Commodore PET - Page 295

The PET also keeps track of time in "jiffies". A "jiffy" is 1/60 of a sec-
ond. Reserved numeric variable TIME. or TI. is a numeric variable which is auto-
matically incremented every
1/60 of a second. TIME is initialized to zero on start-
up. and is reset back to zero after 51.839.999 jiffies. TIME$ (hhmmss) is a string
variable that
is generated from TIME. To ensure greater accuracy the PET
keeps track of time
in jiffies by incrementing every 1/60 of a second, instead
of once every second. When
TIME$ is called to print the time in hours,
minutes, and seconds, the memory converts
jiffy time to real time. Notice
that TIME$ and TI$
are not the string conversion of TIME and TI but are numbers
representing real time calculated from jiffy time
(TIME. TI). The conversion is done
as follows. Each second is divided into 60 jiffies. One minute is composed of 60
seconds. One hour
is made up of 60 minutes. In summary. one second is 60 jiffies.
one minute
is 3600 jiffies. and one hour is 216.000 jiffies. as illustrated below:
Jiffy = 1
= 60 x Jiffy
= 60 Jiffies
Minute = 60 x Second
= 60 x (60 Jiffies)
= 3600 Jiffies
Hour
= 60 x Minute
= 60 x (3600 Jiffies)
= 216.000 Jiffies
S,",\J;IIY
M;O"\S,,,Odl60 = J;lIy
Hour/60 = Minute/60 = Second/60 = Jiffy
The following equations convert jiffy time (J) into real time divided into
hours
(Hl. minutes (Ml. and seconds (S). We can write a program to print the time
from jiffies.
282
le ~T=TI
213 H=INT<J/216eee)
313 IF H<>e THEN J=J-H~2160e
41:::1 ,..1= l NT (.J /3613(1)
513 IF M<>e THEN J=J-M~36ee
Calculate hours.
Integer function takes only whole
number.
If any hours. subtract number of
jiffies in one hour by H to leave
remaining jiffies.
Calculate minutes.
Integer function takes only whole
number.
If any minutes. subtract number of
jiffies in minutes by 7 to leave
remaining jiffies.
Calculate seconds. Integer function
takes only whole number.