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AAA
BY SDH
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_Displaying System Date and Time_
Hello assemblers! Welcome to the 12th submission of
the AAA! This month we will cover quite a few new
tricks. We will learn a simple method on how to access
the system date and time and display this information
to the screen. We will also cover employing some
pre-supplied subroutines that AMOS provides for us, and
even learn how to access them during assembly. Let's
get started.
_Using a System Library Routine_
AMOS supplies us assemblers with some standard
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_library_ routines that we may access. One of these
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routines (think subroutine) will output the system date
and time for us, and is labeled _$ODTIM_ (_$_ystem call
_O_utput _D_ate and _TIM_e). Just as we have written short
subroutines in earlier AAA programs and then used "CALL
ROUTINE", we can _CALL $ODTIM_ - even though the library
routine's code is not contained within our program.
Remember in the December '86 AAA we created a
subroutine called MENU that typed out a menu to the
screen and waited for user input. When we accessed this
subroutine, we just placed in the code _CALL MENU_.
Further down in the code was our routine marked with
the label MENU:. This is how the assembler figured out
where to get the next instruction(s). When the MENU
routine was finished, we returned to the line below the
_CALL_.
When you use a library routine like $ODTIM, you still
have the line of code _CALL $ODTIM_, but you do _not_ have
a label $ODTIM:! AMOS will execute the code contained
in $ODTIM and then return you to your program. However,
how does AMOS know where to get the instructions
contained in $ODTIM? The procedure is twofold.
1) You must first place in a line of code at the top
of your program that looks like this: _AUTOEXTERN_. This
line informs the assembler that any CALL or LABEL that
it can't find from within the source code must exist
"externally". In other words, $ODTIM exists externally
to the file. Since there is some source code "missing",
the assembler cannot create a .LIT file (the dot
command). Therefore, the assembler only gets through
Phase 2 of assembly, and creates an .OBJ file.
2) To "link" up the external label or CALL with our
.OBJ file from (1) above, you use the _.LNKLIT_ command.
LNKLIT has many forms, but for library routines, the
format is _.LNKLIT object program name_. This command
will then take our .OBJ file from (1) above and link in
the external library code, creating our desired dot
(.LIT) command. Simple enough, no?
_Format of $ODTIM_
The subroutine $ODTIM has many different formats.
Again, this routine will display the date and time for
us, but the display has many different looks. Below is
the calling setup for $ODTIM. It requires registers D3,
D4, D5, and A2 to be set up according to the desired
format you would like to see the time and/or date
displayed:
_D3_ : if 0, use system time and system date, egnor D4.
If non-zero, D3 contains the date you would like
displayed.
_D4_ : if D3 is zero, D4 is egnored, else D4 holds the
time you would like displayed.
_D5_ : contains "flags" (set bits). Each of the first 16
bits (lower word) of D5 represent flags to dictate
$ODTIM's output (see the diagram below for each flags
purpose). A special case exists if D5 contains a "-1".
If D5 contains a -1, the output looks like this:
center Friday, February 20, 1987 02:15:53 PM
_A2_ : if non-zero, the date and/or time is returned to
the memory location pointed to by A2. If you do not
want the output to go to a memory location, make sure
A2 contains a zero.
;ED - INSERT FROM SUPER DAVES DOODLES "TIME BITS" HERE
_Time for an Example Program_
Let's employ the $ODTIM call in a simplified clock
program. Below is a program called CLOCK. This program
will display the current day to us and then continually
update the time of day. Here is CLOCK:
;ED, PROGRAM IS CALLED CLOCK.M68[300,7]
_Line-by-Line, Byte-by-Byte (partial)_
SEARCH AAA. This is a non-AMOS universal file that we
have been using over and over. This file contains all
of our slick MACROs that we have created over the
series. This universal file is in the Assembler PPN on
the Network [100,133] and is also listed in the
January '87 AAA. Once we SEARCH this file, we may use
any or all of the MACROs contained within.
;
AUTOEXTERN
This informs the assembler that there is some source
code external to this file, and LNKLIT will need to be
performed.
;
DEFINE CLEAR = PRTTAB -1,0
DEFINE CUROFF = PRTTAB -1,29.
DEFINE CURON = PRTTAB -1,28.
This is really slick. Since AAA.UNV from our SEARCH
above contains the MACRO "PRTTAB" (which is just like
PRINT TAB (#,#) from within BASIC), we can create "new"
MACROs by employing the already defined PRTTAB MACRO.
This is a very nice feature of the Alpha Micro
assembler, and it definately makes your programs really
easy to read.
;
CLR D3
MOV #0,A2
This is where we setup $ODTIM's input parameters. Since
D3 contains a zero, we will be using the current system
time and date (and D4 will be egnored). Also, since the
output will be to the terminal, A2 must contain a zero.
;
MOV #^H000002F6,D5
Move the 32 bit HEX value (#^H) 2F6 to register D5.
This is where we "set our flags". The binary equivalent
for HEX 2F6 is 00000000000000000000001011111010. This
flag setting will produce the following using $ODTIM
(assuming the date is 02/20/87):
center Friday, February 20, 1987
To see this, take the lower 16 bits of the above binary
equivalent and place these bits in the above diagram.
(If you are confused between binary, hex, and octal,
get a program called _CONVRT.BAS_ off the Network, PPN
[100,101]. This program lets you enter in any number
and see all the equivalents of every base. Also See the
November '85 Heyliger's Highlights).
;
CLEAR
CUROFF
PRTTAB 3,20.
TYPE <Today is >
The above four lines clear the screen, turn off the
cursor, tab to row 3, column 20, and type out the
message contained in the <..>. Notice how the 3 MACROs
above make for real easy programming!
;
CALL $ODTIM
Here is our library routine call. This will cause the
$ODTIM routine to be executed and then after execution,
AMOS will return control to our program on the next
line below this CALL.
;
PRTTAB 5,25.
TYPE <Current time is: >
CTC
These three lines will first move the cursor to row 5,
column 25, type out the message contained between the
<...>, and then "set" control C (just in case this
wasn't set before the user ran CLOCK).
;
CLR D3
MOV #H^00004801,D5
These two lines will set up $ODTIM to type out the time
to the users terminal in the following format:
center hh:mm:ss AM/PM
The HEX value 4801 has the 32 bit binary equivalent of
00000000000000000100100000000001. See if you can place
the lower 16 bits of this number into the diagram above
to understand the flag settings!
;
CTRLC BYEBYE
PRTTAB 5,42.
CALL $ODTIM
SLEEP #5000.
The above for lines are repeated over and over again
until the user hits a cC. The CTRLC line informs AMOS
to JMP to the label BYEBYE when a user hits a cC. The
PRTTAB line will place the cursor at the end of the
"Current time is: " line, then the $ODTIM call will
type out the time of day for us. The SLEEP instruction
will cause the JOB to sleep for 1/2 second, at which
time the above four lines will be executed again. The
only way out of this infinate loop is via cC.
;
CURON
CLEAR
EXIT
END
Finally, CURON will cause the cursor to be turned back
on, CLEAR will clear the screen, and EXIT will place
you back at the dot. END informs the assembler that
there is no more source code for this file.
_A Wrap_
Not bad! This assembly stuff is getting easier and
easier, isn't it? When you assemble this program,
remember that the assembler will only go through Phase
2 (assuming no errors). Once Phase 2 is complete, enter
in _.LNKLIT CLOCK_. This will create CLOCK.LIT. Remember,
you may order a compiled version of the first 10 AAA's
for only $10.00 via AMUS, so don't delay. Have fun with
CLOCK, and I'll see you next month or at AMUS '87.
