Page 77 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 5: Microcomputer System

is extremely low. The devices usually wake up from the sleep mode by external reset or by a Notes
watchdog time-out.

5.3.15 Power on Reset

Some microcontrollers (e.g. PIC) provide an on-chip power-on reset circuitry which keeps the
microcontroller in reset state until all the internal clock and the circuitry are initialized properly.

5.3.16 Low Power Operation
Low power operation is important in portable applications. Some microcontrollers (e.g. PIC) can
operate with less than 2mA with 5 V supply, and around 15 A at 3 V supply. Some other
microcontrollers may consume as much as 80 mA or more at 5 V supply.
5.3.17 Current Sink/Source Capability

This is important if the microcontroller is to be connected to an external device which draws
large current for its operation. Some microcontrollers can sink and source only a few mA of
current and driver circuits are required if they have to be connected to devices with large current
requirements. PIC microcontrollers can sink and source up to 25 mA of current from each I/O
pin which is suitable for most small applications, e.g. they can be connected to LEDs without any
driver circuits.

5.4 Example of Microcomputer
Microcomputers, personal computers (PCs), are small, lightweight, and portable. Some of them
are more powerful than some of the older, larger mainframes and minicomputers. Microcomputers
are unique in that the heart of the computer (the CPU) is contained on a single integrated chip
(IC) and the entire computer system is contained on a handful of printed circuit boards located
inside a small compact frame or cabinet. In some cases a complete microcomputer is located on a
single chip; the CPU, co-processor, and memory. Some micros/PCs are high-speed, multi-user,
multi-tasking units. Traditionally micros are used for word processing, database management,
spreadsheets, graphics, desktop publishing, and other general office applications. Currently,
micros and PCs are being used for tactical support systems, such as Naval Intelligence Processing
Systems (NIPS) and Joint Operational Tactical System (JOTS). Micros and PCs can also be used as
a SNAP system for shore-based operational commands, such as ASWOC. The operational
programs for PCs used for a tactical support system are supported externally by technical teams.
These operational programs are also updated as systems are added or replaced. Programs that
are used for word processing, graphics, and so on are abundant and can be obtained through
civilian vendors and software support teams such as Commander Naval Computer and
Telecommunications Command (COMNAVCOMTELCOM). Training for microcomputers is
obtained through formal A schools, civilian contractor schools, and OJT. Training for micros is
not NEC producing.
The following is a brief description of a typical PC/desktop system:
Small compact frame or cabinet: PCs are unique in that the frame or cabinet contains the majority
of the components for a complete system. A typical PC frame or cabinet contains the following
components:

• Backplane or motherboard for printed circuit boards
• A central processor unit (CPU) and memory printed circuit board(s) (pcb)
• Input/output pcb

• Disk controller pcb

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