Embedded Strings in your Code Space

[Darrel Taylor]

mytekcontrolsm,

Using a Lookup for strings can use up a huge amount of code. And I believe I may have the solution you're looking for.

How to store and retrieve strings in Code Space

Another person that I helped out a while back had his 877 completely maxed out with Lookups for strings to be displayed on an LCD. After converting them to the STRINGS in CODE format, it only took up 1.5K words. Leaving 6.5K for more program. We were both amazed.

And, I too will not be Jumping ship anytime soon. PBP is just to good.

Darrel

[Bruce]

Nice job Darrel, and thanks for the excellent resource. I've used several of
your routines on various projects.

Here's something similar for the 18F series.

DEFINE LOADER_USED 1
DEFINE OSC 4

ptr_pos	VAR BYTE
temp	VAR BYTE
x	VAR BYTE

Main:
   CALL USART_Init
   ptr_pos = 0
   CALL Start
   ptr_pos = 16
   CALL Start
   ptr_pos = 48
   CALL Start
   ptr_pos = 176
   CALL Start

Done:
   GOTO Done
    
ASM
_USART_Init
   movlw   B'00100100'   ;initialize USART
   movwf   TXSTA	 ;8-bit, Async, High Speed
   movlw   .25           ;value for 9600 bps @ 4MHz
   movwf   SPBRG	 ;set SPBRG for 9600 bps @ 4MHz
   movlw   B'10010000'   ;enable USART
   movwf   RCSTA
   return

;----Lookup & send text messages--------------------------
_Start
   movlw   UPPER msg_table
   movwf   TBLPTRU
   movlw   HIGH msg_table
   movwf   TBLPTRH
   movlw   LOW msg_table
   movwf   TBLPTRL
   movf    _ptr_pos,W	;prt_pos must hold message address
   addwf   TBLPTRL,F
   clrf    WREG
   addwfc  TBLPTRH,F
   addwfc  TBLPTRU,F

Next_Char
   tblrd   *+
   movff   TABLAT,_temp
   bra     Test_EOM      ;test for EOM character
	
Continue
   movf	  _temp,W	 ;move temp to w
   movwf  TXREG		 ;send it
   btfss  TXSTA,TRMT	 ;wait for data TX
   goto   $-2
   bra	  Next_Char      ;fetch next message character from table
	
Test_EOM
   movlw  "~"            ;check for EOM character
   cpfseq  _temp, 1	 ;compare temp with w, if temp = ~ then end			
   bra     Continue      ;no EOM, so continue
   movlw   "\r"		 ;move data into TXREG
   movwf   TXREG	 ;send carriage return
   btfss   TXSTA,TRMT	 ;wait for data TX
   goto    $-2	
   movlw   "\n"		 ;move data into TXREG
   movwf   TXREG	 ;send line feed
   btfss   TXSTA,TRMT	 ;wait for data TX
   goto    $-2
   return                ;finished with message, return to caller
ENDASM

ASM
msg_table	; Message strings
   data	" Message #1~    ";Message #1 starts at msg_table 0
   data	" Message #2~    ";Message #2 starts at msg_table 16, etc,
   data	" Message #3~    ";32
   data	" Message #5~    ";48
   data	" Message #6~    ";64
   data	" Message #7~    ";80
   data	" Message #8~    ";96
   data	" Message #9~    ";112
   data	" Message #10~   ";128
   data	" Message #11~   ";144
   data	" Message #12~   ";160
   data	" Message #13~   ";176
ENDASM

[Darrel Taylor]

Now there's an endorsement I can be proud of.

Thanks Bruce!

[mytekcontrols]

Thanks Darrel and Bruce for your great examples. I would have to say I like Darrel's approach the best, since it seems less cryptic as to what the messages are (i.e; you can give them meaningfull names). Also I like the idea that they can be located anywhere in the program (kinda like my 6502 example). However I am using an 18F252 for my project, and apparently this approach wont work with a 16 bit processor. Any ideas how this could be changed?

[Bruce]

' Text message addresses w/specific names
Intro CON 0
PumpOn CON 16
PumpOFF CON 32 ' etc,,

   ptr_pos = Intro     ' print intro message
   CALL Start
   ptr_pos = PumpON ' print pump on message, etc,,,
   CALL Start

You now have meaningful names for your strings. It's not that cryptic once
you've played with it a bit. The 18F series are easier to code in .asm than
16F parts.

Make your strings as long as you like. That was just a quick/simple example.

I don't have an example for placing strings all over code space since I would
never do that. PBP library functions & my app code get first pick. Huge
chunks of text messages get the left-overs at the bottom...;o]

[Darrel Taylor]

Hi again Michael,

I guess it was about time anyhow. Haven't updated it since 2003.

I've modified the Strings program to be able to work with 16-bit devices.

Between Bruce's example and the new one, I'm sure you'll get what you need.

It's still in the same place ... How to store and retrieve strings in Code Space

Best regards,
   Darrel

[mytekcontrols]

Hi Bruce,

I have been studying your code that you posted here on doing message tables from assembly code, and quite frankly I am baffled by parts of it. This wouldn't be problem if I could use it as is, but I really need to have the pointer increments to be by 1 (i.e.; 0,1,2,3,4,5,6, ect.).

Here are some snippits of your code with some questions I have next to them. If you get a chance can you please explain what is going on?

; This section appears to be locating the message table, but Im not
; really sure specifically what is going on especially with the first part
; where you are moving Upper msg_table into TBLPTRU
; (what is UPPER? I've used HIGH and LOW before, but never UPPER).
; TBLPTR is obviously short for Table Pointer.

   movlw   UPPER msg_table 
   movwf   TBLPTRU
   movlw   HIGH msg_table
   movwf   TBLPTRH
   movlw   LOW msg_table
   movwf   TBLPTRL

; Now here we seem to be adding an offset into the message table using
; the same pointers we previously set to what I am asuming is the base
; address of our message table. This is where the beginning of a particular
; message resides within the table (correct?). Now here comes the questions
; of particular interest to me; does the fact that your pointers are in 16 byte
; increments mean that each message string can only be up to 16 bytes long?
; Or can the pointer be changed to any increment desired?

  movf    _ptr_pos,W	;prt_pos must hold message address
   addwf   TBLPTRL,F
   clrf    WREG
   addwfc  TBLPTRH,F
   addwfc  TBLPTRU,F

; Ok now that we have our index to a message set, we can begin retrieving
; the characters one by one, until we see the EOM character "~". What is
; tblrd   *+ or more specifically *+ (is this doing a read and then increment?)
; Oh and what is "goto   $-2" doing? (specifically $-2).

Next_Char
   tblrd   *+
   movff   TABLAT,_temp
   bra     Test_EOM      ;test for EOM character
	
Continue
   movf	  _temp,W	 ;move temp to w
   movwf  TXREG		 ;send it
   btfss  TXSTA,TRMT	 ;wait for data TX
   goto   $-2
   bra	  Next_Char      ;fetch next message character from table
	
; This part is fairly obvious, although there are some more of those $-2
; which I don't understand the purpose of, and what does "\r"
; and "\n" do? Actually to be more specific since I can see your comments,
; what my question really is; what or how does moving a literal of "\r" into
; W actually move the data (which I assume is a character from the table).

Test_EOM
   movlw  "~"            ;check for EOM character
   cpfseq  _temp, 1	 ;compare temp with w, if temp = ~ then end			
   bra     Continue      ;no EOM, so continue
   movlw   "\r"		 ;move data into TXREG
   movwf   TXREG	 ;send carriage return
   btfss   TXSTA,TRMT	 ;wait for data TX
   goto    $-2	
   movlw   "\n"		 ;move data into TXREG
   movwf   TXREG	 ;send line feed
   btfss   TXSTA,TRMT	 ;wait for data TX
   goto    $-2
   return                ;finished with message, return to caller

If I was better versed in the assembly aspects of the 18F series I could probably figure this out on my own, but I only recently began working with this series of PIC chips.

Any help you can offer is appreciatted.
Thanks,

[Bruce]

Hi Michael,

Download the PICmicro® 18C MCU Family Reference Manual... or just the chapters you need from here;

http://www.microchip.com/stellent/id...GE&nodeId=2054

There's a whole section on table read/write with detailed explanations that should answer every question you have.

Much easier than me re-typing it all. If you have questions after reading section 8 let me know.