Looking for simple way to interface BCD to serial (RS232)
in [Design]
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From: RFI-EMI-GUY on 28 Dec 2009 21:48 MooseFET wrote: snip > I think it would be easier without the FIFO UART. You just want a > signal that looks like the RS-232. You don't really need a RS-232 > receive function at all unless you want to use it to set the Baud > rate. > I need compatibility with software that expects RS232 , I need to send the appropriate bits, although the RX could be used to program the PIC I guess. -- Joe Leikhim K4SAT "The RFI-EMI-GUY"� "Use only Genuine Interocitor Parts" Tom Servo ;-P
From: RFI-EMI-GUY on 28 Dec 2009 22:03 petrus bitbyter wrote: > "RFI-EMI-GUY" <Rhyolite(a)NETTALLY.COM> schreef in bericht > news:4b3815d7$0$4949$9a6e19ea(a)unlimited.newshosting.com... >> John Fields wrote: >>> On Sun, 27 Dec 2009 16:52:22 -0500, RFI-EMI-GUY <Rhyolite(a)NETTALLY.COM> >>> wrote: >>> >>>> I have a device that has a three digit LED display. The chip that drives >>>> the LED also has four Binary Weighted outputs (1,2,4,8) and three >>>> address pins for 100's, 10's and units. I want to drive a FIFO UART of >>>> some sort to output an RS232 stream so that this device can update a >>>> software program. Baud rate 300 to 4800 range would be nice if possible. >>>> >>>> The updates are about 300/second >>>> >>>> Is there a real simple hardware FIFO UART that can do this without a lot >>>> of extra hardware. I don't want a software fix unless I can do it in >>>> PicAxe and can find code written. >>>> >>>> Off the shelf products OK I don't want to reinvent the wheel. >>> --- >>> The way I'd do it would be to broadside load a 10 bit parallel-in >>> serial-out shift registers with the BCD data, the digit data, a stop and >>> a start bit, and then shift the data out serially to the RS-232 input of >>> whatever's updating your software program. >>> >>> If the broadside data into the shifter is updating at about 300Hz, >>> that's about 3.33ms, so to shift it all out before the next update comes >>> along would require a bit clock at least 10 times faster than that, or >>> about 333�s/3.3kHz. >>> >>> Duck soup, maybe. ;) >>> >>> What's the chip that's driving the display? >>> >>> JF >> Its an ICM7217IJI Common Cathode 4 LED Display/Programmable Up/Down >> Counter. The BCD I/O pins and the segment drivers b, d and f (d1, d2, d3) >> used to select 100's. 10's and units (I may have order reversed). >> >> -- >> Joe Leikhim K4SAT >> "The RFI-EMI-GUY"� >> >> "Use only Genuine Interocitor Parts" Tom Servo ;-P > > > Hmm... So 300 updates/s * 3 digits * 10 bits makes 9000bps. Even 4800Bd will > not be enough you will need at least 9600Bd. > > Meanwhile, the scanrate is some 2500 digits/s. To send them all you would > need at least 25kbps. There is no need to send them all but you will need to > do some buffering and selection at the transmitting side. > > Another complication is the updating itself. For all I can see there is no > other way to detect an update but finding some digit(s) changed. That's to > say unless you can catch the /STORE signal. But even then there seems no way > to predict at what time during the scanning of the three digits that signal > occurs. So you need to store two sets of digits and compare them. Only when > two successive sets are equal you may have a valid output. Otherwise one or > even both may be deformed. > > I consider the chance to find an of the shelf solution pretty small. > Building a circuit that account for all details mentioned requires quite a > lot of hardware. Today, designers will use some programmable device like a > PLD or an FPGA. But the moment you're going to program a device you may get > a micro as well. A PIC16F628 or a PICAXE-28X2 will do the job... But yes, it > need to be programmed. > > If you want me to do something like that for you, mail me at > petrusdotbitbyterathotmaildotcom. > > petrus bitbyter > > The device I am talking about is a Doppler Systems DDF4002 doppler direction finder. It is an older modele that once had a serial interface option which is no longer available. Your observation about the update rate is quite correct and is covered in the manual for the DDF4002, The theory section of the manual describes almost exactly the data rate assumptions you have stated but qualifies it with: "However, the message is initiated only when the display is updated. Since this occurs at a maximum rate of 1/1.875 (0.533) seconds, ample time exists between characters and between messages to prevent overrunning. There is also a later hardware mod to raise the 16X clock (4800 Hz from main board) to 38,400 Hz to provide 2400 baud. -- Joe Leikhim K4SAT "The RFI-EMI-GUY"� "Use only Genuine Interocitor Parts" Tom Servo ;-P
From: RFI-EMI-GUY on 28 Dec 2009 22:07 whit3rd wrote: > On Dec 27, 1:52 pm, RFI-EMI-GUY <Rhyol...(a)NETTALLY.COM> wrote: >> I have a device that has a three digit LED display. The chip that drives >> the LED also has four Binary Weighted outputs (1,2,4,8) and three >> address pins for 100's, 10's and units. I want to drive a FIFO UART... > >> Is there a real simple hardware FIFO UART that can do this > > The RS-232 requirement will be somewhat awkward, depending > on what power supplies are available; have you considered > USB instead? The FTDI device "FT245R" is a FIFO-input > USB slave device, with software support. I'd imagine you > can clear the FIFO and clock eight bits of address-and-BCD > data (four BCD bits and three 'digit enable' flags) as the > display is updated. Maybe the 'extra' bit could be used for > overflow or other error indicator. I understand that I may need a bi-polar power supply and line driver like a DF1488 am wary of USB beacause I don't know if any of the legacy amateur software that this will be used for has drivers for USB. Tell me more however. -- Joe Leikhim K4SAT "The RFI-EMI-GUY"� "Use only Genuine Interocitor Parts" Tom Servo ;-P
From: petrus bitbyter on 29 Dec 2009 04:30 "RFI-EMI-GUY" <Rhyolite(a)NETTALLY.COM> schreef in bericht news:4b397197$0$4964$9a6e19ea(a)unlimited.newshosting.com... > petrus bitbyter wrote: >> "RFI-EMI-GUY" <Rhyolite(a)NETTALLY.COM> schreef in bericht >> news:4b3815d7$0$4949$9a6e19ea(a)unlimited.newshosting.com... >>> John Fields wrote: >>>> On Sun, 27 Dec 2009 16:52:22 -0500, RFI-EMI-GUY <Rhyolite(a)NETTALLY.COM> >>>> wrote: >>>> >>>>> I have a device that has a three digit LED display. The chip that >>>>> drives the LED also has four Binary Weighted outputs (1,2,4,8) and >>>>> three address pins for 100's, 10's and units. I want to drive a FIFO >>>>> UART of some sort to output an RS232 stream so that this device can >>>>> update a software program. Baud rate 300 to 4800 range would be nice >>>>> if possible. >>>>> >>>>> The updates are about 300/second >>>>> >>>>> Is there a real simple hardware FIFO UART that can do this without a >>>>> lot of extra hardware. I don't want a software fix unless I can do it >>>>> in PicAxe and can find code written. >>>>> >>>>> Off the shelf products OK I don't want to reinvent the wheel. >>>> --- >>>> The way I'd do it would be to broadside load a 10 bit parallel-in >>>> serial-out shift registers with the BCD data, the digit data, a stop >>>> and >>>> a start bit, and then shift the data out serially to the RS-232 input >>>> of >>>> whatever's updating your software program. >>>> >>>> If the broadside data into the shifter is updating at about 300Hz, >>>> that's about 3.33ms, so to shift it all out before the next update >>>> comes >>>> along would require a bit clock at least 10 times faster than that, or >>>> about 333�s/3.3kHz. >>>> >>>> Duck soup, maybe. ;) >>>> >>>> What's the chip that's driving the display? >>>> >>>> JF >>> Its an ICM7217IJI Common Cathode 4 LED Display/Programmable Up/Down >>> Counter. The BCD I/O pins and the segment drivers b, d and f (d1, d2, >>> d3) used to select 100's. 10's and units (I may have order reversed). >>> >>> -- >>> Joe Leikhim K4SAT >>> "The RFI-EMI-GUY"� >>> >>> "Use only Genuine Interocitor Parts" Tom Servo ;-P >> >> >> Hmm... So 300 updates/s * 3 digits * 10 bits makes 9000bps. Even 4800Bd >> will not be enough you will need at least 9600Bd. >> >> Meanwhile, the scanrate is some 2500 digits/s. To send them all you would >> need at least 25kbps. There is no need to send them all but you will need >> to do some buffering and selection at the transmitting side. >> >> Another complication is the updating itself. For all I can see there is >> no other way to detect an update but finding some digit(s) changed. >> That's to say unless you can catch the /STORE signal. But even then there >> seems no way to predict at what time during the scanning of the three >> digits that signal occurs. So you need to store two sets of digits and >> compare them. Only when two successive sets are equal you may have a >> valid output. Otherwise one or even both may be deformed. >> >> I consider the chance to find an of the shelf solution pretty small. >> Building a circuit that account for all details mentioned requires quite >> a lot of hardware. Today, designers will use some programmable device >> like a PLD or an FPGA. But the moment you're going to program a device >> you may get a micro as well. A PIC16F628 or a PICAXE-28X2 will do the >> job... But yes, it need to be programmed. >> >> If you want me to do something like that for you, mail me at >> petrusdotbitbyterathotmaildotcom. >> >> petrus bitbyter > > The device I am talking about is a Doppler Systems DDF4002 doppler > direction finder. It is an older modele that once had a serial interface > option which is no longer available. > > Your observation about the update rate is quite correct and is covered in > the manual for the DDF4002, The theory section of the manual describes > almost exactly the data rate assumptions you have stated but qualifies it > with: > > "However, the message is initiated only when the display is updated. Since > this occurs at a maximum rate of 1/1.875 (0.533) seconds, ample time > exists between characters and between messages to prevent overrunning. > > There is also a later hardware mod to raise the 16X clock (4800 Hz from > main board) to 38,400 Hz to provide 2400 baud. > > -- > Joe Leikhim K4SAT > "The RFI-EMI-GUY"� > > "Use only Genuine Interocitor Parts" Tom Servo ;-P Found a manual of the DDF1. That's a kits description but two important pages i.e.18 and 19 are carefully wiped out. Maybe a predecessor of the DDF4002 (or not). Current information at Doppler Systems Inc. starts at 6000 series. No trace of the 4002 ever existed. Does your manual contain a schematic or print layout? petrus bitbyter
From: MooseFET on 29 Dec 2009 09:55
On Dec 28, 6:48 pm, RFI-EMI-GUY <Rhyol...(a)NETTALLY.COM> wrote: > MooseFET wrote: > > snip > > > I think it would be easier without the FIFO UART. You just want a > > signal that looks like the RS-232. You don't really need a RS-232 > > receive function at all unless you want to use it to set the Baud > > rate. > > I need compatibility with software that expects RS232 , I need to send > the appropriate bits, although the RX could be used to program the PIC I > guess. Yes you need to be compatible with software that expects RS-232. This means that you do not need a UART chip. All a UART chip does is make a signal wiggle up and down with a certain pattern. It is often easier to just make the signal you want rather than adapt to some chip. Example: A simple counter driving a 4051 MUX or two or three can make perfectly good RS-232 data out of some small collection of logic signals. |