GB2166024A - A modulator/demodulator and a portable digital computer incorporating the same - Google Patents

Abstract

A modem has a LINE terminal (310) which is connected to telephone line terminals TIP (402) and RING (403) by way of an isolating transformer (401). The LINE terminal is connected to the receive and transmit lines within the modem. These lines are preferably also connected to terminals for an acoustic coupler. The modem is very lightweight so that it may be incorporated in a portable computer. In particular the transformer (401) is very small. This renders it liable to damage from power surges on the telephone line but the transformer is protected by varactors (404,405) connected across the telephone line. <IMAGE>

Description

SPECIFICATION A modulator/demodulator and a portable digital computer incorporating the same This invention relates to a modulator/demodulator (modem) and also to digital computers, and particularly to extremely small, lightweight digital computers with extremely low power consumption.

A recent trend in digital computers is the "personal computer". A strong thrust within this trend has been the portable computer, recently culminating in the extremely small and lightweight "lap" computer. Numerous technical problems need to be overcome in order to produce a computer small enough to fit in a briefcase, weighing under 4.5 kg and able to operate six hours or more on internal batteries.

Other problems need to be overcome in order to provide such computers with a full range of features. Since it is recognized that such computers are constrained to having limited internal storage, it is desirable to equip them with communications capability so that they can communicate via telephone lines with larger computers and transfer blocks of data to and from them, thus augmenting the limited internal storage. Ideally, such communication capability should be able to access the phone lines either directly via a wired connection, or through an acoustic coupler.

One object of the present invention is to provide a lightweight, small modem for use in a portable computer.

It is a further object of the present invention to facilitate construction of small, lightweight, low-power portable digital computers with the ability to communicate directly over telephone lines.

The modem according to the invention is defined in claim 1 below.

The present invention overcomes the aforementioned problems of the prior art and enables a computer with a full range of features, including telephone communications capability to occupy a package small enough to fit in a brief case, to weigh less than 4.5 kg and to operate for more than six hours on included batteries.

Thus, an extremely small telephone isolation transformer is used, along with the use of protective elements to prevent damage from surges that might ordinarily destroy so small a transformer. Preferably the modem includes an interface circuit that facilitates phone line access either via a direct wire connection or an acoustic coupler.

The invention will be described in more detail, by way of example, and with reference to the accompanying drawings, in which: Figures 1Fa)-1(c) are views of a portable computer using a modem and modem control circuitry including the present invention.

Figure 2 is a block diagram of a portable computer using a modem and modem control circuitry including the present invention.

Figures 3(a) and 3(b) comprise a logic/schematic diagram of the modem of the present invention.

Figure 4 is a schematic diagram of a data access arrangement (DAA).

Figs. 1(a) to 1 (c) depict the external appearance of a portable computer which includes a modem and a data access arrangement. Fig. 2 is a block diagram of the elements of the portable computer, which is seen to comprise a main printed circuit board 201, including a CPU 214 and a memory 215, an I/O printed circuit board 206, and a modem 211, interconnected by data bus 203. The main PCB 201 can accept input from a keyboard 205 and present outputs to a liquid crystal display 204 which can display at least 400 characters, preferably 25 rows of 80 characters each (2000 characters). The I/O PCB 206 has serial interfaces 207 and 208 through which serial devices, such as line printers, may be connected to the computer; it also interfaces two disk drives 209 and 210 to the computer.The modem 211 can interface the computer to the telephone system, either by connecting a telephone line directly to a data access arrangement 212, or through an acoustic coupler 213 in conjunction with an ordinary telephone set. The main PCB 201 can issue control signals 214 to the I/O PCB 206 and the modem 211.

The computer can be powered by an internal power supply operating off the mains or by batteries which fit within the casing of the computer. This has dimensions which are no more than 30.5 cm by 25.4 cm by 7.6 cm.

The total weight with the batteries included is less than 4.5 kg. The batteries allow at least six hours use.

Figs. 3(a) and 3(b) comprise a logic and schematic diagram of the modem 211. Microprogramming Unit (MPU) 301, which may be an 80C49 integrated circuit, exercises overall control over the modem. Tone generator 303, comprising two 14556B IC's and a 5089 IC, generates the audio tone TONE 318 onto which data are to be modulated. Universal Synchronous/Asynchronous Receiver/ Transmitter (USART) 304, which may be an 82C5 1 IC, translates serial data sent or received into parallel bytes of data on data bus 203, as will be discussed further below. Modem chip 305, a TM599532A IC, modulates bits serially onto the audio tone for transmitting, and demodulates bits serially from the audio tone when receiving.

Amplifier 306 drives the modem output into the data access arrangement, while amplifier 309 drives it into the speaker of the (external) acoustic coupler. Amplifier 307 drives the signal received from the data access arrangement into the modem, while amplifier 308 drives the signal received from the microphone of the external acoustic coupler into the modem.

Amplifiers 307 and 308 may each contribute to the signal RCVA 311, which is the modem signal input. Amplifiers 306 and 309 are both driven by the modem output TXA. The signal line named LINE 310, which connects to the telephone line through the data access arrangement, drives amplifier 307 on receive, or is driven by amplifier 306 on transmit.

Among the control signals 214 passing between the modem and the main PCB 201 are MODEM SEL 312, MODEM ENB 313, and RE SET 314.

Fig. 4 is a schematic diagram of the data access arrangement 212. It is seen to provide the interface between the internal signal named LINE 310 and the telephone line (TIP 402 and RING 403). Isolation and coupling are provided by a transformer 401, which, in keeping with the power, size, and weight constraints of the portable computer in which this invention is to be used, is a much smaller and lighter transformer than is customarily used in such applications. In order to protect this transformer from surges that may appear on the telephone line, varactors 404 and 405 are connected across the telephone line. Ring detector 406 (which may be a TCM1520A IC) is also connected across the telephone line and in response to a ring signal appearing thereon will generate the signal RI 407.

Detailed operation: 1. Receiving through the data access arrangement: A signal comprising digital data FSK modulated onto an audio tone appears across TIP 402 and RING 403, whence it is coupled by transformer 401 onto LINE 310. The signal is amplified by amplifier 307 and appears as RCVA 311. RCVA 311 is input to modem 305, which demodulates the data: i.e. the data bits as represented by frequency shifts on an audio tone are translated to logic level bits appearing serially on RXDA 316. The bits appearing serially on RXDA 316 are input to USART 304, which assembles eight-bit bytes and forwards them in parallel to the main PCB via data bus 203.

2. Tranmitting through the data access arrangement: Eight-bit bytes to be transmitted are forwarded from the main PCB 201 over data bus 203, whence they are input to USART 304.

USART 304 present the bits serially on TXD A 315, which inputs them to modem 305.

Also input to modem 305 is TONE 318 from tone generator 303. Modem 305 produces an FSK representation of the bits on TX 317, which is amplified by amplifier 306 and presented on LINE 310. From Line 310 the signal is coupled by transformer 401 onto the telephone line (TIP 402 and RING 403).

3. Receiving through an acoustic coupler: An FSK-modulated signal incoming on a telephone line to an external telephone set properly positioned in an external acoustic coupler will energize the microphone of the acoustic coupler, and the signal will thus appear on the MIC IN input to amplifier 308, which presents the signal on RCVA 311. Operation is thereafter is described under item 1 above.

4. Transmitting through an acoustic coupler: Operation is as described under item 2 above as far as producing an FSK-modulated signal on TXA 317. The signal is amplified by amplifier 309 and presented on the SPK OUT output therefrom, whence it energizes the speaker of an external acoustic coupler. Assuming an external telephone set to be properly positioned therein, the coupler's speaker will energize the telephone's microphone, whereby the signal will appear on the telephone line.

Claims (4)

1. A modem for communicating digital data between telephone lines and a digital device, comprising a transformer with two windings, one connected to components of the modem, the other being provided for connection across a telephone line, the transformer serving to isolate the telephone lines from the remainder of the modem and from the digital device, and to couple signals between the telephone lines and the remainder of the modem, the transformer being so small as to be liable to be damaged by power surges on a telephone line but being protected by means connected across the said one winding and capable of discharging power surges on a telephone line.

2. A modem according to claim 1, wherein the protective means comprises one or more varactors connected across the said one winding of the transformer.

3. A modem according to claim 1, wherein an input/output circuit is connected both to the said other winding of the transformer and to an acoustic coupler circuit to provide the option of communication by wired connection or through an acoustic coupler.

4. A portable lap-held digital computer incorporating a modem according to claim 1, 2 or 3, a CPU for performing operations on data, a memory for storing data and instructions, a display device connected to the CPU and the memory for displaying at least fourhundred characters of information specified by the CPU means, a typewriter-like keyboard for keying data and instructions into the memory, disk drive means for storing data and instructins, I/O means for interfacing the disk drive means and one or more external I/O devices to the CPU and the memory, bus means for interconnecting the CPU, the memory, the I/O means, and the mode, and a power supply unit for powering the digital computer and the modem, the power supply means optionally including batteries, the digital computer and modem being capable of continuously operating for at least six hours powered only by the batteries without replacing or recharging the batteries, the computer, including batteries, having overall dimensions of less than 30.5 by 25.4 by 7.6 cm and the package, including batteries, having a weight of less than 4.5 kg.