Portable information terminal

• US 6,728,812 B1
• Filed: 12/14/1999
• Issued: 04/27/2004
• Est. Priority Date: 06/16/1997
• Status: Expired due to Fees

• Current Assignee: Citizen Holdings Co., Ltd.
• Original Assignee: Citizen Watch Co Limited (Citizen Electronics Company Limited)
• Inventors: Kato, Yuichi
• Primary Examiner(s): Myers, Paul R.
• Application Number:
  US09/445,829
• Time in Patent Office: 1,596 Days
• Field of Search: 711/152, 711/163, 711/103, 710/316, 710/301-304
• US Class Current: 710/303
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 1/1632 External expansion units, e.g. docking stations

Abstract

A portable information terminal has at least a programming ROM, a work RAM, a data storage memory, an input key, a liquid crystal display panel, a liquid crystal driving control circuit, a built-in battery, and a central processing unit which is operated by using the programming ROM and the work RAM and displays data in the data storage memory on the liquid crystal display panel. Further, the portable information terminal comprises a switching control circuit which outputs a switching signal in accordance with an input signal from an external computer apparatus connected to the terminal, a control signal switching circuit which switches an address bus, a data bus and memory control signal lines which are connected to the central processing unit to an address bus, a data bus and memory control signal lines which are connected to the external computer apparatus in accordance with the switching signal in order to access the data storage memory from the external computer apparatus, and a serial signal switching circuit which switches a PCMCIA bus control signal to a serial signal in accordance with an input signal from a serial interface device which is connected between the portable information terminal and the external computer apparatus. Still further, the portable information terminal comprises a recognition circuit which recognizes the serial interface device and a PCMCIA standard female connector which is connected to the serial connector which is connected to the serial interface device.

Claims

1. A portable information terminal electrically connectable to external computer apparatus via a connector such that said external computer apparatus can access said portable information terminal, comprising:

an internal memory for receiving information stored in a memory in said external computer apparatus and storing the same in said internal memory following access by said external computer apparatus;

a central processing unit capable of accessing said internal memory;

display means for displaying said information stored in said internal memory;

first control means for enabling said external computer apparatus to access said internal memory; and

said internal memory and said central processing unit being separately connected to said first control means;

wherein access from said central processing unit to said internal memory is prevented and access from said external computer apparatus to said internal memory is enabled when said external computer apparatus and said portable information terminal are connected.

2. A portable information terminal as claimed in claim 1, further comprising:

a power source; and

a power source switching circuit for switching said power source of said portable information terminal to a power source of said external computer apparatus when said external computer apparatus and said portable information terminal are connected.

3. A portable information terminal as claimed in claim 1, further comprising a PCMCIA standard female connector for connecting the portable information terminal to said external computer apparatus.

4. A portable information terminal as claimed in claim 1, wherein said internal memory comprises an SRAM or a flash memory.

5. A portable information terminal as claimed in claim 1, wherein said display means comprises a monochrome reflection liquid crystal display panel or a color reflection liquid crystal display panel.

6. A portable information terminal as claimed in claim 1, wherein said first control means comprises a switching circuit which prevents said central processing unit from accessing said internal memory by outputting a switching signal following an input signal from said external computer apparatus.

7. A portable information terminal as claimed in claim 1, wherein said first control means prevents said central processing unit from accessing said internal memory when a power source signal input is received from said external computer apparatus.

8. A portable information terminal as claimed in claim 6, wherein said switching circuit outputs said switching signal based on a power source signal as the input signal from said external computer apparatus.

9. A portable information terminal as claimed in claim 2, wherein said first control means is included in an ASIC which is formed as a one-chip semiconductor.