INITIALIZATION AND PROGRAMMING EXAMPLES
M68HC16 Z SERIES
E-18
USER’S MANUAL
JSR SEND_CH ;go send out the byte
AIX #$01 ;increment IX to point to the next byte
BRA SEND_STRING ;loop back and do next byte in string
STRING_DONE:
JSR DELAY ;wait for a moment
RTS ;go back to whence we came
SEND_CH: ;subroutine to send out one byte to SCI
LDAA SCSR ;read SCI status reg to check/clear TDRE bit
ANDA #$01 ;check only the TDRE flag bit
BEQ SEND_CH ;if TDR is not empty, go back to check it
;again
LDAA #$00 ;clear A to send a full word to SCDR ($FFC0E)
STD SCDR ;transmit one ASCII character to the screen
LOOP5: LDAB SCSR+1
ANDB #$80 ;test the TC bit (transfer complete)
BEQ LOOP5 ;continue to wait until TC is set
RTS ;return to send_string subroutine
***** The STRINGs *****
STRING DC 'The System Clock is now running at 16.777 MHz...',0a,0d,00
SEC_STR DC 'check this out!',0a,0d,00,00
STRING2 DC 'The System Clock is now running at 4.194 MHz...',0a,0d,00
***** Interrupts/Exceptions *****
BDM: BGND ;exception vectors point here
;and put the user into background debug mode
E.2.1.4 Example 4 - Software Watchdog, Periodic Interrupt, and Autovector Demo
* Description : This program demonstrates the software watchdog,
* the periodic interrupt, and an autovector.
* The periodic interrupt runs a clock which is updated
* on the dummy terminal. Every eight seconds the COP
* will force a reset unless IRQ6 is grounded. When IRQ6
* is pulled low, an autovectored interrupt routine will
* “feed” the watchdog with $55 and $AA, and the
* clock will run without being reset on the dummy terminal.
*
*********************************************************************
INCLUDE 'EQUATES.ASM' ;table of EQUates for common registers
INCLUDE 'ORG00000.ASM' ;initialize reset vectors
INCLUDE 'ORG00008.ASM' ;initialize interrupt vectors
ORG $002C ;put address of autovector routine
DC.W AUTOV ;at the level 6 vector (IRQ6)
ORG $0070 ;put address of periodic interrupt routine
DC.W VECRT ;at 1st user defined interrupt vector
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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