Introduction to Microprocessors

1
Introduction to Microprocessors

• CEC 320
• Review for Exam 1

2
Administrative

• CEC 322 lab is Thursdays 125 to 405
• KETC 130
• There is a prelab Go to the CEC 322 WEB site
• Homework Read the section on Basic 8051 Core

3
Basic Microprocessor Core
4
Block Diagram of the 8051 Core
5
8051 internal RAM Organization

• Notice there are 4 register banks, 8 registers
  each
• This was done when all programming was done in
  assembly
• Notice that there is a bit addressable space
• Register Bank Switching greatly facilitated
  Assembly language programming of interrupts
• Today, the 3 extra memory banks are used by C
  to pass parameters and assign temporary variables

6
Basic 8051 Pin Configuration

• Notice that many of the port pins have multiple
  purposes

7
Things to Remember

• The 8051 engine uses separate code memory and
  data memory
• The basic 8051 core has
• 4 eight bit I/O ports
• 2 built in timers that can be configured as
  counters
• Built in serial communications facility
• Built-in interrupt controller 5 basic
  interrupts are native
• Built-in clock oscillator circuit
• The internal data memory is very limited
• Must be shared with all registers
• Must be shared with the stack
• Internal code memory can be 2K, 4K, 8K or larger
  depending on the particular model chip
• The 8051 was designed to address 64K code memory
  and 64K data memory through the use of external
  chips
• Using external memory sacrifices most of 3 I/O
  ports
• All registers are mapped into the internal data
  memory space
• The 8051 uses an Accumulator based instruction
  set architecture
• Most modern microprocessors use a Register Based
  instruction set

8
Pop Quiz 10 minutes Closed book

• What memory architecture does the 8051 use.
• What is the other memory architecture
• What is the difference
• Name 3 peripheral functions (there are more)
  contained on the basic 8051 chip that are not
  normally found on general purpose microprocessor
  chips

9
Pop Quiz 10 minutes Closed note book

• Why do we have interrupts
• What happens when an interrupt occurs
• What happens when in interrupt completes

10
8051 Timers

• The 8051 has two built-in Timers
• Each Timer can operate in any of 3 normal modes
  and one combined mode
• 13 bit timer mode
• 16 bit timer mode
• 8 bit auto reload mode
• Split Timer Mode
• The mode control register is TMOD
• TMOD is NOT bit addressable

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TMOD
12
TCON
13
Timer Mode 2

• 8 bit auto reload
• Timer increments once per machine cycle (12 clock
  cycles)
• An interrupt is generated upon overflow
• Timer 0 vectors to interrupt location 1
• Timer 1 vectors to interrupt location 3

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Each Timer Registers

• Each Timer has two (2) eight bit registers
• labeled TL0 and TH0 for Timer 0
• labeled TL1 and TH1 for Timer 1
• The TL(X) register is incremented each machine
  cycle
• Machine cycle is clock/12
• Upon overflow, the TL(X) register is reloaded
  with the value in TH(X) and
• An Interrupt is generated
• There are no lost machine cycles

15
Important Timing Considerations

• The maximum number of machine cycles between
  interrupts is 256
• The ISR must complete its work within the 256
  cycles to avoid recursion
• Problem is much more complex if more than one
  interrupt is running at the same time
• All of the time spent in a timer ISR is
  unavailable for other work the microprocessor may
  be tasked with

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Interrupt Enable Register IE

• IE is bit addressable

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IE Bit Labels
18
Pop Quiz 10 minutes Closed note book

• Assuming
• We want to operate Timer 0 in 8 bit auto reload
  mode (mode 2)
• We want interrupts to occur every 100 mS
• Clock crystal is 22.118 MHz
• What is the timer reload value we need
• Show your calculations

19
Serial Communications 1 bit at a time

• We can send data synchronously
• Or not (Asynchronous)
• Either way we have to know where the bits are
  otherwise they all look the same

20
Common RS232 byte frames

• BAUD rate refers to the bit time rate data is
  being transferred
• 9600 BAUD means 9600 bit times per second
• Standard RS 232 Baud rates are
• 9600
• 4800
• 2400
• 1200
• 300
• 120 (very slow)

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It takes more bit times than bits to create a
serial byte frame

• Refer to the diagram Im about to draw on the
  board (this shows 10 bit times per byte of data
  the most common case)

22
Each bit time is divided into 16 clock states

• Usually a UART will have a prescale register so
  that what ever crystal you chose will produce 16
  clock states at your chosen Baud rate.
• Only certain specific crystal frequencies will
  produce exactly 16 clock states at any common
  Baud rate
• Thats why we use the 11.0592 MHz and 22.118 MHz
  crystals for the 8051

23
Matching UARTS

• The transmitting UART and the Receiving UART must
  be configured to produce the same clock state
  frequency (almost) in order to communicate
• Almost means there is an allowable error in
  frequency match

24
How the Transmitter and Receiver synchronize

• The 16 clock state generators must closely match
• The leading edge of the start bit from the
  Transmitter starts clock state counting in the
  Receiver
• From that point forward (10 bit times), the
  transmitter and Receiver must not differ by more
  than 1 or 2 clock state counts

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SCON
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Input Buffering

• The receive state machine has a receive holding
  register
• As soon as an incoming byte is received, the data
  byte is transferred to the holding register so
  that the next data byte can be clocked in
• The microprocessor has until the second byte is
  clocked in to read the first byte and clear the
  holding register

27
Output Buffering

• The Transmit State Machine has an output holding
  register
• By keeping the output holding register serviced,
  maximum byte transfer rate can be maintained

28
Hand Shake

• What if the receiving UART is full?
• Hardware handshake allows the receiving UART to
  pause or delay transmission of data bytes
• This is useful if the microprocessor is busy
• Two means of hardware handshake are available on
  the 8250
• There is no hardware handshaking on the 8051

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Things to Remember (Know)

• Draw and explain the RS 232 byte frame
• How does the Receiver synchronize with the
  transmitter
• What is handshaking
• What are the strengths and weaknesses of
• Asynchronous Communications (RS 232)
• Synchronous communications (like USB and others)