Post by thread:7 segment display HELP

Glendon: you have to be more specific. do you want to know more about 1. serial routine 2. led display multiplexing 3. interrupt Andre Abelian Glendon Turner wrote: {Quote hidden}> Thank you in advance for reading this and hopefully helping me. > > I need to us a 16F84-04 to drive a 3 or 4 digit 7 segment display (common > annode or cathode, doesn't matter). > > I need to be able to send a serial number to the chip (9600,8,N,1) in the > range of 0 to 9999 and have it display it. I think interrupts will be > required because the display needs to be multiplexed and at the same time > needs to check for serial data. > > Not sure on this one. If you can offer any help, I would be very grateful. > > Kind regards > Glendon Turner

On Fri, 3 Jul 1998, Glendon Turner wrote: > Thank you in advance for reading this and hopefully helping me. > > I need to us a 16F84-04 to drive a 3 or 4 digit 7 segment display (common > annode or cathode, doesn't matter). > > I need to be able to send a serial number to the chip (9600,8,N,1) in the > range of 0 to 9999 and have it display it. I think interrupts will be > required because the display needs to be multiplexed and at the same time > needs to check for serial data. At 4 MHz there is enough time available to do 9600 Baud Rx and display multiplexing by polling only. imho an F84 is overkill for this, it should be a C54. Peter

Hi, > > I need to us a 16F84-04 to drive a 3 or 4 digit 7 segment display (common > annode or cathode, doesn't matter). > > I need to be able to send a serial number to the chip (9600,8,N,1) in the > range of 0 to 9999 and have it display it. I think interrupts will be > required because the display needs to be multiplexed and at the same time > needs to check for serial data. > > Not sure on this one. If you can offer any help, I would be very grateful. > I would recommend doing the serial receive under interrupt control and the display multiplexing in your main code. The serial receive code needs the precise timing that the interrupt can offer while the display code timing is not that critical. You could maybe put the display code in the interrupt section as well, but I always try to make Interrupt routines as small as possible - If you don't have to do it under interrupt control, then don't. I would connect the serial receive line to RB0 and set it up to cause an interrupt in the falling edge of the line. This would be used to indicate the start bit. I would then setup the timer 0 to cause interrupts every 1/9600 of a second. The first timer 0 interrupt would then be in the first data bit (D7). The next interrupt will be in D6 and so on. After you have received all the data bits you disable the timer 0 interrupt. (You might want to check the stop bit as well). Graphically it would look like this: A B C D -------- ---- ---- ------------ | | | | | | | |D7|D6 D5 D4|D3|D2|D1 D0 ---- ---------- ---- A - Falling edge causes external interrupt. Disable external interrupt and enable timer 0 interrupts. Set timer 0 to cause interrupt in the middle of next bit (D7). B - First timer 0 interrupt. Sample the receive line. C - Last (or second last if you want to check the stop bit) timer 0 interrupt. Sample the receive line. Now you have the complete byte. D - If you want to check the stop bit, this will be the last timer 0 interrupt. Make sure the receive line is high. Now disable the timer 0 interrupt and re-enable the external interrupt. You are ready now for the next byte. Note: The bits should be sampled in the middle of the bit time for best drift and jitter immunity. Using a 3.6864MHz Xtal, you can get the correct period by using no prescaler and setting bits 5 and 7 of the timer 0 each interrupt. This will cause the timer to count from 160 up to 255 and roll over to 0 each time. This gives a period of 96 instruction cycles, which is what you need (3686400/4/9600 = 96 = 256-160) As you receive a new bytes write then into global variables and if you have reveived a complete number to display, set a flag. The display routine in your main program will check the flag and if set, load the new number into the variables being displayed. The display routine would simply sit in a loop and display one after the other digit (keep the update rate above 50Hz for the whole display). The interrupts in the back while receiveing characters will influence your timing a bit, but it should not be noticable. Hope this helps. Niki

On Fri, 3 Jul 1998 00:43:42 +1000 Glendon Turner <spam_OUTAussiegliderTakeThisOuTBIGPOND.COM> writes: >Thank you in advance for reading this and hopefully helping me. > >I need to us a 16F84-04 to drive a 3 or 4 digit 7 segment display >(common >annode or cathode, doesn't matter). > >I need to be able to send a serial number to the chip (9600,8,N,1) in >the >range of 0 to 9999 and have it display it. I think interrupts will be >required because the display needs to be multiplexed and at the same >time >needs to check for serial data. There are lots of ways to do this application. It's very doable without interrupts, but you'll have to program carefully to keep all the timing right. I'd use a timer interrupt at 9600 Hz which samples the serial input and multiplexes the LEDs. The main program examines the data received and formats it for display. Every time a start bit comes in, the timer would be reset so the interrupts are in the proper phase to sample the data bits. This could be done with a external interrupt or in the main program. The main program won't be doing anything while waiting for a start bit. Changing the phase rather than starting and stopping the interrupt will keep the display miltiplexing almost consistent so incoming data won't make the display flicker. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

Hi, I have another idea; I'm not sure it will solve your problem, but maybe it is a contribution. I had to develop an universal 4-digit 7-segment terminal for different applications with the same interface. I did it a following manner: I took a 16F84 (in some cases it proved as too small; then take a 16C622 or 16C558), and 4 pieces of 74164. The latter are daisy-chained, so I need only the following wires to communicate with the PIC: - a CLOCK line - a DATA line - a RESET line (not important, can be fixed!) - and... If the display changes, it leads to some flicker. If it is undesirable, I took ONE transistor to control the common cathode of ALL digits, and this transistor is controlled with PIC. And what is very fine here: - no multiplexing - speed is incredible - the display is done with a single SEROUT command of the PicBasic PRO. On the receiving side I don't deal with interrupts. Instead, I use hardware handshake like CTS. Of course, it needed some time to set up the conversion table. I built some intelligency in my terminal: it is controlled by escape sequences, so I can control how to interpret the data, e. g. 1 letter + 3 digit 1 letter + 1 byte to be rescaled to 0..999 all characters all hex data etc. Imre On Thu, 2 Jul 1998, Mike Keitz wrote: {Quote hidden}> On Fri, 3 Jul 1998 00:43:42 +1000 Glendon Turner > <.....AussiegliderKILLspam@spam@BIGPOND.COM> writes: > >Thank you in advance for reading this and hopefully helping me. > > > >I need to us a 16F84-04 to drive a 3 or 4 digit 7 segment display > >(common > >annode or cathode, doesn't matter). > > > >I need to be able to send a serial number to the chip (9600,8,N,1) in > >the > >range of 0 to 9999 and have it display it. I think interrupts will be > >required because the display needs to be multiplexed and at the same > >time > >needs to check for serial data. > > There are lots of ways to do this application. It's very doable without > interrupts, but you'll have to program carefully to keep all the timing > right. I'd use a timer interrupt at 9600 Hz which samples the serial > input and multiplexes the LEDs. The main program examines the data > received and formats it for display. Every time a start bit comes in, > the timer would be reset so the interrupts are in the proper phase to > sample the data bits. This could be done with a external interrupt or in > the main program. The main program won't be doing anything while waiting > for a start bit. Changing the phase rather than starting and stopping > the interrupt will keep the display miltiplexing almost consistent so > incoming data won't make the display flicker. > > _____________________________________________________________________ > You don't need to buy Internet access to use free Internet e-mail. > Get completely free e-mail from Juno at http://www.juno.com > Or call Juno at (800) 654-JUNO [654-5866] > >

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>> >I need to us a 16F84-04 to drive a 3 or 4 digit 7 segment display >> >(common >> >annode or cathode, doesn't matter). >> > >> >I need to be able to send a serial number to the chip (9600,8,N,1) in >> >the >> >range of 0 to 9999 and have it display it. I think interrupts will be >> >required because the display needs to be multiplexed and at the same >> >time >> >needs to check for serial data. One possibility is to use the Philips SAA1064 chip, a 4-digit LED-driver with I2C-Bus interface. It's not async serial, but it does give you two wire (plus ground) comms and it handles all the multiplexing, decoding and everything. The Philips website has the datasheet. Stephen.

At 14:23 4.7.1998 +1200, you wrote: >One possibility is to use the Philips SAA1064 chip, a 4-digit LED-driver >with I2C-Bus interface. It's not async serial, but it does give you two >wire (plus ground) comms and it handles all the multiplexing, decoding and >everything. > >The Philips website has the datasheet. Yep, I used this chip several times. But there is a problem now, because Philips stopped the production of these chips and I was not able to find any equivalent. Finally, I was lucky three weeks ago and I got last 10 SAA1064 chips from one supplier here. But I am affraid that these are the last one :-(( PavelK ************************************************************************** * Pavel Korensky * * DATOR3 LAN Services spol. s r.o. * * Modranska 1895/17, 143 00, Prague 4, Czech Republic * * * * PGP Key fingerprint: F3 E1 AE BC 34 18 CB A6 CC D0 DA 9E 79 03 41 D4 * * * * SUMMA SCIENTIA - NIHIL SCIRE * **************************************************************************