Table of Contents
35 Forth Words as First Entry Application
( part of the eBook A Start With Forth published by Juergen )
Try it out – no installation needed, showing the final result of what is described here.
Write a simple Application using just 35 Forth Words.2) Set IO Bits and start a
COUNTER. There is a Word for
SOS as well; dependent on the hardware you can hear the
SOS as some sounds (or not) just try
VFXTESTAPP running on the PC. Change the
NAME word to display your NAME.
Runs under VFX, tested on FORTH INC Swiftforth, WIN32 and GFORTH, should run on Tablet and Mobile as well using the right GFORTH APP.
First install VFX430LITE from the mpeforth.com website. Next set up a folder C:\VFXTESTAPP. Store file vfxtestapp.fs into this folder. Start VFX430LITE. VFX will complain “cannot open comms” , just type <ok>, this is for later. Now open under Utilities → Forth Console. Forth is ready and running in the VFX Debug Console. Then copy
INCLUDE C:\VFXTESTAPP\VFXTESTAPP.fs into the VFX window and hit <cr>3) to run this demo. It might work as well, just to select all of the text in the open editor .fs window, copy and paste it into VFX Debug Window. See how VFX compiles to learn new words. When finished, type <cr> and then type
COUNTER. A few lines of “GUI” will be shown. Type in
PWL <cr>, changes PW from 1 to 0, or modify other bits. Enter
COUNTER <cr> again, or
400 SCOUNTER, or
???? <cr> for the little debugger. You get:
This is the virtual IO implementation of the MicroBox (see links further down), which consists of a Micro, PWM LED, 3 Switches, 4 OUT LEDs, 4 IN LEDs. Here shows some of this functionality in SW: no chip, no LEDs, no resistors, no PCB, no soldering, execute it on the PC only. Modify the code as exercise, change times, send other code than SOS and more.
This “GUI”4) is implemented using two very simple words -
PAGE to clear screen,
.“ to type text lines.
LINE1 shows the funtions, and
LINE2 the 1 bit PWM, 3 bits SWITCHES, 4 bits OUT, 4 bits IN, 4 bits ANI - 16 bits. Further down find the Word
MBV2, it prints the 16 Bits underneath this text. All lines are resent whenever one of the 16 bits have been changed/updated.
LINE2 shows the words that control the single bits, e.g. PWH and PWL.
???? shows the Variables and 8 positions of the data stack. Mark the bottom of the stack by entering
FFFF <cr> - leaves 7 possible stack locations.
This has been intentionally written by just using simple words and constructs, so anybody can use it as startig point. And as with all Forth programs, this application can be easily modified and extended – as it all can be done interactively.
Definitions for GUI
All of the numbers are understood as hexadecimal. The word
HEX does the magic. The LINES n print a small GUI, very basic, with
HEX : LINE1 ." \ VFXTESTAPP - bit change ie. PWH / PWL <cr>, try COUNTER, 400 SCOUNTER, SOS, ???? plus <cr> ExMark Oct2016" CR ; : LINE2 ." \ PWHL T3HL T2HL T1HL O3HL O2HL O1HL O0HL I3HL I2HL I1HL I0HL A3Hl A2HL A1HL A0HL h/l ???? " CR ; : LINE3 ." \ PWM T3___T2___T1 O3___O2___O1___O0 I3___I2___I1___I0 A3___A2___A1___A0 " CR ; : LINE4 ." X t t t o o o o i i i i a a a a " CR ; \ display after START? : TEST PAGE LINE1 LINE2 LINE3 LINE4 ( LINE5 ) CR ; \ display lines of our GUI Graphic User Interface, LINE5 not used
Variable PWM ( 0 or 1 ) \ not used for now, as combined in Variable PSWI Variable SWI ( Switches SW3 SW2 SW1 0 0 0 ) \ not used for now, as combined in Variable PSWI Variable PSWI ( PSWI X t t t 4 bits PWM and 3 Switches ) \ combines the bit for PWM and the 3 bits for the 3 switches Variable OUTP ( OUTP 3 2 1 0 7 6 5 4 of the 8 bits ) \ the 4 "OUTPUT LEDs" of the MicroBox Variable IN ( IN 3 2 1 0 3 2 1 0 of the 8 Bits ) \ 4 Input bits that can be set e.g. for AND OR XOR INVERT Variable ANI ( ANI 3 2 1 0 4 more bits for test ) \ either as simulated external ANALOG - or free for anything Variable HOU ( OUT as hexadecimal number 0 to F ) \ to be implemented, just showing the 4 OUT bits in hexadecimal Variable ALL ( PWM SWI OUT INP ANI ) \ To be done, combining it all into one 16 bit Variable
The Forth Program Code
: disbit4 DUP $8 AND IF ." 1" ELSE ." 0" THEN ; \ test a bit, here the topmost bit3 of the 4. If 1 then display 1, else 0 : ds Disbit4 1 LSHIFT ; \ display a bit, shift the 4 bits left by one, so bit 2 is the topmost and so on : dssp ds Space Space space space ; \ combine a bit with 4 Spaces, to be a block for display : 4dssp dssp dssp dssp disbit4 drop ; \ now combine all 4 bits of the Variable nibble, DROP cleans up the stack : DV 3 spaces PSWI @ 4dssp 4 spaces OUTP @ 4dssp 4 spaces IN @ 4dssp 4 spaces ANI @ 4dssp ; \ combine 4x 4 = 16 bits : SPACES ( u -- ) 0 ?DO SPACE LOOP ; \ define SPACES, often included in the Forth word set already : MBV2 PAGE LINE1 LINE2 LINE3 LINE4 DV CR ; \ MBV2 updates the “SCREEN”, first the explaining lines, then the 16 Bits : COUNTER Begin outp @ 1+ outp ! 300 ms mbv2 key? until ; \ run a counter program, see OUT bits change, type counter <cr> : SCOUNTER Begin dup outp @ 1+ outp ! ms mbv2 key? until ; \ the same with programmable speed, for example 400 scounter <cr> : SOS 07 emit 100 ms 07 emit 100 ms 07 emit 600 ms 07 emit 300 ms 07 emit 300 ms 07 emit 600 ms 07 emit 100 ms 07 emit 100 ms 07 emit ; : LINE5 ." PSWI OUT IN ANI - R0 R1 - Stack contents " CR ; \ description of ???? display
: ???? 3 spaces PSWI @ . OUTP @ . IN @ . ANI @ . 4 spaces >R >R >R >R >R >R >R >R R> DUP . R> DUP . R> DUP . R> DUP . R> DUP . R> DUP . R> DUP . R> DUP . ; \ ???? displays PSWI OUTP IN ANI and DSTACK 8 levels. Enter FFFF, sets lowest one visible as bottom, so 7 left : ??? PSWI @ . OUTP @ . IN @ . ANI @ . base @ >r hex .S r> base ! ; \ Debug 2 - prints 4 variables + Data + Stack differently
0 PWM ! \ not used for now 0 SWI ! \ not used for now 9 PSWI ! \ Set this combined variable to 9 = 1001 this will show the PWM LED ON and T1 ON 0 OUTP ! \ All bits LOW 0000 3 IN ! \ The IN variable set to 3 0011 - prepared to try AND OR XOR INVERT F ANI ! \ Set to F, so all bits HIGH, free for any use, e.g. program an extra counter, or for other tests F HOU ! \ not used for now \ FFFF ALL ! \ ALL will be the combined 16 Bit Vector PWSI OUT IN ANI later , was commented out here for now
: PWH PSWI @ $8 OR PSWI ! MBV2 ; \ Get the variable onto stack, set bit 3 using OR, and store it back, now update the Display : T3H PSWI @ $4 OR PSWI ! MBV2 ; \ Get the variable onto stack, set bit 2, and store it back, see above : T2H PSWI @ $2 OR PSWI ! MBV2 ; \ And the same for setting all of the other bits : T1H PSWI @ $1 OR PSWI ! MBV2 ; : O3H OUTP @ $8 OR OUTP ! MBV2 ; \ x x x x 1 0 0 0 : O2H OUTP @ $4 OR OUTP ! MBV2 ; \ 0 1 0 0 : O1H OUTP @ $2 OR OUTP ! MBV2 ; \ 0 0 1 0 : O0H OUTP @ $1 OR OUTP ! MBV2 ; \ 0 0 0 1 : I3H IN @ $8 OR IN ! MBV2 ; : I2H IN @ $4 OR IN ! MBV2 ; : I1H IN @ $2 OR IN ! MBV2 ; : I0H IN @ $1 OR IN ! MBV2 ; : A3H ANI @ $8 OR ANI ! MBV2 ; : A2H ANI @ $4 OR ANI ! MBV2 ; : A1H ANI @ $2 OR ANI ! MBV2 ; : A0H ANI @ $1 OR ANI ! MBV2 ; \ here end the words that Set Bits HIGH - the next ones set the same bits LOW using AND : PWL PSWI @ $7 AND PSWI ! MBV2 ; \ x x x x 0 1 1 1 : T3L PSWI @ $B AND PSWI ! MBV2 ; \ 1 0 1 1 : T2L PSWI @ $D AND PSWI ! MBV2 ; \ 1 1 0 1 : T1L PSWI @ $E AND PSWI ! MBV2 ; \ 1 1 1 0 : O3L OUTP @ $7 AND OUTP ! MBV2 ; : O2L OUTP @ $B AND OUTP ! MBV2 ; : O1L OUTP @ $D AND OUTP ! MBV2 ; : O0L OUTP @ $E AND OUTP ! MBV2 ; : I3L IN @ $7 AND IN ! MBV2 ; : I2L IN @ $B AND IN ! MBV2 ; : I1L IN @ $D AND IN ! MBV2 ; : I0L IN @ $E AND IN ! MBV2 ; : A3L ANI @ $7 AND ANI ! MBV2 ; : A2L ANI @ $B AND ANI ! MBV2 ; : A1L ANI @ $D AND ANI ! MBV2 ; : A0L ANI @ $E AND ANI ! MBV2 ;
Set I1 and/or I0 of the INPUTs, then call AND01, OR01, XOR01, INVERT0 and see the result of the logic result in OUT0
: AND01 IN @ DUP 1 RSHIFT AND 01 AND OUTP ! MBV2 ; \ Do an AND of IN bit0 and bit1, 00=>1 01=>0 10=>0 11=>1 : OR01 IN @ DUP 1 RSHIFT OR 01 AND OUTP ! MBV2 ; \ Do an OR of IN bit0 and bit1, 00=>0 01=>1 10=>1 11=>1 : XOR01 IN @ DUP 1 RSHIFT XOR 01 AND OUTP ! MBV2 ; \ Do an XOR of IN bit0 and bit1, 00=>0 01=>1 10=>1 11=>0 : INVERT0 IN @ INVERT 01 AND OUTP ! MBV2 ; \ Do an INV of IN bit0, 0=>1 1=>0
\ Forth Words used - remember: Any Forth Word consists of a character sequence plus a space (not allowed in Words is Space ) \ 0 INCLUDE INCLUDE loads and starts a file in VFX; set up c:\VFXTESTAPP, store file there, type INCLUDE c:\VFXTESTAPP\VFXTESTAPP.f \ 1 HEX Mostly VFX recognizes numbers as decimal or HEX. If in DECIMAL mode any Hex Number will give an error. Careful! \ 2 \ \ and a Space after it tells Forth, that the rest of the line is for documentation, so is ignored by VFX. \ 3 : : starts new Forth Word definition, is terminated by ; see Number 6. Example : Bell 07 EMIT ; sends a sound. \ 4 ." ." and a space starts a string of characters to be sent to the screen, the string is terminated by " \ 5 CR CR defines a word that places the cursor to the beginning of the next line \ 6 ; ; ends the definition started by : see number 3 \ 7 TEST TEST is the name of a new word defined just to display the GUI - the Graphical User Interface \ 8 Variable Variables = named memory locations. VARIABLE xx defines, nn xx ! sets, xx @ . prints. Remember: NAME and contents \ 9 DUP DUP takes the value on top of the stack and puts the same value on top as NEW TOS - Top of Stack \ 10 $n $n - the $ ensures that VFX takes the number following as hexadecimal number \ 11 AND AND is a logical operator. works on the two top numbers on the stack, on a bitwise basis, only leaves result \ 12 IF IF is not zero do A - ELSE do B - THEN continue \ 13 ELSE \ 14 THEN \ 15 LSHIFT LSHIFT does a bitwise shift of the value on stack, expects the number of shifts to be done on stack - 1 LSHIFT \ 16 SPACE SPACE sends a space to the screen \ 17 DROP DROP does the opposite to DUP; DROP takes the TOS and deletes what was there, all values move up one position \ 18 DV DV is a word that combines the 4x 4 bits of the variables for the screen, 16 Bit wide. \ 19 @ @ stands for me for AT, for example with Variables - xx puts address of xx onto the stack, xx @ gets the value of it \ 20 ?DO ?DO will start a DO word word LOOP, expects the number of loops on stack. ?DO checks if number on stack is 0. \ 21 LOOP Goes back to ?DO until 0, then continues \ 22 PAGE PAGE clears the screen, takes the cursor to the top left position and prints ok \ 23 BEGIN BEGIN starts a loop of words which ends with UNTIL. UNTIL expects a flag on stack; not 0 then to BEGIN else continue \ 24 1+ 1+ is put on stack, adds one to the number below and replaces it. Same function as 1 + as 2 words. \ 25 ! ! is the opposite function to @, and stores the number on stack at a location on stack, e.g. 55 xx ! at Variable xx \ 26 MS MS stands 1 Millisecond delay in software. Careful which base you are in - 256 and 100 the same Dec / HEX \ 27 KEY? Key? Checks, if a key has been pushed as this generates a flag. BEGIN xxxxxxxx KEY? UNTIL - flag stops the loop \ 28 UNTIL UNTIL end the BEGIN … UNTIL loop, exit if flag true. \ 29 EMIT (07 for Bell ) to get audible output from the PC - ( : ) BELL 07 BEL ( ; )sends the bell signal to the speaker \ 30 .S .S is a non-destructive display of the stack, all of the items there \ 31 . . is similar to .S, prints out the top item only and as well consumes it; an easy way to get rid of the top stack item \ 32 >R >R takes an item from DSTACK and moves to the RSTACK; \ 33 R> R> does the opposite: take item from RSTACK move it to the top of DSTACK \ 34 ( and ) These 2 brackets are used to put explanations within the code, and this is ignored by Forth, similar to \ \ ------ it seems this covers all of the words needed for this little sandbox application
We know this application is not programmed optimally - but this was not the target - beginner's code for beginners. Easy to follow and to explain.
sos \ -- send SOS
counter \ -- start COUNTER 400 SCOUNTER \ start a selectable counter where the number defines the counting speed
Make your own words: NAME example
Add a new word, from
: Name ." Hello Forth World " ;
: NameP ." Hello, my name is XXXX, I am the next president of the United States " ;
Use it interactively, type:
Now use more interactive words. Clear the screen ( Page CR ) , print your word ( Name , wait 1000 ms ( 1000 ms ) , get OK from Forth
Page CR NameP 1000 ms
The Forth Machine
Data stream coming in on the left, THE_STACK, RETURN_STACK, Variables in memory, other memory, route to screen and digital Out. Digital_In and Digital_Out are for later, the same applies to Memory.
The Forth Machine looks very complicated – but people actually use a similar model every day at their desk:
work coming in --> store on stack1 or 2 if needed --> execute --> results out
|(for later)||DS-1||RS-1||x6||(for later)|
|Token_n T7 T6 T5 T4 T3 T2 T1 T0||FFFF(-7)||FFFF||ANI||x0||Hello Forth World|
ExMark October 2016
To get Started
Open the PDF File further down VFXTESTAPP.
- Page 1-3 the VFXTESTAPP - just to look at the code
- Page 4 the Forth Machine – how data is processed internally
- Page 5 the installation information, to get the software to run the application on your PC
- Page 6 the different parts of VFX – open the DFX Debug Console where the VFXTESTAPP will run in Utilities.
The pure text file you have to put into the folder C:\VFXTESTAPP is
VFXTESTAPP as PDF
in portrait format, all on just one page, to print and follow easily.
Some eBooks for further reading at:
And Starting Forth by Leo Brodie for download and print at:
And all of the Forth Words used fit around a Mug.
Binary - Hexadecimal - Decimal Conversion Table
0000 - 0 - 00 0001 - 1 - 01 0011 - 2 - 02 0011 - 3 - 03 0100 - 4 - 04 0101 - 5 - 05 0110 - 6 - 06 0111 - 7 - 07 1000 - 8 - 08 1001 - 9 - 09 1010 - A - 10 1011 - B - 11 1100 - C - 12 1101 - D - 13 1110 - E - 14 1111 - F - 15