# Polling, rather than push

# push $($using interrupts$)$ on Tuesday.

#Hexadecimal keyboard

# Byte value at address $0$xFFFF$0012$ : command row number of hexadecimal keyboard

$($bit $0$ to $3)$

# and enable keyboard interrupt $($bit $7)$

# Byte value at address $0$xFFFF$0014$ : receive row and column of the key pressed, $0$

if not key pressed

# The mips program have to scan, one by one, each row $($send $1,2,4,8...)$ and then

observe if a key is

# pressed $($that mean byte value at adresse $0$xFFFF$0014$ is different from zero$).$

This byte value is

# composed of row number $(4$ left bits$)$ and column number $(4$ right bits$)$ Here you'll

find the code for

# each key :

$0$x$11,0$x$21,0$x$41,0$x$81,0$x$12,0$x$22,0$x$42,0$x$82,0$x$14,0$x$24,0$x$44,0$x$84,0$x$18,0$x$28,0$x$48,0$x$88.$

# For exemple key number $2$ return $0$x$41,$ that mean the key is on column $3$ and row $1.$

# If keyboard interruption is enable, an exception is started, with cause register

bit number $11$ set.

# So$...$ we print a lot of crap... How can we change our program to only print a

value when change happens.

# Wait... CSC$120,$ A program that tracks change of state.. What kind of programs

did you study in CSC$120?$