Compute Gazette - Commodore Computers

PEEKing Time
PEEKing Time
I own a Commodore 64, and I am just starting to
learn machine language. I have a question about
the time (TJ$) (TI$) function. What location in memory
do you look at to get the current value for the
T1 TI$ $ function?
Corey McKinnon
BASIC's time variables ([1$ alld TI) ra/llm tile CIITrelit
vallie of a blli/t·ill illterval timer.; PRINT TI re­
BASIC'S time variables (71$ and TI) return the cur
rent value of a built-in interval timer: PRINT TI re
fil turns ms a /IIul1cric numeric vallie value s/lOw;II8 showing the currellt current lilller timer
cOIlII1 count ill in jllcrcmcllts increments called jiffies, where olle one jiffy is
1/60secoud. second. Thus, to display the COlltellts contents of tile the
timer as seconds, you would fYl'C ti/pe PRl PRINT ~T TI/60.
71/60.
PRINT TIS 775 refllnls returns til thee vallie value of Tl TI tralls/aled
translated
;1110 into a strillg string of characters represelltillg representing the lime time ill in
hOllrs, hours, miml/es, minutes, (llId and seconds.
The illtcl1Ja/ interval tilller timer is [alllICI found at memory loealioll5
tions 160-162 (hex addresses $AO-$A2) SA0-SA2) ill in botll both tile the
loca
VIC and 64. Location 160 licks once every 1092 sec
ollds onds (65536 jiffies), locatioll location 161 ticks every 4.26
seconds secollds (256 jiffies), alld and 162 ticks every jiffy (sixty
times a second). BASIC determilles determines tile the vallie value of TI Tl
by performing the equivalent of:
VIC alld 64. Locatioll 160 licks alice every 1092 sec­
by performillg the eqllivalent of:
TI - I'EEK( 160) ° 65536 + PEEK( 161 )0 256 + l'EEK(162)
It th ell determilles the val lie of TIS fro m the vallie
It then determines the value of TI$ from the value
of TI, 71, so there are 110 no locatious locations which actually hold
the CIIrrellt current vallie value of TIS. Thai That is, there Ihere are 110 no locatiolls
tions ill in thee compllter computer holding Iioldillg the lim timee ill in hOllrsmil/lltes-secminutes-seconds
l/ds format. fomw You YOI/ call can read the clock from frolll macl/il/e machine lal/gllage
language
hours-
simply by examillillg examining tile the cOl/tel/ts contents of locations
160-162. 162. You can call also use lise the bllilt-ill built-in Kernal Ken/al ROM
rOl/lilles routines RDTIM (SFFDE) to read the clock or
SETTIM (SFFDB) to set it. See the e VIC or 64 Programmer's
Reference Guide for more details. However,
in il/ either case, you will have to do some
manipulating mal/ipllialillg if you want Wa/lt the e time tillle in ill seconds in illstead
of jiffies.
You YOII should be aware that thai the /Ire clock stops run rllI!-
ning 1Iillg during dllrillg tape SAVEs and LOADs. WADs. If you set the
clock and then eu perform one of these tape operations, operatiolls,
the time value will be incorrect.
th e time vall/e will be incorrect.
Disk Drive Device Number
Disk Drive Device Number
Change
I have two 1541 disk drives and want to change
the address of one of them via the hardware
method. I followed owed the instructions in the
owner's manual, but can't tell which wires are
the jumpers in question. Please help.
Nolan L. Green
The Tile instruction ;1Istmctioll manual's manllal's reference to jumpers might
be misleading. misieadillg. The Tile "jumpers" are actually two
round rOlllld disks of solder, each about 1/4 inch illell in ill diameter.
Each Eacll disk is separated into ill to halves, with witll a thin tlli"
strand stralld of solder sohler connecting cO llllectillg each half. llalf.
12 COMPUTE'S COMPUTE!", Gazorro GOtOl/1I September Scplembor 19fM 1984
U"plug tile power cord frolll til e wall and ope"
Unplug the power cord from the wall and open
tile the disk drive following llowillg tile the illstructions instructions in tile the
user's IIlmlllal. manual. 0" On tile the older (white case) model
1541s, til thee jllmpers jumpers are fo found 0on 1/ fil thee left edge of til thee
eire/lit circuit board, jllsf just behind tile the fOllg long plugs wii11 with wires.
01/ On th thee n(.'wer newer (tall (tan case) model 1541s, 1s, th they are arc fOl found llld
IIear near fhe the cellter center of ti,e the circuit board, toward ti,e the
frolli front. . 0On11 both models, jumper 1 is "earest nearest the front.
0" On tile the "ewer newer models, tlley they ca" can be found ulld i" in the middle
toward
ti,e the front. fro"t.
0" the older 1541, tile ju.mpers are all the left edge, to
ti,e rca r.
On the older 1541, the jumpers are on the left edge, to
the rear.
Challging the dev ice 1llimbers is accomplished by
Changing the device numbers is accomplished by
taking a sharp, pointed pail/ted object and scratching scratelling away
the e thin til strand of solder connecting comlec/illg the tile two halves
on one or both of the jumpers. Do this til is very care
re·
fully flilly so as not II0t to damage the til e circuit it board or any allY
other of /l er components.
cO II/pol/ellts.