EE3376 – Embedded Systems - Fall 2007 - Exam 2 – MacDonald – Page 1
Student Name:_______________________________ Student ID: _______________
Problem 1
A section of the main program is running shown below and is in the middle of
executing the inx instruction when a RTI periodic interrupt occurs. The ISR is
shown in below as well and is a contrived example. Fill out the table describing
register and memory values at different points throughout the sequence
MAIN CODE ISR
---------------------------------------- ----------------------------------
rti_isr: ldy A, X
inca iny
inx IRQ occurs here inca
ldy A, X sty A, X
rti
Table 1
Location Prior to INCA Just after INX
Just after RTI Just after LDY
reg A $0F
reg B $08
reg D
reg X $1FF0
reg Y $0000
Mem $2000 $12
Mem $2001 $34
Mem $2002 $56
Mem $2003 $78
