Post by thread:Store data in rom (f877)

Hello everyone Got a big program here hope you can help me I try to store text msg using retlw but they can exceed 256 bytes it will cause stack overflow causing the whole program to restart if the whole program is within 256 then everything is ok and perfect is something to do with the retlw Is there any other way of storing text msg in 16f877 can any one help me on this thanks regards soon lee

Soon Lee wrote: > Is there any other way of storing text msg in 16f877 > can any one help me on this You can store the string via "da" directive and read it out directly. An example: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - MY_STRING da "Hello World!", 0 [..] LCD_BUFFER equ 0x54 [..] SWITCHBANK_0_2 movlw (MY_STRING & 0xff) ; store Lo Byte movwf EEADR movlw (MY_STRING >> 8) ; store Hi Byte movwf EEADRH SWITCHBANK_2_0 [..] LCD_PrintText LCD_PrintTextLoop SWITCHBANK_0_3 bsf EECON1, EEPGD ; point to program memory bsf EECON1, RD ; EEPROM Read nop nop SWITCHBANK_3_2 incf EEADR, F ; increment memory pointer skpnz incf EEADRH, F rlf EEDATA, W ; shift in bit7 of low byte rlf EEDATH, W SWITCHBANK_2_0 movwf LCD_BUFFER ; only for testing tstf LCD_BUFFER bz LCD_PrintTextEnd call LCD_SendChar ; print out first char SWITCHBANK_0_2 movf EEDATA, W ; load low byte andlw 0x7f SWITCHBANK_2_0 bz LCD_PrintTextEnd call LCD_SendChar ; print out second char goto LCD_PrintTextLoop LCD_PrintTextEnd return -- _____________________________________________ _/ uC-Stuff for MIDI at http://go.to/uCApps /_______ / Music is aesthetisized frequency (Klaus Schulze) / ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Hi Pearce Retlw only can be used within 256 byte of mermory, if the return address crosses the 256 block it will cause stack overflow, i have try on the mplab. as long as the return address and the retlw is in the same 256 block it is ok but else ..... regards soon lee ----- Original Message ----- From: Alan B Pearce <spam_OUTA.B.PearceTakeThisOuTRL.AC.UK> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Sunday, April 16, 2000 7:52 PM Subject: Re: Store data in rom (f877) > Store the string in EEPROM which will allow you save code space, and when this > overflows put the rest in RETLW instructions. > > Otherwise use an external EEPROM.

>Retlw only can be used within 256 byte of mermory, if the return address >crosses the 256 block it will cause stack overflow, i have try on the mplab. >as long as the return address and the retlw is in the same 256 block it is >ok but else ..... It was while I was writing the piece that I realised the new 16F877 is limited to 256 bytes EEPROM as well, which is why I suggested using the EEPROM for most of the table, then when you get an overflow incrementing the EEPROM address counter, go on to use RETLW method. This would be alright for up to 512 bytes of data. There have been methods published in the list and I think there is aa AN note from microchip on how to cross page boundaries when using RETLW tables. Look in the Piclist FAQ. If you do not mind adding a chip and having the data stored outside the pic chip, then an I2C interface is probably the easiest.

Alan B Pearce wrote: > It was while I was writing the piece that I realised the new 16F877 is limited > to 256 bytes EEPROM as well, which is why I suggested using the EEPROM for most > of the table, then when you get an overflow incrementing the EEPROM address > counter, go on to use RETLW method. This would be alright for up to 512 bytes of > data. Why are you using the data EEPROM on 16F877? Just take the program memory, you can read it out like the data EEPROM and there is enough space for up to 16000 7-Bit characters... see my example above. Best Regards, Thorsten. -- _____________________________________________ _/ uC-Stuff for MIDI at http://go.to/uCApps /_______ / Music is aesthetisized frequency (Klaus Schulze) / ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It's not impossible to use a table or retlw's that's larger than 256 locations, just a little more trouble since you need to use and compute a double-precision pointer. ; GetByteFromBigTable -- fetches a byte from a table larger than 256 locations ; pointerlow and pointerhigh are the double-precision pointer into the table. ; NOTE -- PCLATH is altered, so you will need to restore it before executing ; any goto or call instructions! GetByteFromBigTable: movlw low BigTable ;start adding pointer to address of table addwf pointerlow,w movwf temp ;low half of double-precision add movlw high BigTable ;now start the high half movwf PCLATH skpnc incf PCLATH,f ;propagate the carry, if any from low half movfw pointerhigh addwf PCLATH,f movfw temp movwf PCL ;jump into the table BigTable: retlw 'a' retlw 'b' etc. Note that BigTable does not need to be in the same page with GetByteFromBigTable, and does not need to either start or end on a page boundary. > {Original Message removed}

Soon Lee wrote: > 16000 characters? > 0x3fff=14 bits > the upper byte is truncated to 0x3F > how you store the first 7 then the next seven? > using what code. > please enlighten me Simply use the "da" directive of MPASM (see help page) See my example in <38F99D21.74F98D83KILLspamgmx.de> how to handle it. Best Regards, Thorsten. -- _____________________________________________ _/ uC-Stuff for MIDI at http://go.to/uCApps /_______ / Music is aesthetisized frequency (Klaus Schulze) / ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~