or similar device, is waiting to be utilized by the host to perform its primary tasks. While waiting in a sleep mode the device uses a minimal amount of power.
A quick to reset and sleep operation is desired for a variety of reasons. Primarily, quickly obtaining a sleep mode allows for compliance with the requirements of the standard issued by the Personal Computer Memory Card International Association (PCMCIA). Specifically, the PCMCIA standard requires that the average current during the first second after power is applied to the modem not exceed a specified value. This requirement is made to protect the host from a device which would draw too much power from it. A quick reset and sleep of the modem also provides the advantage of conserving power.
Like other components of a host, the modem's reset is initiated by the host's reset pulse. The host's reset pulse is asserted soon after power has been applied to the host or when a system reset command has been made. For a host's PCMCIA system, the reset pulse, as well as all other aspects of the system, must comply with the PCMCIA standard.
PCMCIA is an international standards body and trade association consisting of over 300 companies that has developed a standard for small, credit card-sized devices called PC Cards. Initially PC Cards were primarily used to provide additional memory to the host, but now PC Cards are used in many varied applications including several types of RAM memory, pre-programmed ROM cards, modems, sound cards, floppy disk controllers, hard drives, CD ROM and SCSI controllers, Global Positioning System (GPS) cards, data acquisition, pagers and other external devices. Complying with the PCMCIA standard provides many advantages.
Although the PCMCIA standard was originally developed for adding memory to portable computers, as noted, it has been expanded over time to cover many different types of external devices. Modems are one of these types. The PCMCIA standard requires that the average current draw during the first second after start-up of the computer not exceed a specified value. To comply with this requirement, not all of the attached devices can be running during the entire duration of the start-up. Therefore, a goal in designing a PCMCIA compatible device, such as a modem, is to have the device enter a sleep mode as soon as possible after the beginning of the start-up or reset.
Similarly, it is a goal to conserve power as prescribed by the “Berlin Power Compliance”. In meeting all the foregoing requirements the modem's Digital Signal Processor (DSP) needs to complete initialization and cause the modem to enter a sleep mode as soon as possible.
For modems, the problem which has existed to date is that if the modem simply uses the host's reset pulse to control its own reset, it will not reset and enter its sleep mode quickly enough. This is due to the fact that the modem's DSP will not begin the sleep operation until after the host reset pulse has finished. Although the DSP will start its initialization when the host's reset pulse is initially received, and the DSP may possibly even finish initialization prior to completion of the reset pulse, the DSP will only begin causing the modem to enter a sleep mode upon receipt of the trailing edge of a reset pulse. In other words, the time required for the modem to complete its reset and go to sleep has always been longer then the duration of the host's reset pulse.
For a PCMCIA system, the PCMCIA reset pulse is asserted by the host computer, via the PCMCIA controller, at the time of a start-up or a reset. The PCMCIA reset pulse, which instructs all attached components to perform their own resets, can vary in its duration. Under the PCMCIA standard, the PCMCIA reset pulse must be at least 10 micro-seconds long, but the pulse can potentially last several seconds. In circumstances where the PCMCIA reset pulse is long, the modem will fail to comply with the PCMCIA standard as the modem will take too long to reset and go to sleep.
A further problem with the PCMCIA reset pulse is that as a positive asserted pulse it is incompatible with the need of the internal components of most modems. Specifically, the DSP of most modems require that the reset pulse they receive be a negative asserted pulse. This problem has historically been resolved by simply inverting the PCMCIA pulse prior to it being received by the DSP. Typically, this inversion is performed by the modem's application specific integrated circuit (ASIC).
It is critical that a proper reset of the modem is carried out. If the reset is never issued at start-up, or if the pulse is so short that it is not recognized by the DSP, then the DSP will start running its code at some random location. Also, if the reset pulse is long enough to be recognized by the DSP, but not long enough to allow the DSP to finish initializing its critical registers, the DSP will fail to operate properly.
With modems, prior solutions to the problems presented by the limited current draw requirements of the PCMCIA standard have primarily involved two approaches. Each of these approaches have attempted to reach compliance with the standard by minimizing the time between the issuance of the host reset pulse and entry into a sleep mode. In the first approach no attempt was made to shorten the PCMCIA reset pulse. Instead, efforts were made to minimize the time needed by the modem to complete its reset and get to sleep after the completion of the PCMCIA pulse. The second approach however did seek to shorten the duration of the PCMCIA pulse by using additional external circuitry to modify the pulse.
The first approach attempted to make the modem comply with the PCMCIA specification by minimizing the time from completion of the PCMCIA pulse to when the modem was asleep. Because no attempt was made to shorten the length of the PCMCIA reset pulse, only the duration of the modem's initialization and entry into the sleep mode could be shortened. This was accomplished by minimizing the code used by the DSP to perform the initialization and entry into the sleep mode tasks. Further, time was saved by utilizing a faster storage apparatus in the modem. However, under this approach the overall time from start of the reset to entry into the sleep mode could never be shortened sufficiently to assure compliance with the PCMCIA specification. As such, this solution only worked when the PCMCIA reset pulse was relatively short.
The second approach consisted of adding circuitry to provide a greater chance of compliance with the PCMCIA standard. However, this approach was not very efficient, increased costs and used additional board space within the modem. Unlike the first approach, with the second approach the received PCMCIA reset pulse was modified so it had a shorter duration before it was applied to the DSP. The additional circuitry operated to issue a shortened reset pulse to the DSP, allowing a quicker completion of the modem's reset and entry into the sleep mode. The advantage of modifying the PCMCIA reset pulse was that since the duration of the pulse could be controlled, the reduction of time would not solely be a result of increasing the speed of the modem's reset/sleep operation. Because the reset pulse seen by the DSP would be substantially shorter than the PCMCIA pulse, the DSP would receive the release (trailing edge) of the pulse long before the PCMCIA reset pulse itself was released. This would allow the DSP to begin the entry into the sleep mode much sooner than if the DSP had to wait for the completion of the PCMCIA reset pulse.
The circuitry used in
Arnesen David
Killian Harrison
Moore David
3Com Corporation
Lee Thomas
Michaelson Peter L.
Michaelson & Wallace
Patel Nitin C.
LandOfFree
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