68HC11 Parallel I/O Chapter 7. Microcontroller-Based System Microcontroller e.g. M68HC11 To I/O CPU:...

68HC11 Parallel I/O

Chapter 7

Microcontroller-Based System

CPUMemoryI/O

Interface

BUS

Microcontroller e.g. M68HC11

To I/O

CPU: Central Processor UnitI/O: Input/OutputMemory: Program and DataBus: Address signals, Control signals, and Data signals

Terminology

• Pin – This is a physical point that connects the microcontroller to the outside world.

• I/O – Input /Output

• Input – This is an input pin

• Output – This is an output pin

• Bidirectional I/O – This is pin which can be configured as either input or output.

• Port I/O register= This is a data register that is physically connected to a set of I/O pins

• Control register = This a control register used to configure the operation of a data port or some other function on the controller.

Terminology

• Memory-mapped I/O: Microcontroller configuration in which external I/O is accessed using normal memory access instructions. – The M68HC11 uses memory mapped I/O.

• This is in contrast to other microprocessors (e.g. Intel) which have a separate I/O address space and use special instructions to access it.

Review of Data I/O

Input Buffer

Y

Equation

inY D

Din Y

0 0

1 1

Truth Table

Symbol

Din

Input pin

Output Buffer

A

Equation

outD A

A Dout

0 0

1 1

Truth Table

Symbol

Dout

Output pin

Another meaning of “buffer”

• The word buffer is also frequently used in computer engineering to refer to a region of storage (registers or memory) that is used to hold data temporarily while it is being (or waiting to be) sent or received.– This usage is contrasted with an electrical

buffer (previous slides) which just amplifies and delays a signal.

Tri-state drivers(Three-state drivers)

Multiple Outputs

Chip A Chip B

Let A_A = 0 Let B_A = 1

0 1

What is Y?

Y

UnknownX

A AY Y

raise

lower

Tri-State Driver

Equation

0

1

Y A when OEn

Z when OEn

A OEn Y

d 1 Z

0 0 0

1 0 1

Truth TableSymbol

OEn

High Impedance State

“Open Circuit”

Active-low signal “OEn”(Output Enable)

One implementationOf a tristate buffer in CMOS…

Y

GND

Vdd

A

CMOSTransmissionGate

OEn

A

A

Output-drivinginverter

OEn

Multiple Outputs

Chip A Chip B

Let A_A=1 Let B_A=0

0 1

Y Bus

OEn OEn

controller

Floating Driver

Y=1

01

raise

Multiple Outputs

Chip A Chip B

Let A_A=0Let B_A=1

0 1

Y Bus

controller

FloatingDriver

Y=0

OEn OEn

0 1

Open Drain Output Drivers

Field Effect Transistors - FETS

Field Effect Transistor (FET)

FET acts like a “switch”If Vgate is ONE, switch is closed, connecting A and B otherwise A and B are isolated.

Vgate

A

B

Open Drain Output Driver

We can use an FET as an Output Driver

When Din=1, Dout=0

When Din=0, Dout=Z

“open circuit”

How does Dout become an ONE?

Open Drain Output Driver

When Din=1, Dout=0FET is ON, Dout=0

When Din=0, Dout=1FET is OFF, Dout is pulled up to VDD

Why do this?

Use an external pull-up resistor

VDD

R

Dout

B

Din

A

Din

Controller

Simple Data I/O Control

Data

Halt

AB

Controller sends data to Chip-A and Chip-B

However, either device can “Halt” the transfer by bringing the halt line low.

“Wired-OR” configuration

Bi-Directional I/O Buffer/Drivers

Bi-directional I/O Driver

• Allows a single pin to be configured as an input buffer or an output buffer.

Bi-Directional I/O Buffer

OEn Function

0 Output mode

1 Input mode

Function Table

Symbol

OEn Tri-state Buffer

InputBuffer

dio Pin

FromCkt

ToCkt

Note: I/O buffer is eitherInput or output

Bi-Directional I/O Bufferas Input Buffer

Symbol

OEn Floating

InputBuffer

Dio

1

To_ckt (Input)

To_ckt = Dio

Bi-Directional I/O Bufferas Output Buffer

Symbol

OEn Active

InputBuffer

Dio

0

From_ckt

To_ckt (Output)

Note: To_ckt is also From_ckt

Dio is From_ckt

68HC11 Parallel I/O Ports

Section 7.4

M68HC11 Port Summary

• PortA– 1 bidirectional, 3 input, and 4 output port– Timer port

• PortB– 8-bit fixed output port

• Used for high byte of mem. addr. in expanded mode

• PortC– 8-bit bidirectional parallel port

• Used for low byte of address & for data in expanded mode

• PortD– 6-bit bidirectional parallel or serial I/O port

• PortE– 8-bit digital or analog input port

One of the 4 outputs isbidirectional on the E9

M68HC11E block diagramFrom datasheet, p.17

Tangent on Operating Modes• The HC11 has four operating modes.

• These are selected by input signals on the MODB and MODA inputs when the chip is reset.

(from HC11 Reference Manual, p.47)

Default Memory Maps of HC11E9

(From the HC11E series datasheet, p.37)

Ports B and C are mode-dependent

Reference manual, p. 62

Example pin connections in single-chip HC11 systems

• Very simple configuration.• A small amount of external

circuitry is still needed, for:– Power supply conditioning– External clocking– Low-voltage reset– Setting mode bits

• Note there is no external ROM/RAM in this mode!– But B and C ports are available

for doing parallel I/O.

(Reference manual, p.117)

Demultiplexing address/datain Expanded modes

Datasheet, p. 34

Connecting External memoryReferenceManual,pp. 117-118

PB

PC

Connecting External Memory

ReferenceManual,p. 118

• Note in this example, the 8K EPROM Chip is Selected (CS) if A13 & A15 are high.

• And, A0-A12 are fed to the EPROM.

• Therefore, what range(s) of addresses does the EPROM chip map to?

Port A – Address $1000

• An 8-bit, parallel I/O port.

• Data address $1000 (normally)

• Multi-Function– I/O Port – Timer Port

• PACTL – Port A Control Register ($1026)– determines port function

Port A – I/O Pin Modes

• Bits 0-2: Input Bits– PA0-PA2

• Bits 3-6: Output Bits– PA3-PA6

• Bit 7 Bidirectional Bit– Direction set in PACTL

Except that PA3 isbidirectional in the E9

Port A - $1000 Data

7 6 5 4 3 2 1 0

Bits

IIO IOOOB

O=OutputI =InputB=Bidirectional

Notation:PA7 = Bit 7 of Port APA6 = Bit 6 of Port APA5 = Bit 5 of Port A……………………………….PA0 = Bit 0 of Port A

Port A Circuit SchematicO

En

PA

0

PA

1

PA

2

PA

3

PA

4

PA

5

PA

6

PA

7(o

utp

ut)

PA

7(In

pu

t)

INPUT PINS Output PINS BiDir Pin

This one is also bidirectional in the HC11E’s

Port A – I/O Port Mode

• Example:* Bit 7 configured as input (default)PortA EQU $1000* Output a $C to Port AOutdata EQU %01101000 ;Sets bits 3,5,6…………* Output data to PortA LDAA #Outdata STAA PortA* Read Data from PortA LDAA PortA

PACTL: $1026Port A Control Register

7 6 5 4 3 2 1 0

Bits

RTR0RTR1PEDGEPAMODPAENDDRA7 00

DDRA7 = Data Direction Register A70 = Input Direction (Default)1 = Output Direction

PAEN = Pulse Accumulator System Enable0 = Disable (Default) Port A is set for I/O function1 = Enable Port A is set for Pulse Accumulator function

(part of timer system, to be discussed later)

This is DDRA3 in the E series

LED Circuit Example

R

VCC

Light On

R

VCC

Light Off

Switch

68HC11 LED Example

• We’ll use PA7 for Input, PA6 for output– PA7=0 switch open, PA7=1 switch closed– PA6=0 LED off, PA6=1 LED on

• Pseudo-code:– Configure PortA ;– Repeat

• IF(PA7=0) then ; Switch is open– PA6=0 ; Turn LED OFF

• Else– PA6=1 ; Turn LED ON

• EndIF– Until Forever

Program, using BRSET/BSET/BCLR• These instructions allow us to manipulate

individual bits, but they force us to use indexed addressing to refer to the I/O registers– Extended direct mode is not available with these

particular instructions

BIT6 EQU %01000000 ; Mask for bit 6BIT7 EQU %10000000 ; Mask for bit 7

IOBASE EQU $1000 ; Base of I/O config registersPORTA EQU $00 ; Offset of PORTA ($1000)PACTL EQU $26 ; Offset of PACTL ($1026)

start: LDX #IOBASE ; Point X at I/O config registers CLR PACTL,X ; Clear all PACTL control flags.loop: BRSET PORTA,X BIT7 on ; If port A bit 7 is set, turn LED on BCLR PORTA,X BIT6 ; else, turn LED off. (Clear bit 6) BRA endif ; Go to end of if statement.on: BSET PORTA,X BIT6 ; Turn LED on (set bit 6).endif: JMP loop ; Repeat.

Simulator Example

Port B• 8-bit port

– Fixed Direction: Output

• Data address: $1004– Writing to Address $1004 will write to the port.

• Example:PortB EQU $1004Value EQU $F2

... LDAA #Value STAA PortB

• When the HC11 is in expanded mode, on boards with no Port Replacement Unit, – Port B is reserved for the upper 8 address bits (AD9-AD15)

Port B - $1004 Data

7 6 5 4 3 2 1 0

Bits

OOO OOOOO

O=Output

Port C

• 8-bit bidirectional port• Data address: $1003• Multi-Function:

– In single-chip mode, or with a Port Replacement Unit• I/O Port • Latched data from Port C is available at address $1005

– It’s latched when a rising edge occurs on STRA pin• Handshaking port

– In expanded mode with no Port Replacement Unit, • Used for low 8 bits (AD0-AD7) of memory address bus and

for memory data bus (D0-D7)

• PIOC – Parallel I/O Control Register C determines function

Port C - $1003 Data

7 6 5 4 3 2 1 0

Bits

BBB BBBBB


DDRC - $1007

7 6 5 4 3 2 1 0

Bits

DDC0

DDCn: 0 = Input (Default) 1 = Output

DDC1DDC2DDC3DDC4DDC5DDC6DDC7

DDCn= Data Direction Bit n

PORTCL - $1005 Latched Data

7 6 5 4 3 2 1 0

Bits

BBB BBBBB


PIOC - $1002 (STAF Bit)Parallel I/O Control Register

7 6 5 4 3 2 1 0

Bits

INVBEGAHNDSCWOMSTAISTAF OIN PLS

STAF = Strobe A Flag 0 = Inactive (default) 1 = Set at the active edge of STRA pin

Read only bit. Used to determine when data have been latched into Port C. Cleared after bit has been set and read.

PIOC - $1002 (STAI Bit)Parallel I/O Control Register

7 6 5 4 3 2 1 0

Bits


STAI = Strobe A Interrupt Enable 0 = No hardware interrupt generated (default) 1 = Interrupt requested when STAF=1

Enables or disables the interrupt request from being generated when STRA is asserted.

PIOC - $1002 Parallel I/O Control Register

(CWOM and EGA Bit)

7 6 5 4 3 2 1 0

Bits


CWOM = Port C Wire-OR Mode 0 = Normal Outputs (default) 1 = Open Drain Outputs

EGA = Active Edge Select for STRA 0 = Falling edge (High to Low) 1 = Rising edge (Low to High)

Port D

• 6-bit

• Address $1008

• Multi-Function– Bidirectional Port – Serial I/O Port

• Serial Communications Interface (SCI) – Asynchronous (i.e. no clock signal needed)

• Serial Peripheral Interface (SPI)– Synchronous (i.e. a clock signal needed)

Port D - $1008 Data Register

7 6 5 4 3 2 1 0

Bits

BBB BBBXX

X=Not UsedB=Bidirectional

DDRD - $1009

7 6 5 4 3 2 1 0

Bits

DDD0

DDDn: 0 = Input (Default) 1 = Output

DDD1DDD2DDD3DDD4DDD5XX

DDDn= Data Direction Bit n

SPCR - $1028 SPI Control Register

7 6 5 4 3 2 1 0

Bits

SPR0SPR1MSTRDWOMSPESPIE CPOL CPOH

SPIE = SPI System Enable 0 = Disable (default) 1 = Enable This bit should be 0 to use Port D for parallel I/O

DWOM = Port D Wire-OR Mode 0 = Normal Outputs (default) 1 = Open Drain Outputs

SCCR2 - $102DSCI Control Register 2

7 6 5 4 3 2 1 0

Bits

SBKRWUILIERIETCIETIE TE RE

TE = Transmit Enable 0 = Disable (default) 1 = Enable This bit should be 0 to used Port D for parallel I/O

RE = Receiver Enable 0 = Disable (default) 1 = Enable This bit should be 0 to used Port D for parallel I/O

Port E

• 8-bit

• Address $100A

• Multi-Function– Digital Input Port – Analog Input Port (Built-in A/D)

Port E - $100A Data Register

7 6 5 4 3 2 1 0

Bits

III IIIII


Handshaking I/O

Section 7.5

Problem

• Need to transfer data to and from Source to 6811

DataSource

6811

Several Approaches

• Simple Strobed I/O

• Full Handshaking I/O

• Let’s look at several examples

Simple Strobed I/O

• Data Bus• Single Control line

between Source and 6811

Data Bus

ControlBus

DataSource/RCVR

6811

Simple Strobed Input

Data source places data on bus, uses strobe to indicate “the data is now valid”

6811Data

Source

Data_out Data_inN

Strobe STRA

Simple Strobed Input

• Timing Diagram

DATA

Strobe

This edge indicates that the “data are now valid”

Use this edge to “latch” the data into the 6811

Simple Strobed Output

6811 uses strobe to indicate to the receiver thatData are available

DataRcvr

6811

Data_in Data_outN

Ready STRB

Simple Strobed Output

• Timing Diagram

This edge indicates that the data are “ready”

DATA

STRB

Simple Strobed I/O

• Advantage - – Simple

• Disadvantage– Must know timing relationship between data

source/rcvr and 6811. • Input: How fast can 6811 accept new data.• Output: How fast can receiver accept data

from 6811

Simple Strobed I/O: Using the 6811

Page 131


• PORTC is used for strobed input– Read data from PORTCL ($1005)– External pin: STRA is used to latch data

• PORTB is used for strobed output– External pin: STRB is used as output ready


• SET HNDS bit (bit 4) in PIOC control register ($1002) to 0

• SET EGA bit (bit 1) in PIOC control register ($1002) to desired active edge– 0 = High to Low (falling)– 1 = Low to High (rising)

• SET INVB to set active edge of output strobe– 0 = active low (High to low)– 1 = active high (low to high) (default)

Simple Stobed Input

PORTC PORTCLLATCH

$1003 $1005

STRA PIN

InputPins

Reading Input

• STAF bit in PIOC is set when new data are written into latch.

• Reading STAF bit will reset it to zero

• Let’s look at an example

Reading Input

• Configure PortC for input– Write $00 to DDRC ($1007)

• Configure PortC via PIOC ($1002) for– No interrupts (STAI=0)– Active High Inputs (EGA=1)– Active High Outputs (INVB=1)– Simple Handshaking (HNDS=0)– Config bits = %00000011

Reading Input

• Repeat• Read STAF• Until STAF=1• Read PORTCL ($1005) ; This clears STAF

Simple Stobed Output

PORTB

STRB

$1004

Writing Output

• Writing to Port B will automatically assert the STRB pin for two clock periods.

• Use INVB to control the polarity on STRB– 0 = Active low– 1 = Active high

Full Handshaking I/O

Page 130

Full Handshaking I/O Protocol

• Data Bus• Two Control Lines

Data Bus

ControlBus

ExtDevice

6811

Full Handshaking I/O

• Disadvantages– More complicated I/O

• Advantages– Control timing relationship between 6811

and External Device

Input Handshaking

• Input Handshaking

1. Ext. Device places data on bus2. Device asserts “strobe” to indicate “data is available.”3. Ext. Device asserts “strobe” to indicate “acknowledgement” or “I have the data.”

ExtDevice

6811

Data_out PortCN

Ack STRB

Strobe STRA

Input Handshaking

This edge indicates to the 6811 that “data are available.”

This edge indicates to the External Device that “I have the data.”Ext. Device can send the next byte

Data

STRA

STRF

STRB

InternalFlag

Reading Input Full Handshaking

• Configure PortC for input– Write $00 to DDRC ($1007)

• Configure PortC via PIOC ($1002) for– No interrupts (STAI=0)– Active High Inputs (EGA=1)– Active High Outputs (INVB=1)– Full Handshaking (HNDS=1)– Input Handshaking (OIN=0)– STRB Level mode select (PLS=0)– Config bits = %00010011

• Read input as in Simple Input example

Output Handshaking

1. 6811 asserts STRB that says “data are available.”2. Ext. Device reads data.3. Ext. Device asserts “strobe” to indicate that I have the “data.” Ready for another byte.

ExtDevice

6811

Data_out PortC

N

Ready STRB

Strobe STRA

Output Handshaking

This edge indicates to the External Device that “data are available.”

This edge indicates to the 6811 that “I have the data.” 6811 canSend another data byte

Data

STRA

STRF

STRB

Writing Full Handshaking

• Configure PortC for output– Write $FF to DDRC ($1007)

• Configure PortC via PIOC ($1002) for– No interrupts (STAI=0)– Active High Inputs (EGA=1)– Active High Outputs (INVB=1)– Full Handshaking (HNDS=1)– Output Handshaking (OIN=1)– STRB Level mode select (PLS=0)– Config bits = %00011011

• Read input as in Simple Input example

68HC11 Parallel I/O Chapter 7. Microcontroller-Based System Microcontroller e.g. M68HC11 To I/O CPU:...

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