Post by thread:[PIC:] Baud Rate Generator

Looking at the datasheet for the PIC16F62x (page 73), it lists the async serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value (0 to 255), with BRGH=1. It APPEARS I should be able to make X=0 with Fosc=4MHz and get 250 kbps. However, if we look on page 75 of the datasheet, it lists 250kbps as NA with Fosc=4MHz. Which is correct? Thanks! Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

Harold M Hallikainen wrote: > Looking at the datasheet for the PIC16F62x (page 73), it lists the async >serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value (0 to >255), with BRGH=1. It APPEARS I should be able to make X=0 with Fosc=4MHz >and get 250 kbps. However, if we look on page 75 of the datasheet, it >lists 250kbps as NA with Fosc=4MHz. > Which is correct? > 4 MHz /16 /2 = ??? X must be 1 or more! {Quote hidden}> >Thanks! > >Harold > > >FCC Rules Online at http://hallikainen.com/FccRules >Lighting control for theatre and television at http://www.dovesystems.com > >________________________________________________________________ >GET INTERNET ACCESS FROM JUNO! >Juno offers FREE or PREMIUM Internet access for less! >Join Juno today! For your FREE software, visit: >dl.http://www.juno.com/get/web/. > >-- >http://www.piclist.com hint: To leave the PICList >.....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu > > > -- * | __O Thomas C. Sefranek tcsKILLspamcmcorp.com |_-\<,_ Amateur Radio Operator: WA1RHP (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz ARRL Instructor, Technical Specialist, VE Contact. hamradio.cmcorp.com/inventory/Inventory.html http://www.harvardrepeater.org -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

On Wed, 16 Jan 2002 15:18:10 -0500 "Thomas C. Sefranek" <EraseMEtcsspam_OUTTakeThisOuTCMCORP.COM> writes: > Harold M Hallikainen wrote: > > > Looking at the datasheet for the PIC16F62x (page 73), it > lists the async > >serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value > (0 to > >255), with BRGH=1. It APPEARS I should be able to make X=0 with > Fosc=4MHz > >and get 250 kbps. However, if we look on page 75 of the datasheet, > it > >lists 250kbps as NA with Fosc=4MHz. > > Which is correct? > > > 4 MHz /16 /2 = ??? X must be 1 or more! > Page 73 of the datasheet says "0 to 255". Also, page 75 shows an SPBRG value of 0 giving a bit rate of 223.721 kbps with an oscillator frequency of 3.579 MHz (BRGH = 1). So, does X have to be 1 or more? Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

At 09:48 AM 16/01/2002 -0800, you wrote: > Looking at the datasheet for the PIC16F62x (page 73), it lists > the async >serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value (0 to >255), with BRGH=1. It APPEARS I should be able to make X=0 with Fosc=4MHz >and get 250 kbps. However, if we look on page 75 of the datasheet, it >lists 250kbps as NA with Fosc=4MHz. > Which is correct? I assume that this is for DMX ? I put 20MHz 16F628's in my dimmer project as I came to the conclusion that you need at least a 10MHz clock to do the 250Kbps data rate. I have not written the DMX code for it yet though. SPBRG needs to be 4 at 20MHz and 20MHz/4MHz = 5 so you'd have to have 0.8 for 4MHz ! Maybe a value of 1 at 5MHz would work. (but not for a 4MHz part) The 16F628-20/P is currently cheaper than the 16F628-04/P I've found. Regards... -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu

On Thu, 17 Jan 2002 09:29:19 +1000 David Duffy <KILLspampiclistKILLspamAUDIOVISUALDEVICES.COM.AU> writes: > I assume that this is for DMX ? I put 20MHz 16F628's in my dimmer > project > as I came to the conclusion that you need at least a 10MHz clock to > do the > 250Kbps data rate. I have not written the DMX code for it yet > though. SPBRG > needs to be 4 at 20MHz and 20MHz/4MHz = 5 so you'd have to have 0.8 > for > 4MHz ! Maybe a value of 1 at 5MHz would work. (but not for a 4MHz > part) > The 16F628-20/P is currently cheaper than the 16F628-04/P I've > found. Yes, it's DMX (actually, it's our DMX talk back). I've done bunches of DMX stuff using a PIC at 16 MHz. However, here, I thought I'd use 4 MHz since I should then be able to use any 16F627. The datasheets (for example, page 73 of the PIC16F62X datasheet) say the bit rate is Fosc/(16(X+1)) if BRGH=1. Solving for X, we get X=(Fosc/(16*BR))-1 . If Fosc=20MHz and BR=250e3, we get X=44 (not 5). Dropping to 4 MHz, we get X=0. So, it seems that it would work. Some have said X has to be between 1 and 255 inclusive, but the datasheet says 0 and 255 inclusive. The datasheet also shows several examples where X=0 (for example, 625 kpbs with Fosc=10 MHz). So, the question remains, why does the datasheet show NA for 250 kbps at 4 MHz? I have since changed my resonator to 16 MHz and found other bugs in the code. I imagine that if I change back to 4 MHz (now that the bugs are removed), it will work... but I don't know if I want to make the effort. Just trying to figure out why the datasheet says 250 kbps at 4 MHz is "NA." Looks like it should work... Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

The tables (at least two of them, but not all) are wrong. The calculation is correct. This has been a problem since they released the data sheets for the 'f87x parts, perhaps even earlier chips with UARTs. Don't trust the tables. -Adam Harold M Hallikainen wrote: {Quote hidden}> Looking at the datasheet for the PIC16F62x (page 73), it lists the async >serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value (0 to >255), with BRGH=1. It APPEARS I should be able to make X=0 with Fosc=4MHz >and get 250 kbps. However, if we look on page 75 of the datasheet, it >lists 250kbps as NA with Fosc=4MHz. > Which is correct? > >Thanks! > >Harold > > >FCC Rules Online at http://hallikainen.com/FccRules >Lighting control for theatre and television at http://www.dovesystems.com > >________________________________________________________________ >GET INTERNET ACCESS FROM JUNO! >Juno offers FREE or PREMIUM Internet access for less! >Join Juno today! For your FREE software, visit: >dl.http://www.juno.com/get/web/. > >-- >http://www.piclist.com hint: To leave the PICList >spamBeGonepiclist-unsubscribe-requestspamBeGonemitvma.mit.edu > > > > > -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

On Wed, 16 Jan 2002 16:21:53 -0800, Harold M Hallikainen wrote: <snip> {Quote hidden}> The datasheets (for example, page 73 of the PIC16F62X datasheet) say the >bit rate is Fosc/(16(X+1)) if BRGH=1. Solving for X, we get >X=(Fosc/(16*BR))-1 . If Fosc=20MHz and BR=250e3, we get X=44 (not 5). >Dropping to 4 MHz, we get X=0. > So, it seems that it would work. Some have said X has to be between 1 >and 255 inclusive, but the datasheet says 0 and 255 inclusive. The >datasheet also shows several examples where X=0 (for example, 625 kpbs >with Fosc=10 MHz). > So, the question remains, why does the datasheet show NA for 250 kbps at >4 MHz? > I have since changed my resonator to 16 MHz and found other bugs in the >code. I imagine that if I change back to 4 MHz (now that the bugs are >removed), it will work... but I don't know if I want to make the effort. >Just trying to figure out why the datasheet says 250 kbps at 4 MHz is >"NA." Looks like it should work... Well, the math sure works. It probably will work as you expect. My presumption is that Microchip doesn't want to commit that all PICs will reliably work at 4 MHz with a zero divider over all temps and Vdd levels. They may have characterized the circuit and found that, while it works reliably up to 3.579 MHz with a zero divider (which they show), it may get flakey above that. At nominal temps and Vdd levels, I wouldn't think that it would be a problem to push it to 4 MHz. (Note: I wouldn't do this in a commercial product. YMMV) Regards, Bob -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

On Wed, Jan 16, 2002 at 09:02:36PM -0500, M. Adam Davis wrote: > The tables (at least two of them, but not all) are wrong. The > calculation is correct. > > This has been a problem since they released the data sheets for the > 'f87x parts, perhaps even earlier chips with UARTs. > > Don't trust the tables. I never have. For all things relating to the PIC USART I use Fr. Thomas McGahee's highly annotated code the describes the operation of the USART, including the formula for bit rate generation. It's an invaluable resource for dealing with the USART and includes many 'gotchas' that have been learned from hard experience. Check it out here: http://mcgahee.freeservers.com BAJ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Thu, 17 Jan 2002, Byron A Jeff wrote: > > Don't trust the tables. > > I never have. For all things relating to the PIC USART I use Fr. Thomas > McGahee's highly annotated code the describes the operation of the USART, > including the formula for bit rate generation. It's an invaluable resource > for dealing with the USART and includes many 'gotchas' that have been learned > from hard experience. Check it out here: > > http://mcgahee.freeservers.com > Agree. However I don't found any diferences between standard formulas: spbrg = (xtal[hz]/(baudrate[bps]*64))-1 for brgh=low spbrg = (xtal[hz]/(baudrate[bps]*16))-1 for brgh=high and rounded formulas: spbrg_value = (((d'10'*XTAL_FREQ/(d'16'*baudrate))+d'5')/d'10')-1 spbrg_value = (((d'10'*XTAL_FREQ/(d'64'*baudrate))+d'5')/d'10')-1 the result is +/- 1 diference in spbrg value which means almost nothing, my test shows that at many baud rates even with +/- 3 from computed spbrg values does not affect asynchronous communications ( not applicable with small spbrgh ) Of course the computed error must be smallest as possible. So my question: do you found any situation when rounded formulas must be applied ? regards, Vasile -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I include the following lines in all my stuff with uarts BitRate equ d'250000'; Run at 250 kbps ProcessorClock equ d'16' ; Run at16 MHz BrgInit equ (ProcessorClock*d'62500'/BitRate)-1 ; Baud rate generator init with BRGH high (16c74b and later) ; BrgInit equ (ProcessorClock*d'15625'/BitRate)-1 ; Baud rate generator init with BRGH clear. Let the assembler figure it out for you... Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Did you ever do more experimentation on this Harold? Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams Harold M Hallikainen wrote: > > Looking at the datasheet for the PIC16F62x (page 73), it lists the async > serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value (0 to > 255), with BRGH=1. It APPEARS I should be able to make X=0 with Fosc=4MHz > and get 250 kbps. However, if we look on page 75 of the datasheet, it > lists 250kbps as NA with Fosc=4MHz. > Which is correct? -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Nope, never did. I didn't want to rip up my prototype board by replacing the resonator a few more times... So, I'm leaving it at 16 MHz. We buy those resonators by the thousands anyway... Harold On Sun, 27 Jan 2002 20:34:17 -0500 Josh Koffman <listsjoshEraseME.....3MTMP.COM> writes: {Quote hidden}> Did you ever do more experimentation on this Harold? > > Josh > -- > A common mistake that people make when trying to design something > completely foolproof is to underestimate the ingenuity of complete > fools. > -Douglas Adams > > Harold M Hallikainen wrote: > > > > Looking at the datasheet for the PIC16F62x (page 73), it > lists the async > > serial port baud rate as Fosc/(16(x+1) where X is the SPBRG value > (0 to > > 255), with BRGH=1. It APPEARS I should be able to make X=0 with > Fosc=4MHz > > and get 250 kbps. However, if we look on page 75 of the datasheet, > it > > lists 250kbps as NA with Fosc=4MHz. > > Which is correct? > > -- > http://www.piclist.com hint: PICList Posts must start with ONE > topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: > ->Ads > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics