Looking for simple way to interface BCD to serial (RS232)
in [Design]
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From: John Fields on 30 Dec 2009 15:18 On Tue, 29 Dec 2009 22:56:12 -0500, RFI-EMI-GUY <Rhyolite(a)NETTALLY.COM> wrote: >I have a hardcopy of the complete manual, theory, schematics, parts >lists. Unfortunately no board layouts. --- Can you post the schematics, please? JF
From: RFI-EMI-GUY on 30 Dec 2009 20:38 mike wrote: > RFI-EMI-GUY 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. >> > Implementation details can be interesting, but only if the concept is > sound. > Check my math... > 300 baud is 30 characters a second, give or take... > You want 3 digits updated 300 times a second. > that's 900 characters a second through a 30 character/second pipe. > 4800 baud is about half of what you need for throughput. > You can almost get there if you mux two digits into one RS232 character. > What am I misunderstanding? > > As for implementation, a microcontroller is gonna be fewer parts, > smaller size, easier implementation. These days, it's hard to find > a project that can be done better/faster/cheaper without one. (I repeat) 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: petrus bitbyter on 31 Dec 2009 06:12 "RFI-EMI-GUY" <Rhyolite(a)NETTALLY.COM> schreef in bericht news:4b3c0090$0$4962$9a6e19ea(a)unlimited.newshosting.com... > mike wrote: >> RFI-EMI-GUY 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. >>> >> Implementation details can be interesting, but only if the concept is >> sound. >> Check my math... >> 300 baud is 30 characters a second, give or take... >> You want 3 digits updated 300 times a second. >> that's 900 characters a second through a 30 character/second pipe. >> 4800 baud is about half of what you need for throughput. >> You can almost get there if you mux two digits into one RS232 character. >> What am I misunderstanding? >> >> As for implementation, a microcontroller is gonna be fewer parts, >> smaller size, easier implementation. These days, it's hard to find >> a project that can be done better/faster/cheaper without one. > > (I repeat) > > 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 As you have the schematic why not use the solution provided there? Or is this part left out? But even then you'd find some remnants of the interface that'll make it much easier to provide a solution. Supposing you have a signal that initiates the display update (and there must be some) the next algorithm will due (either in hardware or in a micro): 1. Wait for display update 2. Wait for leading edge of address pin 1 3. Load digit 1 in shift register and shift it out 4. Wait for leading edge of address pin 2 5. Load digit 2 in shift register and shift it out 6. Wait for leading edge of address pin 3 7. Load digit 3 in shift register and shift it out 8. Goto 1 If you really want a hardware only solution, the schematics of John Fields will give you a headstart. petrus bitbyter
From: JosephKK on 2 Jan 2010 16:33 On Sun, 27 Dec 2009 18:29:16 -0800, Joerg <invalid(a)invalid.invalid> wrote: >RFI-EMI-GUY wrote: >> don wrote: >>> RFI-EMI-GUY 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. >>>> >>> Do you docs on the outputs ? >>> >>> don >> >> >> I think you are asking the specs of the driving chip? 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). >> > >That will not be so trivial because this is a chip that drives the LED >in muxed fashion. Which immediatly leads to the next question, what is on the other side of that chip?
From: John Fields on 3 Jan 2010 18:48
On Sat, 02 Jan 2010 13:33:49 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Sun, 27 Dec 2009 18:29:16 -0800, Joerg <invalid(a)invalid.invalid> wrote: > >>RFI-EMI-GUY wrote: >>> don wrote: >>>> RFI-EMI-GUY 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. >>>>> >>>> Do you docs on the outputs ? >>>> >>>> don >>> >>> >>> I think you are asking the specs of the driving chip? 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). >>> >> >>That will not be so trivial because this is a chip that drives the LED >>in muxed fashion. > >Which immediatly leads to the next question, what is on the other side of that chip? --- If you're talking about the driven side of the 7217, it shouldn't make much difference since all that's being output from the chip is four parallel bits of BCD date along with four single-bit strobes with edges that go low when the BCD data is valid. The job, therefore, is to assemble the four output data bits, the strobe bit, the start and stop bits, and to send all of them as a 10 bit serial word formatted as RS-232 TRANSMITTED DATA to a receiver somewhere which is expecting it to come in at a particular bit rate. JF |