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I/O and Interrupts. Today: First Hour : I/O Concepts Section 6.1-6.6 of Huang’s Textbook In-class Activity #1 Second Hour : Interrupt Code Example In-class Activity #2. Goal: Example Task. - PowerPoint PPT Presentation
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I/O and InterruptsI/O and Interrupts
Today:• First Hour: I/O Concepts
–Section 6.1-6.6 of Huang’s Textbook
– In-class Activity #1
• Second Hour: Interrupt Code Example
– In-class Activity #2
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Goal: Example TaskGoal: Example TaskRead the output of the 4-bit data source every time the push
button is pressed, and display the result.Read the output of the 4-bit data source every time the push
button is pressed, and display the result.
4-bit Data
Source
Push Button
Computer(HC11 chip)
Display
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ROM-8KB
RAM-256 bytes
EEPROM-512 bytes
PORTA
PULSE ACCUMULATOR
PERIODIC INTERRUPT
COP WATCHDOG
PAIOC2
OC3OC4OC5
OC1
IC1
IC2IC3
PA7
PA6PA5PA4PA3PA2PA1
PA0
PE7
PE6PE5PE4
PE3
PE2
PE1PE0
PORTE
VREFH
VREFL
A/DCONVERTER
DA
TA
DIR
EC
TIO
N
PORTD
SSSCK
MOSI
MISO
SPI
TxD
RxDSCI
PD5
PD4PD3
PD2
PD1
PD0
M68HC11 CPU
ADDRESS DATA BUS
INTERRUPTS
RESET
XIRQ
IRQ(V
PPBULK) HANDSHAKE I/O
DATA DIRECTION C
PORT CPORT B
PARALLELI/O
SINGLECHIP
PB7
PB6
PB5
PB4
PB3
PB2
PB1
PB0
PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
STRA
STRB
A15
A14
A13
A12
A11
A10
A9
A8
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
R/W ASEXPAND
OSCILLATOR
XTAL
EXTAL
E
MODALIR
MODB(VSTBY )
VDD
VSS
MODESELECT
POWER
M6811 PortsM6811 Ports
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PortsPorts• Way to read/write from/to peripheral devices• Some ports allow both input and output (see your PRG!)• Each port has:
–Control Registers–Status Registers–Data Registers–Data Direction Registers
• The ports are memory mapped, which means that you can access these registers via memory!– I/O becomes a simple matter of reading/writing to
these special memory locations!
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Look up PRG! - The 68HC11A8 has 40 I/O pins that are arranged in five I/O ports.- All I/O pins serve multiple functions.- Ports C and D are bi-directional I/O pins under the control of their associated data direction registers. - Port C, port B, the STRA pin, and the STRB pin are used for strobed and handshake parallel I/O, as well as for general-purpose I/O.
Port Registers- To input, the 68HC11 reads from the port data register- To output, the 68HC11 writes into the port data register- All except port C have one data register:
PORTA (at $1000)PORTB (at $1004)PORTC (at $1003)PORTCL (at $1005)PORTD (at $1008)PORTE (at $100A)
6811 Parallel I/O Using Ports6811 Parallel I/O Using Ports
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-Each pin of ports C and D has an associated bit in a specific data register and another in a data direction register.
-The primary direction of a pin is set by its associated bit in the data direction register.- When an output pin is read, the value at the input to the pin driver is returned.
-The data direction registers are cleared by reset to configure all bi-directional I/O pins for input.
- Before performing I/O operation to these two ports, the software should set up the data direction registers of these two ports.
Data & Direction RegistersData & Direction Registers
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Display
4-bit Data
SourceP
O
R
T
C
0
3
4
7
0
0
0
0
1
1
1
1
DDRC
Data & Direction RegistersData & Direction Registers
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Which PORTCpins areInput:Output:?
Which PORTCpins areInput:Output:?
Eg: Setting I/O Pin DirectionsEg: Setting I/O Pin DirectionsPORTC Example Program FragmentPORTC Example Program Fragment
PORTC EQU $1003
DDRC EQU $1007
IO_PAT EQU %11110000
NUMBER EQU %10010011
...
LDAA #IO_PAT
STAA DDRC
LDAA #NUMBER
STAA PORTC
LDAA PORTC
[3:0][7:4]
What bit patternis output:?
What bit patternis output:?
%1001
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REGBAS EQU $1000PORTD EQU $08DDRD EQU $09
LDX #REGBASLDAA #$3F ; directions of port D pinsSTAA DDRD,X
LDAA #$CD ; output $CD to port DSTAA PORTD,X
Eg: Output to Port DEg: Output to Port D
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- All strobed mode I/O and handshake I/O are controlled by this PIOC register
Parallel I/O Control RegisterParallel I/O Control Register
7 6 5 4 3 2 1 0
STAF STAI CWOM HNDS OIN PLS EGA INVB
value after
reset0 0 0 0 0 U 1 1
STAF: Strobe A flag . This bit is set when a selected edge occurs on theSTRA signal.
STAI: Strobe A interrupt enable . When the STAF and STAI bits areboth equal to 1, a hardware interrupt request will be made to the
CPU.
EGA: Active edge for STRA0: falling edge1: rising edge
INVB: Invert STRB0: STRB active low1: STRB active high
PIOC
at $1002
. . .
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- Strobe is an external signal which can be used to trigger the I/O from the port.- Eg: Push botton !
Strobe Setup: -Strobe mode I/O selected when the bit 4 (HNDS) of the PIOC register is set to 0 and port C becomes a strobe input port.
-The bit 1 (EGA) of the PIOC register when set to 1 selects the active edge of the STRA pin.- The active edge of the STRA signal latches the values of the port C pins into the PORTCL register.
Strobe Input Port CStrobe Input Port C
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Strobe I/O Port C (Contd)Strobe I/O Port C (Contd)- Reading the PORTC register returns the current values
on the port C pins.- Reading the PORTCL register returns the contents of
the latched PORTCL.
- When enabled using bit 6 (STAI) of the PIOC, the active edge of the STRA signal will generate an interrupt to the 68HC11.
- This interrupt shares the same vector as IRQ.- This can be used to force an interrupt-driven I/O !
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Do Activity #1 NowDo Activity #1 NowReference code
REGBAS EQU $1000PORTD EQU $08DDRD EQU $09
LDX #REGBASLDAA #$3F ; directions of port D pinsSTAA DDRD,X
LDAA #$CD ; output $CD to port DSTAA PORTD,X
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Goal: Example TaskGoal: Example TaskRead the output of the 4-bit data source every time the push
button is pressed, and display the result.Read the output of the 4-bit data source every time the push
button is pressed, and display the result.
4-bit Data
Source
Push Button
Computer(HC11 chip)
Display
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Recap: Polling MethodRecap: Polling Method4-bit Data
Source
Push Button
Computer(HC11 chip)
Display
START
BUTTON PRESSED?
1 ms delay
BUTTON PRESSED?
READ 4-BIT INPUTUPDATE DISPLAY
NO
NO
YES
YES
This style of computerinput/output is called
Polled I/OPolled I/Obecause we’re constantly
polling the pushbutton
This style of computerinput/output is called
Polled I/OPolled I/Obecause we’re constantly
polling the pushbutton
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Recap: Interrupt MethodRecap: Interrupt Method
STARTINTERRUPT SERVICE
ROUTINE
READ THE 4-BIT INPUTUPDATE THE DISPLAY
RETURNFROM
INTERRUPT
START
INITIALIZE
DO SOMETHING
USEFUL
KeyPressed
The CPU is temporarily interrupted. An Interrupt Service Routine is entered
The CPU is temporarily interrupted. An Interrupt Service Routine is entered
The CPU now resumes where it left off!The CPU now resumes where it left off!
STARTINTERRUPT SERVICE
ROUTINE
READ THE 4-BIT INPUTUPDATE THE DISPLAY
RETURNFROM
INTERRUPT
DO SOMETHING
USEFUL
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Interrupt DetailsInterrupt Details
RETURNFROM
INTERRUPT (RTI)
START
Initialize StackSetup Interrupt Vectors
Clear previous interrupts & initialize device keeping
interrupts disabled
MAIN LOOP
STARTINTERRUPT SERVICE
ROUTINE
Further identify source if neededService interrupt
Clear interrupt request flag*
Enable interrupts locally at deviceEnable interrupts globally
Identify source(s)Resolve priorityPush registers
Disable further interruptsCall interrupt service routine
Restore registersEnable Interrupts
InterruptRequest
Done by hardware
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Task: Hardware SetupTask: Hardware Setup• The low nibble of PORTC is connected to a 7-segment
display (output)
• The hi nibble of PORTC is connected to a 4-bit thumbwheel switch (input)
• The STRA line is connected to a high-asserting pushbutton
• Problem :
– Copy thumbwheel setting to display whenever pushbutton is pressed.
– This program should run on the EVB
– Also illustrates the general form of programs using interrupts.
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Code: initializationCode: initialization*Equates: define symbolic names for registers and constantsPIOC EQU $1002PORTC EQU $1003DDRC EQU $1007PORTCL EQU $1005VECLOC EQU $00EE ; see EVB manual sec 3.3 the STRA line generates an IRQ interruptJMPOP EQU $7E ; opcode for extended jmpIOPAT EQU $0F ; for data direction regCTRPAT1 EQU %00000011 ; for PIOC reg, STAI disabledCTRPAT2 EQU %01000011 ; for PIOC reg, STAI enabled
* Data Section - setup stack space and initial Stack Pointer ORG $D000STACK RMB $7FFINITSP EQU *-1
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Code: Init Port CCode: Init Port C* Setup and Initialization Program
ORG $C000
* initialize stack pointer
SETUPINT LDS #INITSP
* initialize PORT C and associated control registers
LDAA #CTRPAT1 ; STAI (temporarily) disabled
STAA PIOC
LDAA #IOPAT ; $0F => lower nibble output
; higher nibble input
STAA DDRC
CLR PORTC ; Clear Port C
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Code: Setup Software IVTCode: Setup Software IVT*setup interrupt vector in Buffalo jump table.
*See section 3.3 of EVB manual for details.
LDAA #JMPOP ; Load the Opcode for JMP
; at this vector location
STAA VECLOC
LDX #ISRIRQ ; Load the 16-bit RAM Address ; for the IRQ ISR (which is ; shared by STRA) in the next ; 2 bytes.
STX VECLOC+1 ; Total:3 bytes per IVT location
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Code: Enable Interrupts; MainCode: Enable Interrupts; Main*clear status of peripheral or subsystem that could cause*an immediate interrupt. See 6811 Reference manual Section 5.7,* Also see the textbook. LDAA PIOC LDAA PORTCL* Enable Interrupt in peripheral or subsystem LDAA #CTRPAT2 ; STAI enabled
STAA PIOC* Enable Interrupts globally CLI ; Clears I-bit in CCR. 0 => enable* Jump to main program JMP MAIN******************************************************* MAIN PROGRAM: trivial******************************************************
MAIN BRA MAIN
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Interrupt Service RoutineInterrupt Service RoutineOn entry, all registers (incl. CCR with I bit) have been pushed on stack,
and the I bit is set to 1 to mask further interrupts. * First check for valid interrupt. Branch to RTIIRQ if invalid.
ISRIRQ LDX #PIOC BRCLR 0,X %10000000,RTIIRQ* Execute the unique recipe for clearing device interrupt flag
LDAA PIOC LDAA PORTCL ; Wacky !!* Service interrupt
RORA RORA
RORA ; Rotate 4 times RORA ; Low nibble now has the 4 bits!
STAA PORTC ; Output to 7-segment display* Return from interrupt service routine
RTIIRQ RTI ; restore registers and return to main* Note that this restores CCR (hence I bit), re-enabling interrupts.
END
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Do Activity #2 NowDo Activity #2 NowDue: End of Class Today.
RETAIN THE LAST PAGE(S) (#3 onwards)!!
For Next Class:• Bring Huang Textbook, & HC11 PRG
• Required Reading:– Sec 4.1-4.7 of Huang
• This reading is necessary for getting points in the Studio Activity!
