Rambles by Stephen Shaw
RAMBLES by Stephen Shaw 1987
Hello again. Thanks to those of you who wrote in - but still no requests for articles on TI Basic or even Extended Basic, so it seems our readers have no interest in that area.
How did you fare in the telephone strike? Here in Manchester, we were hit a week earlier than the rest of the country and it dragged on a few days after as well. The result was a considerable decline in the number of lines into Manchester, leading initially to a false 'engaged' signal, and later on to a deep-space type sound! Unfortunately operators outside Manchester did not seem to know of our problems...
This will appear before the big meeting in May, so let me just say- I'll be there, British Rail permitting. I won't be doing any disk copying or selling or anything, just milling around... and I'll wear a neat little name badge too! Hope to make it for lpm.
Farewell to John Rice, leaving us for Amstrad Country. Hope your Amstrad will last as long as my TI console after your new Amstrad has been repaired that is...
Good old days
As one of the original UK owners of a TI99/4, I shall continue to use my TI99/4A for QUITE some time. (update: Actually kept in daily use until 1995 and regular use for another couple of years after that. Still in good working order in 2012 (30 years old!) although the disk drives really need lubrication. In 2014 the memory card failed (after 34 years), which restricted matters a bit, but only a bit!Other computers may be more powerful, but inevitably need more programming time to make them perform their tricks. And I like to program, not just use purchased programs! My programming has by no means exhausted the capabilities of my TI yet. Thank you to everyone who has helped ME to discover some of the secrets of the TI - irritating questions have often driven me to explore some dim dark alley to find surprising fruits! Hope to see you in Derby!
Scratch pad ram
"Where is scratch pad ram?" - Scratch pad ram is the ONLY area of ram addressed with a 16 bit data line. It is FAST. It can be found from >8300 to >83FE, and parts of it are used by the operating system. (Note: The symbol > means the number following is in hexadecimal format).Different bits are used depending on how you are using the console! In case you thought EASY BUG was part of the Mini Memory module- yes, it is in the module, but it does not RUN from there- for greater speed it is transferred to the scratch pad area, where it resides from >8370 to >83FF
>8300 to >8348 IS USED BY BASIC (XB) and so seems to be a reasonable place to put a pure machine code utility.
>834A to >83FE seems to be fully utilised for most environments.
TI Basic and OR and AND
'I know how IF (R=2)+(B=4) THEN works, but what does IF (A=2)+(R=4)=-2 THEN... mean...'This one goes back to the pioneering work of Pete Brooks in the early days...
IF... THEN... can be considered to take the form:
IF NOT ZERO THEN...ELSE IF ZERO THEN...
So: IF A THEN 100 will go to 100 if A has any value other than zero.
The computer treats an equals sign in a LOGICAL manner, treating the result as zero or minus one.
So, 2=2 is TRUE, and takes a value MINUS ONE
4=2 is NOT TRUE and takes a value of ZERO
Now look at the question again
IF A=2 the value of this equate is: -1
IF R=4 the value of this equate is: -1
And the sum of these is: -1+-1 = -2
What if one at the statements is untrue? Then one equates will be minus one, and the other will he zero, which adds up: 0 + -1 = -1
Therefore, the formula: (A=2)+(R=4) will have a non-zero value if EITHER of the equates is true, OR if both of them are true.
The plus sign can be thought of as OR
IF A=2 OR R=4 THEN..., which will carry out the transfer if either or both conditions are met.
If however we wish to transfer control only if both conditions are let, we need an equivalent to AND:
IF A=2 AND R=4 THEN
Try: IF (A=2) * (R=4) THEN
If both are true: -1 * -1 = +1 (non zero)
If only one is true: -1 * 0 = 0
Problem solved
So what of that strange form we started with?
IF (A=2)+(R=4)=-2 THEN
IF BOTH are TRUE the answer is -2 as we have seen!
If ONE is true, the answer is -1
If NONE are true the answer is ZERO..
Therefore this oddball form is another way of saying AND! I cannot think of any reason for preferring this form to the use of the multiply (asterisk) sign.
Machine Code for Extended Basic
MACHINE CODE:
Graham Marshall sent me two machine code utilities for Extended Basic to share with you through Rambles.
The first is a STRING ARRAY SEARCH.
Take an array A$() with 30 elements, and you want to find out which element has the word "RAMBLES" in it.
In extended basic you would use:
100 FOR T=1 TO 30
which all takes time - especially if the string array has many more elements and the word we are looking for is at the end. Using Graham's utility we would enter:
110 IF A$(T)="RAMBLES" THEN 150
120 NEXT T
130 PRINT "RAMBLES NOT FOUND"
140 STOP
150 PRINT "ELEMENT ";T;"HAS IT"
160 END
100 CALL LINK ("SEARCH",A$(),"RAMBLES",T)
All much faster
110 IF T>0 THEN PRINT "ELEMENT";T;"HAS IT"
120 END
130 PRINT "RAMBLES NOT FOUND"
140 END
I did have a little problem using this routine at first - it treats a null element as a marker for the end of the array, and I filled the array, leaving no nulls! (a null string is ""). The result was a BAD SUBSCRIPT error. The final element must be empty!
The routine is listed below in several formats
1. Source code For XB, Ed/As or Myarc ExBas
2. As CALL LOADS for those of you without a disk drive
3. The object code as a text file if you prefer to key it in with TI WRITER - remember to save this with the PRINT FILE option, using the option F to save it in FIXED 80 format!
Webnote: Accursed 1980's dot matrix numbers and letters do not OCR well in isolation, and manually retyping pages of them allowed many opportunities for error. So- I will give here the 9900 Assembly Code, just a short sample of the CALL LOAD format, and an IMAGE (png) of the DF80 format for interest
.
and to conclude, finally, there will be a demonstration program!
********************* **************
* SEARCH ROUTINE IN EXTENDED BASIC *
* FORMAT-CALL LINK("SEARCH",ARRAY, *
* STRING,VARIABLE) *
* ******************* ***************
DEF SEARCH
***************************
* FOLLOWING LINES ARE FOR *
* TI EXTENDED BASIC ONLY *
****************************
NUMASG EQU >2008
STRREF EQU >2014
XMLLNK EQU >2018
*****************************
* IF YOU ARE USING ED/AS OR *
* MYARC EX BAS THEN INSTEAD OF *
* THE ABOVE THREE EQUATES YOU MUST USE *
* REF NUMASG,STRREF,XMLLNK *
********************* *****************FAC EQU >834A STATUS EQU >837C CIF EQU >20
****************** *****************
* FOR ED/AS USE REPLACE THE ABOVE LINE WITH
* CIF EQU >2300 *
****************** *****************
COUNT DATA 0
STR1 BYTE 255
* ARRAY STORAGE
BSS 255
STR2 BYTE 255
* STRING STORAGE
BSS 255
EVEN
MYREG BSS 32
RTRN DATA 0
SEARCH MOV R11,@RTRN
LWPI MYREG
LI R0,0 * MOVE STRING TO BUFFER IN RAM
LI R1,2 * STRING IS 2nd PARAMETER PASSED
LI R2,STR2
BLWP @STRREF
LOOP LI R1,1 * MOVE STRING ARRAY TO BUFFER IN
INC R0 * RAM
LI R2,STR1
LI R3,255
SWPB R3
MOVE R3,@STR1
BLWP @STRREF
MOV @STR1,R4 *COMPARE THE STRING TO THE ARRAY
SWPB R4 *STRING
ANDI R4,>00FF
MOV R4,@COUNT * SET R4 TO LENGTH OF CURRENT ARRAY ELEMENT
CI R4,0 * IS LENGTH ZERO?
JNE CONT * IF THE ELEMENT IN THE STRING
CLR R0 * IS "" THEN FINISH
JMP FINISH
CONT LI R1,-1 * TRY SETO R1 INSTEAD OF LI, R1,-1
LOOP1 INC R1
MOVB @STR(R1),R2
MOVB @STR2(R1),R3
CB R2,R3
JNE LOOP * IF NOT EQUAL GET NEXT ARRAY STRING
C R1,@COUNT
JNE LOOP1 *COMPARE NEXT TWO CHARACTERS IN THF STRING
FINISH MOV R0.@FAC
BLWP @XMLLNK
DATA CIF *WRITE TO THE NUMERIC VARIABLE
LI R0,0
LI R1,3 *SEND RESULT OUT TO THIRD PARAMETER IN CALL
BLWP @NUMASG
CLR R0 * DOES IT MATTER IF YOU OMIT THIS
MOVB R0,@STATUS
LWPI >83E0
MOV @RTRN,R11 *RETURN TD XB
RT
END
Assemble with R option only for TI ExBas! Myarc ExBas can handle C option as well.
In CALL LOAD form to RUN in Extended Basic:
1 REM SEARCH ARRAY UTILITY B
Webnote: This goes on for another page but that is an awful lot of numbers to be retyped, with a lot of room for error, so I'll restrict it to this incomplete excerpt to show what the format was. I could place an image of the page up if there was an interest!
Y GRAHAM MARSHALL
2 REM REQUIRES XB + 32K RAM
USE: CALL LINK("SEARCH",ARRA
Y$(),FIND$,ELEMENT)
100 CALL INIT
110 CALL LOAD(16376,83,69,65
,82,67,72,39,24)
120 CALL LOAD(8194,39,158,63
,248)
130 CALL LOAD(9460,0,0,255,0
,0,0,0,0,0,0,0,0,203,53,203,
78,203,231,204,71)
140 CALL LOAD(9482,204,150,2
04,228,205,29,205,75,205,96,
33,131,35,253,38,184,40,183,
41,182,42,195)
150 CALL LOAD(9504,43,193,44
,179,45,194,47,196,58,181,59
,180,60,191,61,190,62,192,94
,197,255,58)
160 CALL LOAD(9526,58,130,65
,84,240,71,79,133,73,70,132,
79,78,155,79,82,186,80,73,22
1,84,79)
The concept of typing in a machine code routine in DF80 format with TI Writer is cute, so I will present an image of the single page of the object code routine. Here is a small thumbnail image- click the image for an image somewhat larger.
webnote: Be careful to spot the difference between the letter B and the number 8 - there isn't a huge amount of difference but the B has a straighter left side. The numbers at far right should be keyed in as they appear with the text using the full 80 columns.
Remember to save this using PF then eg F DSK1.SEARCH (where the F tells TI Writer to save the file as Display Fixed 80 instead of the default Display Variable 80 format).
How to use the object code file (A DF80 file DSK1.SEARCH) input as above or produced with Editor Assembler?
100 DIM STRING$(20)
110 CALL PEEK(12000,A) :: IF A=1 THEN 140
120 CALL INIT :: CALL LOAD("DSK1.SEARCH")
130 CALL LOAD(12000,1)
140 FOR A=1 TO 14 :: READ ST
RING$(A) :: NEXT A
150 CALL LINK("SEARCH",STRIN
G$(),"SPIDER",A) :: PRINT "A
RRAY ELEMENT ";A
160 DATA DOG,CAT,HORSE,LION,
TIGER,DEER,OTTER,SPIDER,WREN
,ANT,FLY,BAT,PENGUIN,BEAR
170 END
(webnote: The next code from Graham was to detect when a sprite coincided with an "on" pixel on the screen - but again it is a lot of manual error strewn retyping. I can email or post images if there is an interest)
