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Midsize Microcontrollers and Microprocessors

The 8051 is an example of a small inexpensive microcontroller intended for simple applications.

Other examples are the PIC and the Atmel AVR. There are also a large number of more powerful

“midsize” microcontrollers available. These include embedded X86 processors.

These typically provide more memory, more I/O and faster performance.

We will consider an interesting example, the Rabbit 3000 developed by Z-world.

The Rabbit processors are enhancements of the Z80 processor.

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The 3200 Core module Rabbit Semiconductor sells the 3000

as a module. For modest volume applications

using this module is more viable than building a system form scratch.

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Rabbit 3000 Processor 8-bit data bus 20-bit address bus

Internal peripherals use 8 bit address bus

Static design - DC to 54 MHz Clock Programmable chip select outputs Clock Spreader results in Ultra-Low EMI Communication Features

Hardware and/or software support for TCP/IP, IrDA, SDLC/HDLC, Async, SPI, I2C

56+ Digital I/O 6 Serial Ports 1.8-3.6 V (5 V tolerant I/O) Watchdog Timer Extended Low-Power "Sleepy" Modes

Dynamic, software-enabled low-power modes

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Processor Registers

Multiple Accumulators A – 8 Bit HL – 16 Bit

Memory Mapping IX,IY – Index Registers XPC – Extension of PC

Two Register Banks A, F, HL, DE, BC all have

alternate registers. EX AF, AF’ swaps AF and

A’F’ EXX swaps HL, DE, and BC

with H’L’, D’E’, and B’C’.

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Parallel I/O ports Seven 8-bit I/O ports. (A-F)

I/O pins are shared with other on-chip peripherals.

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Other ports Six Serial Ports

Maximum baud rate of system clock divided by 8

Several enhancements over standard asynchronous communications.

The serial ports can be used for processor to processor communication.

A parallel slave ports are also provided for processor to processor communication.

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Slave port example

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Quadrature Decoder

Two channels for encoder input (IQ)

8-bit counter is incremented or decremented to keep track of encoder’s position.

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Pulse width modulation (PWM) channels. PWM is useful in many applications from audio

generation to motor control. Four independent channels are provided. The Rabbit PWM module is straightforward—a

single 10-bit free-running counter counts from 0x000 to 0x3FF (0 to 1023) and rolls over. The application program loads a PWM “width” register with a value “n.” Out of 1024 counts, the PWM’s output pulse is high for n+1 counts. This gives the application the ability to vary the duty cycle from about 0.1% to 100%. 1024 ticks from timer A9 define the overall period.

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Timers – two timer modules A and B

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Memory - MMU and MIU MMU – memory management unit MIU – memory interface unit Combination allow for addressing 6 MB 20-bit physical address for 1 MB Internally 16 bit address are used (64

KB) MMU uses special segment registers to

map 16 bit address to 20 bit address.

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Base (or Root) Segment 0000 00000 Data Segment X000 DATASEG|000 + X000 Stack Segment Y000 STACKSEG|000 + Y000 Extended Memory Segment E000 XPC|000 + E000

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Memory Mapping Example

Example The MMU registers are set as follows: XPC        = 0x85 SEGSIZE    = 0xD7 STACKSEG   = 0x80 DATASEG    = 0x79

The physical address of the bottom of the xmem segment is given by:

0x85000 + 0x0E000 = 0x93000

The physical address of the bottom of the stack segment is given by:

0x80000 + 0x0D00 = 0x8D000

The physical address of the bottom of the data segment is given by:

0x79000 + 0x07000 = 0x80000

Base (or Root) Segment 0000 00000Data Segment X000 DATASEG|000 + X000Stack Segment Y000 STACKSEG|000 + Y000Extended Memory Segment E000 XPC|000 + E000

Y X

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MIU