Post by thread:Accessing text strings.

I have a program that I am running on a 16c74, this read data from the A/D and converts it to ASCII and sends it down the serial port to a PC. This all works, I've got the A/D and serial stuff all sorted.. What I want to do is to send a text message when the program starts, just a short message such as "Mikes logging program Version 1.00" At the moment I can do this by moving each character into W and then calling my serial routine which sends it down the serial port to the PC MOVLW H'4D' ; move code for ASCII M into W CALL SERIAL_SEND ; sends W to serial and so on for each character.......... I feel there must some way of doing using the DW statement. dw "Mike logging program Version 1.00\n" This puts the text into memory, but how do I then access it? I sure this is one of those things that are really easy when you know how.....:) Thanks Mike Barrett ============================================= Mike Barrett E-mail: spam_OUTbarrettTakeThisOuTcambridge.scr.slb.com Schlumberger Cambridge Research Phone: 01223 325200 High Cross, Cambridge, CB3 OEL. U.K Fax: 01223 327019 =============================================

> Yes, strings are a pain on the PIC. You could also get fancy and have > predefined constant offsets into a string table, i.e. > > StrTable > retw "String1",0 > retw "Long String",0 > retw "3rd string",0 There are some other tricks that can be handy for such things, e.g. if there were an "addwf PC" at StrTable above, you could use something like: DumpStringN: movwf N ; Procedure to dump Nth string in above table [1=1st] clrf Index DumpLoop: movf Index,w incf Index,f call StrTable iorlw 0 ; Check if W is zero btfss Z goto FindLoop decfsz N goto FindLoop DumpLoop: movf Index,w incf Index,f call StrTable iorlw 0 ; Check if W is zero btfsc Z retlw 0 call PrintChar goto DumpLoop A bit of a hack, but I've found similar techniques to be sometimes useful with the CCS compiler which does not include any really good methods for doing the above. BTW, another useful trick when writing code that should be equivalent to printf("Answer=%3d Result=%05D", answer, result); is to code it like this [more or less]; note that if there weren't very many printfs, it might be better to put more of the work in the "format" section and less in the library section. Note that "Format" is designed to be used as a string in a string-print procedure. Format: db "Answer=" movlw answer call IntPConvert goto BGetHund goto BGetTens goto GetOnes db " Result=" call IntPConvert goto GetTenK goto GenThou goto GetHund goto GetTens goto GetOnes retlw 0 IntPConvert: bsf blankflag movwf FSR movf IND,w movwf TempL incf IND movf IND,w movwf TempH goto Convert ; My wonderful bin->dec convert routine BGetThou: movf Thou,w goto GetWBlank BGetHund: movf Hund,w goto GetWBlank BGetTens: movf Tens,w GetWBlank: btfss Z bcf BlankFlag btfsc BlankFlag movlw $F0 addlw 48 return GetTenK: movf TenK,w goto GetDigit GetThou: movf Thou,w goto GetDigit GetHund: movf Hund,w goto GetDigit GetTens: movf Tens,w goto GetDigit GetOnes: movf Ones,w GetDigit: addlw 48 return

-----Original Message----- From: John Payson <.....supercatKILLspam@spam@MCS.NET> To: PICLISTKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Date: Friday, February 06, 1998 6:31 PM Subject: Re: Accessing text strings. {Quote hidden}>> Yes, strings are a pain on the PIC. You could also get fancy and have >> predefined constant offsets into a string table, i.e. >> >> StrTable >> retw "String1",0 >> retw "Long String",0 >> retw "3rd string",0 > >There are some other tricks that can be handy for such things, e.g. if >there were an "addwf PC" at StrTable above, you could use something >like: > Ok... I've been watching this thread for a while and have a very basic observation: what is the mnemonic retw supposed to imply? I don't recognize it. In my thinking you would have to use the directive dt to achieve the jump table John is indicating. >Format: > db "Answer=" > movlw answer > call IntPConvert > goto BGetHund > goto BGetTens > goto GetOnes > db " Result=" > call IntPConvert Also: what purpose does db serve in this instance? (1) In garden variety PICs there is no way to access program memory directly, so without the retlw prefix, this db data appears useless. (2) The db and dw directives 'pack' the data into program memory as if it were a sequence of 8 bit bytes. The net result in, for example, a 14 bit architecture is that the two high-order bits of every other byte is discarded. See a code snippet following, along with the resultant MPASM 2.01 listing. Brian +++begin of code snippet LIST p=16f84 org 0xff db "abc" dw "abc" dt "abc",0 retlw 0 ;(this line demonstrates that dt 0 does indeed generate the retlw machine language. look at the listing) END +++end of code snippet +++begin of MPASM 2.01 output due to code snippet 00001 00002 LIST p=16f84 00FF 00003 org 0xff 00004 Message[303]: Program word too large. Truncated to core size. (6162) Message[303]: Program word too large. Truncated to core size. (6300) 00FF 2162 2300 00005 db "abc" ;this packs data byte Message[303]: Program word too large. Truncated to core size. (6162) Message[303]: Program word too large. Truncated to core size. (6300) 0101 2162 2300 00006 dw "abc" 0103 3461 3462 3463 00007 dt "abc",0 3400 0107 3400 00008 retlw 0 00009 END

Hi! 6-Feb-98 17:21 John Payson wrote about "Re: Accessing text strings.": >> > Yes, strings are a pain on the PIC. :( >> BTW, another useful trick when writing code that should be equivalent to >> printf("Answer=%3d Result=%05D", answer, result); >> is to code it like this [more or less]; note that if there weren't very >> many printfs, it might be better to put more of the work in the "format" >> section and less in the library section. Note that "Format" is designed >> to be used as a string in a string-print procedure. >> >> Format: >> db "Answer=" >> movlw answer >> call IntPConvert >> goto BGetHund >> goto BGetTens >> goto GetOnes >> db " Result=" ..... >> IntPConvert: >> bsf blankflag >> movwf FSR >> movf IND,w >> movwf TempL >> incf IND >> movf IND,w >> movwf TempH >> goto Convert ; My wonderful bin->dec convert routine ..... Unfortunatly, one should note that this code can't be used exactly as a string. The string planned to be read is: 0123456789 (index in "CALL ReadFormat") "Answer=ddd".. (string to be read; ddd is the decimal value of the two bytes pointed by answer) Actually, we shell read "Answer=", but then some strange effects will be produced. (I suppouse that "Convert" makes convertion only). If index==7 then instructions "movlw answer" and "call IntPConvert" will be done. So, the value returned by conversion rotine "Convert" will be obtained by caller instead of the first digit of ansver (hundreds). If index==8 then only "call IntPConvert" will be done, and W will cotain value of 8 (if "addwf PCL,f" is used). So, TempL and TempH will be replaced with the values of SFR's 0x08 and 0x09 "Convert" routine will be called again. The value returned by "Convert" will be included into the string too. The string will be like this: 0123456789012 (index in CALL ReadFormat) "Answer=??ddd".. (string; '?' is unpredictable chars returned by "Convert") To avoid this one should perform additional increment by 2 the value of "index" in routine "Convert" or in code labeled with "IntPConvert" (it is better, because routine "Convert" remain unchanged and can be called with no connection with any strings). But generally, nobody can know what variable was used as index in "CALL ReadFormat". Thus we have to use the same variable ("format_index") for every format string. Another method is to make some improvements. Every char of the desired string should be represented by the only command. It may be something like this: Format: db "Answer=" ; movlw answer ; call IntPConvert ; goto BGetHund goto GetAnswer_And_Hund ;; !!! goto BGetTens goto GetOnes db " Result=" ..... GetAnswer_And_Hund: movlw answer call IntPConvert goto BGetHund IntPConvert: bsf blankflag movwf FSR movf IND,w movwf TempL incf IND movf IND,w movwf TempH goto Convert ; My wonderful bin->dec convert routine ..... Now if index==7 then "goto GetAnswer_And_Hund" will be executed. The desired value vill be transfered into TempL,TempH; "Convert" will be called and executed but returned value ignored; then "goto BGetHund" will be executed and the digit of hundreds of the desired number will be returned as a next char of the string. The next call (index==8) will cause the "goto BGetTens" executed and so on. I use method like described above for an interfacing to formatted output library. But I don't build a "string-like" code. Instead of this I build an "output list". Here is a siplified example (FMT... are entry points of library routines; index of current processing element is mantained in the library): Example: goto FMT_BLANK goto proc_answer_string goto proc_asnwer_value goto FMT_BLANK ; there are special entries for often used chars goto FMT_COMMA ; like " .,;:+-*" goto FMT_ENDLIST ; No comments :) proc_answer_value: movlw answer goto FMT_03D_I ; Use "%03d" coversion, "FMT..._I" means ; indirect addressing proc_answer_string: movlw high(answer_string) movwf hi_addr movlw low(answer_string) goto FMT_S_ROM answer_string: db "Answer=",0 This example was mentioned as simplified because this library has many other entry points. For example it is not efficient to use FMT_03D_I in this case. There is another entry (let us refer it as FMT_03D_I_ALT). It produce the same effect as FMT_03D_I but index of current processing element will be incremented by 2. So, we can eliminate one GoTo command and one label. (It's not joke, total number of labels will be too high and the risk of undetected mistypes will be very high too.) The example became as follows: printf(" Answer=%03d, ", *answer); Example: goto FMT_BLANK goto proc_answer_string movlw answer goto FMT_03D_I_ALT goto proc_asnwer_value goto FMT_COMMA ; there are special entries for often used chars goto FMT_BLANK ; like " .,;:+-*". It was not necessary to use ; this possibility here. It's illustration only goto FMT_ENDLIST ; No comments :) proc_answer_string: movlw high(answer_string) movwf hi_addr movlw low(answer_string) goto FMT_S_ROM answer_string: db "Answer=",0 Entry point FMT_S_ROM (and other string rotines) maintain its own internal index (rather than index of the list elements) for access to procesing string. This library can be used to implement more complicated printfs. For example: printf("Status is \'%s\'", ok==0?"Failed":"OK!"); Actually will be implemented some other printf: printf("%s%s%c", "Status is \'", ok==0?"Failed":"OK!",'\''); Example2: goto proc_status_string goto proc_status_report movlw "'" goto FMT_C_ALT

Hi! 12-Feb-98 06:23 PICLISTspam_OUTMITVMA.MIT.EDU wrote about "Re: Accessing text strings.": >> Hi! >> 6-Feb-98 17:21 John Payson wrote about "Re: Accessing text strings.": >> >> >> >> >> Format: >> >> db "Answer=" >> >> movlw answer >> >> call IntPConvert >> >> goto BGetHund >> >> goto BGetTens >> >> goto GetOnes >> >> db " Result=" >> ..... >> >> IntPConvert: >> >> bsf blankflag >> >> movwf FSR >> >> movf IND,w >> >> movwf TempL >> >> incf IND ^^^^ mistype? "FSR", I think... >> >> movf IND,w >> >> movwf TempH >> >> goto Convert ; My wonderful bin->dec convert routine >> ..... ..... >> Actually, we shall read "Answer=", but then some strange effects >> will be produced. (I suppouse that "Convert" makes conversion only). >> >> If index==7 then instructions "movlw answer" and >> "call IntPConvert" will be done. So, the value returned by >> conversion rotine "Convert" will be obtained by caller instead >> of the first digit of ansver (hundreds). >> >> If index==8 then only "call IntPConvert" will be done, and W >> will cotain value of 8 (if "addwf PCL,f" is used). So, TempL and >> TempH will be replaced with the values of SFR's 0x08 and 0x09 >> "Convert" routine will be called again. The value returned by >> "Convert" will be included into the string too. I'm sorry, my explanation wasn't exact. :( It is necessary to replace "CALL IntPConvert" with "GOTO IntPConvert" in quoted program to make this explanation true. But the key problem was noted correctly. Instruction follow "movlw answer" will be executed twice: when index=7 (OK, we want to do this) and when index=8 (unexpected). It is illegal, because no "movlw answer" executed before it; so, routine "Convert" will get "garbage value" in W. Furthermore, it should not be executed at all. -- Vladimir M. Klochko