Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2003-01-08
2003-12-23
Cumming, William (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
Reexamination Certificate
active
06668180
ABSTRACT:
The invention relates generally to signaling between a host and a human-input device such as a keyboard, and relates more particularly to such signaling in systems where it is desired to minimize power consumption and maximize battery life.
BACKGROUND
The earliest personal computers were powered by AC (mains) power and thus there was little need to worry about power consumption. Such computers were also stationary rather than portable and thus there was little need to worry about weight or size. Such a computer typically has a keyboard that is roughly the size of a traditional typewriter keyboard. The keys are typically laid out with the keys “Q,” “W,” “E,” “R,” “T,” and “Y” in a row, and the keyboard is sometimes called a “QWERTY” keyboard.
In more recent times, however, consumers have shown greater interest in computers that are small and light in weight. A typical “personal digital assistant” or PDA is small enough to fit into a shirt pocket and weighs less than a pound. The PDA form factor is possible only because the designer forgoes a conventional keyboard and pointing device. The default mode of human input with such a host is a stylus applied to a touch-sensitive display screen.
A natural next step is to attempt to interface a QWERTY keyboard with a PDA. As it turns out, there are several reasons why this is not easy. First, the PDA will probably not have been designed from the outset to connect with a keyboard at all. Second, the I/O port or ports provided by the PDA designer will probably be poorly documented or not documented at all, and will not be well suited to use by a third-party designer of human input devices. Third, the operating system of the PDA will probably be poorly documented, and latency in responding to interrupts and other asynchronous inputs is likely to be variable and not easy to predict.
Finally, the PDA will have been designed to minimize power consumption and thus to maximize battery life, and the design decisions that minimize power consumption tend to disfavor other potential design goals. For example, the PDA will have at least two power consumption levels, a higher level which displays information and responds to user inputs, and a low-power or “sleep” level which preserves memory contents and otherwise consumes only the power required to respond to any of certain defined “wake-up” inputs.
One popular PDA is the Palm Pilot, which has a “hot sync” port used with a cradle for synchronization of a database between the PDA and a personal computer. The cradle connects to the personal computer by means of a serial data port. The interface between the PDA and the cradle is a serial interface with other pins for power and ground and handshaking. The cradle has a “sync” button which (among other things) communicates a “wake-up” signal to the PDA if it is not already awake, and readies the PDA for the “hot sync” procedure.
Given that the only workable I/O port may be the “hot sync” port, the designer of an external keyboard may well find that there is no choice but to attempt to interface with that port. The designer will, ideally, be able to design a “driver” which is loaded into the RAM of the PDA, which driver is to receive signals from the keyboard and to provide them to the operating system. In this way, a keystroke at the keyboard will be communicated to the operating system in a way which brings about the same results as a keystroke communicated to the operating system by other means. The designer must, however, necessarily attempt to take account of the possibility that the PDA maybe be in “sleep” mode at the time that a key is pressed by a user. The keyboard would then need to buffer the key-press information, awaken the PDA, and pass the key-press information to the driver (and thence to the operating system).
Experience shows, however, that there is much to go wrong in such a system.
A signaling method directed to these ends is described in International Patent Application no. PCT/US00/08521, published Oct. 12, 2000 as WO 00/60438, page 32, line 30 to page 39, line 25, and FIG. 33.
In a prior-art system, the keyboard encoder of the keyboard has a serial interface and is designed for use with a Palm Pilot PDA running the Palm Operating System (Palm OS), with emphasis on low power consumption. The encoder is connected to the Host PDA via five wires. Two lines (V+ and Ground) provide operating power, and three lines provide the interface. One interface line is “Request-to-Send” (RTS) which provides a hardware handshake. If RTS is asserted, this means the serial interface is active. If RTS is not asserted then the serial interface is not active, for example, during a “sleep” condition of the PDA. Another interface line is the HotSync line, which is an Interrupt pin with wake-up capability connected directly to the main CPU in the Host.
It is helpful to define an “Idle time” for the serial interface of the host, defined as the time when the RS232 Interface is activated, but no data transmissions occur. Experience shows that the RS232 Interface in the Host consumes power during both Idle time and the actual receive operations. In order to reduce the power consumption, it is paramount to reduce the Idle time. Depending on the operations of the Driver in the Host, the Idle time might be reduced to 3 seconds or less (and perhaps as little as 300 ms). The fortunate result (from the power-conservation point of view) is that the Encoder (and external keyboard) may turn out almost to have no impact on the total average power consumption of the whole system, and the service life of a single set of batteries is essentially the same with or without the Encoder attached to the Host.
Importantly, permitting both the Encoder IC and the Host to shift into “stopped” or very-low-power operations make it possible to achieve a small average operating power.
With the prior-art system, when the key is actually pressed, the Encoder IC is awakened first, and after a brief processing and verification delay, the Host is aroused too by activation of the HotSync line. While the designers of the Palm specifically designed the HotSync pin for this purpose, it can serve the more general function of indicating manually to the PDA that some new external device or cabling has just been attached. For example, if the user presses a button, this usually evokes the HotSync signal. The exemplary prior-art chip simulates the button press with the digital output pin, activating the HotSync line quite often. As will be appreciated, in practical terms it may develop that the HotSync line is activated for nearly every keystroke.
With the prior-art system, the basic operations can be described as:
1. Sensing a key press on the key matrix
18
;
2. Looking at the RTS line to determine if the RS232 Interface is active;
a. If RTS is not active, then pulsing the HotSync line
14
;
b. waiting for RTS line to become active;
c. And possibly repeating the HotSync if the previous one wasn't acknowledged by the actions of the RTS line (e.g. it was lost, for some unknown reason, in the OS);
3. Sending the Report of the Key Press to the Host
11
;
4. Waiting for the key to be released while reporting any new keys using method of #
1
through #
3
;
5. When key is released—sending the release information to the Host
11
;
6. When all keys are released (that is, when the keyboard is idle), the IC
10
reduces its power consumption to almost zero;
7. When all of the keys are released (the keyboard is idle), the Driver may de-activate the RS232 port (and RTS line).
Using the above steps in the operations of the complete Host-Encoder system, a dramatic reduction of power consumption is achieved.
There are, however, difficulties with this approach. For example, experience shows that the response of the Host to the HotSync and the handling of the Serial Port is not instantaneous and deterministic. The Palm OS is a multitasking OS, and execution delays can depend on exactly what the Host is doing at the present time. Particularly troublesome is the fact that the Host's response to the
Marten Victor
Shafranov Andrew
Vanstone Mark
Cumming William
Oppedahl & Larson LLP
Semtech Corporation
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