Post by thread:[PIC]: Pseudo-Random numbers

Hello all. I need to generate numbers that appear to be ranomized, it makes no difference if they are truly random. I can seed it with a value culled from ram before i wipe the ram, but it's not necessary. Any simple code to generate a seemingly random number, from 0 to 255? -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

At 11:36 PM 8/18/01 -0400, Ron Anthony wrote: >Hello all. I need to generate numbers that appear to be ranomized, it makes >no difference if they are truly random. I can seed it with a value culled >from ram before i wipe the ram, but it's not necessary. > >Any simple code to generate a seemingly random number, from 0 to 255? I have a 19 bit PN generator implementation in AVR code on my web site. It's in the "getting started" firmware, under microcontrollers. You shouldn't have any trouble porting it over to picish. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

Dave, any 8 bit prefab for PIC? call me lazy... -----Original Message----- From: pic microcontroller discussion list [PICLISTKILLspamMITVMA.MIT.EDU]On Behalf Of David VanHorn Sent: Sunday, August 19, 2001 12:34 AM To: .....PICLISTKILLspam.....MITVMA.MIT.EDU Subject: Re: [PIC]: Pseudo-Random numbers At 11:36 PM 8/18/01 -0400, Ron Anthony wrote: >Hello all. I need to generate numbers that appear to be ranomized, it makes >no difference if they are truly random. I can seed it with a value culled >from ram before i wipe the ram, but it's not necessary. > >Any simple code to generate a seemingly random number, from 0 to 255? I have a 19 bit PN generator implementation in AVR code on my web site. It's in the "getting started" firmware, under microcontrollers. You shouldn't have any trouble porting it over to picish. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

----- Original Message ----- From: Ron Anthony <@spam@ronantKILLspamOPTONLINE.NET> > Dave, any 8 bit prefab for PIC? call me lazy... A better thing to do would be to search the PIClist site. There is a lot of good stuff there and code or algorithms to solve most common problems. It saved me a post or two looking there _before_ asking a question. Jeff -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

> Any simple code to generate a seemingly random number, from 0 to 255? See HAL_RAND.ASPIC at http://www.embedinc.com/pic/hal.htm. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, RemoveMEolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestspamBeGonemitvma.mit.edu

At 04:17 AM 8/19/01 -0400, Ron Anthony wrote: >Dave, any 8 bit prefab for PIC? call me lazy... Nope, sorry. The closest would be a 7 bit version, and I don't have any pic code on my site. You can find the method in the later ARRL handbooks, under specialized communications. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

From piclist.com: www.piclist.com/techref/microchip/rand8bit.htm I used: LFSR: RLF RANDOM,W RLF RANDOM,W BTFSC RANDOM,4 XORLW 1 BTFSC RANDOM,5 XORLW 1 BTFSC RANDOM,3 XORLW 1 MOVWF RANDOM RETLW 0 (Andrew Warren) For extra confusion, TMR0 ran in the background with no prescaller. Every time TMR0 interupted, I ran the above code and loaded RANDOM into TMR0. When ever I needed a Random number, I load the value from TMR0. You don't need to use TMR0 or interupt, it was free in this application so I used it. Quentin -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

The following code implements a linear feedback register type of pseudo-random number generator. This algorithm is frequently implemented in hardware for spread-spectrum radio applications. It will generate all possible bit combinations EXCEPT all zeroes, for various lengths, if the value is Poly is chosen correctly, and Variable is initialized with any non-zero number. In other words, it will produce a "maximal length sequence", in which each of 2^n-1 nonzero bit combinations appear once and only once. If Variable is initialized with 0, then it just produces lots of zeroes. This macro was used in an application where a pseudo-random stream of bits was needed, hence its output of a bit in CY. If you want up to an 8-bit value, it will be contained in Variable after executing the macro. Suitable values for Poly: for 6 bits (sequence length 63): 0x21, 0x33, 0x36 for 7 bits (sequence length 127): 0x41, 0x44... for 8 bits (sequence length 255): 0x8e, 0xb4... For more suitable Poly values see: Dixon, Robert C., Spread Spectrum Systems with Commercial Applications; (Table 3.7) ;------------------------------------------------------------ ; GenerateLRC Macro -- generates up to 8-bit LRC ; ; Input: Variable -- needs to be initialized (usually all ones to # of bits) ; ; Output: Next output bit is in CY, Variable is updated for next cycle ; ;------------------------------------------------------------ GenerateLRC Macro Poly, Variable clrc rlf Variable,f movlw Poly skpnc xorwf Variable,f endm > {Original Message removed}

At 08:26 AM 8/20/01 -0500, Don Hyde wrote: >The following code implements a linear feedback register type of >pseudo-random number generator. This algorithm is frequently implemented in >hardware for spread-spectrum radio applications. > >It will generate all possible bit combinations EXCEPT all zeroes, for >various lengths, if the value is Poly is chosen correctly, and Variable is >initialized with any non-zero number. You're right, but as long as you use less than the full length of the shift register, you can get all states. In one app, I use 8 bits from the 19 bit version, picked more or less at random, with some bit inversions and anding. But the initial byte that I grab can have any state. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads