BIT TEST AND BRANCH INSTRUCTIONS. These instructions use direct addressing mode to specify the location being tested and relative addressing

Instruction Branch if Carry Clear Branch is Carry Set Branch if Equal

Branch if Half-Carry Clear Branch if Half-Carry Set Branch if Higher

Branch if Higher or Same Branch if Interrupt Line is High Branch if Interrupt Line is Low Branch if Lower

Branch if Lower or Same

Branch if Interrupt Mask is Clear Branch if Minus

Branch if Interrupt Mask Bit is Set Branch if Not Equal

Branch if Plus Branch Always

Branch if Bit n is Clear Branch if Bit n is Set Branch Never

Branch to Subroutine

Mnemonic BCC BCS BEQ BHCC BHCS BHI BHS BIH BIL BLO BLS BMC BMI BMS BNE BPL BRA BRCLR BRSET BRN BSR

3.4.5.7 BIT TEST AND BRANCH INSTRUCTIONS. These instructions use direct addressing mode to specify the location being tested and relative addressing to specify the branch destination. This applications guide treats these in-structions as direct addressing mode inin-structions. Some older Motorola doc-uments call the addressing mode of these instructions BTB for bit test and branch.

3.4.5.8 INSTRUCTIONS ORGANIZED BY TYPE. Tables 3-2 through 3-5 show the MC68HC05 instruction set displayed by instruction type.

MOTOROLA M68HC05 MICROCONTROLLER APPLICATIONS GUIDE 3-35

w

-Table 3-2. Register/Memory Instructions

Addressing Modes

Direct Extended Indexed Indexed Indexed

(No Offset) (8-Bit Offset) (16-Bit Offset)

o ~

Table 3-3. Read/Modify-Write Instructions

Addressing Modes

Table 3-4. Branch Instructions

Relativ~ Addressing Mode

Function Mnemonic # #

Opcode Bytes Cycles

Branch Always BRA 20 2 3

Branch Never BRN 21 2 3

Branch IFF Higher BHI 22 2 3

Branch IFF Lower or Same BLS 23 2 3

Branch IFF Carry Clear BCC 24 2 3

Branch IFF Higher or Same

BHS 24 2 3

(Same as BCC)

Branch IFF Carry Set BCS 25 2 3

Branch IFF Lower

BLO 25 2 3

(Same as BCS)

Branch IFF Not Equal BNE 26 2 3

Branch IFF Equal BEQ 27 2 3

Branch IFF Half-Carry Clear BHCC 28 2 3

Branch IFF Half-Carry Set BHCS 29 . 2 3

Branch IFF Plus BPL 2A 2 3

Branch IFF Minus BMI 2B 2 3

Branch IFF Interrupt Mask Bit is Clear BMC 2C 2 3

Branch IFF Interrupt Mask Bit is Set BMS 2D 2 3

Branch IFF Interrupt Line is Low BIL 2E 2 3

Branch IFF Interrupt Line is High BIH 2F 2 3

Branch to Subroutine BSR AD 2 6

3-38 M68HC05 MICROCONTROLLER APPLICATIONS GUIDE MOTOROLA

Table 3-5. Control Instructions

Inherent

Function Mnemonic # #

Opcode Bytes Cycles

Transfer A to X TAX 97 1 2

Transfer X to A TXA 9F 1 2

Set Carry Bit SEC 99 1 2

Clear Carry Bit CLC 98 1 2

Set Interrupt Mask Bit SEI 9B 1 2

Clear Interrupt Mask Bit CLI 9A 1 2

Software Interrupt SWI 83 1 10

Return from Subroutine RTS 81 1 6

Return from Interrupt RTI 80 1 9

Reset Stack Pointer RSP 9C 1 2

No-Operation NOP 9D 1 2

Stop STOP 8E 1 2

Wait WAIT 8F 1 2

MOTOROLA M68HC05 MICROCONTROLLER APPLICATIONS GUIDE 3-39

3.4.6

Instruction Set Summary

3-40

Computers use an operation code or opcode to give instructions to the CPU.

The instruction set for a specific CPU is the set of all opcodes that the CPU knows how to execute. The CPU in the MC68HC705C8 MCU can understand 62 basic instructions, some of which have several variations that require separate opcodes. The M68HC05 instruction set includes 210 unique instruc-tion opcodes.

The following table is an alphabetical listing of the M68HC05 instructions available to the user. In listing all the factors necessary to program, the table uses the following symbols:

H

means the contents ffi of memory location

M68HC05 MICROCONTROllER APPLICATIONS GUIDE MOTOROLA

INSTRUCTION ADDRESSING MODES, AND EXECUTION TIMES (Sheet 1 of 4)

Branch if Carry Clear Clear Bit n in Memary

Branch if Carry Set Branch if Equal Branch if Half Carry Clear Branch if Half Carry Set

Operand Opcode Operand IMM

M68HC05 MICROCONTROLLER APPLICATIONS GUIDE

Bytes Cycles Condition Code H I N Z C

INSTRUCTION ADDRESSING MODES, AND EXECUTION TIMES (Sheet 2 of 4)

Source Boolean Addressing Machine Coding

Operation Mode for (hexadecimal) Bytes Cycles Condition Code

Form(s) Expression

3-42 M68HC05 MICROCONTROLLER APPLICATIONS GUIDE MOTOROLA

INSTRUCTION ADDRESSING MODES, AND EXECUTION TIMES (Sheet 3 of 4)

Source Boolean Addressing Machine Coding

Operation Mode for (hexadecimal) Bytes Cycles Condition Code

Form(s) Expression

MOTOROLA M68HC05 MICROCONTROLLER APPLICATIONS GUIDE 3-43

INSTRUCTION ADDRESSING MODES, AND EXECUTION TIMES (Sheet 4 of 4)

Source Addressing Machine Coding

Operation Boolean

Mode for (hexadecimal) Bytes Cycles Condition Code

Form(s) Expression

-3-44 M68HC05 MICROCONTROLLER APPLICATIONS GUIDE MOTOROLA

3.4.7 Interrupts

Systems often require that normal processing be interrupted so that some external event may be serviced. The MC68HC705C8 may be interrupted by one of five different methods: anyone of four maskable hardware interrupts (IRQ, SPI, SCI, or timer) and one nonmaskable software interrupt (SWI). In-terrupts such as timer, SPI, and SCI have several flags which will cause the interrupt. Generally, interrupt flags are located in read-only status registers;

their equivalent enable bits are located in associated control registers. The interrupt flags and enable bits are never contained in the same register. If the enable bit is a logic zero, it blocks the interrupt from occurring but does not inhibit the flag from being set. Reset clears all enable bits to preclude interrupts during the reset procedure.

The general sequence for clearing an interrupt is a software sequence of first accessing the status register while the interrupt flag is set, followed by a read or write of an associated register. When any of these interrupts occur and the enable bit is a logic one, normal processing is suspended at the end of the current instruction execution.

Figure 3-8 shows how interrupts fit into the normal flow of CPU instructions.

Interrupts cause the processor registers to be saved on the stack and the interrupt mask (I bit) to be set to prevent additional interrupts. The appropriate interrupt vector then points to the starting address of the interrupt service

MOTOROLA M68HC05 MICROCONTROLLER APPLICATIONS GUIDE 3-45

w ~

Bit Mani~ulation Branch

BTB BSC REL

M68HC05 Instruction Set Opcode Map

Read/Modifv/Write Control

Bit Test and Branch MNEMONIC

Indexed (No Offset) BYTES

Indexed, 1 Byte (8-Bit) Offset

Indexed,2 Byte (16-Bit) Offset CYCLES

ReQister/Memorv I

routine (refer to Figure 3-9 and Table 3-6 for vector location). Upon completion of the interrupt service routine, the RTI instruction (which is normally the last instruction of the routine) causes the register contents to be recovered from the stack followed by a return to normal processing.

NOTE

The interrupt mask bit (I bit) will be cleared if, and only if, the cor-responding bit stored in the stack is zero.

Table 3-6. Vector Address for Interrupts and Reset

Register Flag

Interrupts CPU Vector

Name Interrupt Address

N/A N/A Reset RESET $1 FFE-$1FFF

N/A N/A Software SWI $1FFC-$1FFD

N/A N/A External Interrupt -IRQ $1 FFA-$1 FFB

Timer Status ICF Input Capture TIMER $1 FFS-$1FF9

OFC Output Compare TOF Timer Overflow

SCI Status TDRE Transmit Buffer Empty SCI $1 FF6-$1FF7

TC Transmit Complete RDRF Receiver Buffer Full

IDLE Idle Line Detect

OR Overrun

SPI Status SPIF Transfer Complete SPI $1FF4-$1FF5

MODF Mode Fault

Reset and interrupt operations are often discussed together because they share the common concept of vector fetching to force a new starting point for further CPU operation. Unlike interrupts, there is no intention to ever return to whatever the CPU was doing before a reset occurred.

A low on the RESET ir)put pin causes the program to vector to its starting address specified by the contents of memory location $1 FFE and $1 FFF. The I bit in the condition code register is also set. Much of the MCU is configured (forced) to a known state during reset.

3.4.7.1 SOFTWARE INTERRUPT (SWI). The software interrupt is an executable instruction. The action of the SWI instruction is similar to the hardware in-terrupts. The SWI is executed regardless of the state of the interrupt mask (I bit) in the condition code register. The interrupt service routine address is specified by the contents of memory location $1 FFC and $1 FFD.

MOTOROLA M68HC05 MICROCONTROLLER APPLICATIONS GUIDE 3-47

3-48

YES

YES

YES

CLEAR IRQ REQUEST LATCH

LOAD PC FROM VECTOR:

IRQ: $1 FFA, $1 FFB TIMER: $1 FF8, $1 FF9

SCI: $1 FF6, $1 FF7 SPI: $1FF4, $1FF5

RESTORE REGISTERS

FROM STACK t---~

CC,A, X, PC

Figure 3-8. Hardware Interrupt Flowchart

M68HC05 MICROCONTROLLER APPLICATIONS GUIDE MOTOROLA

STACK

TOWARD LOWER ADDRESSES (LOWEST STACK ADDRESS IS $OOCO)

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