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???
07/27/04 09:07
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#74953 - RE: Need help with LED display
Responding to: ???'s previous message
hi,

i intend to use a 7x5 matrix for each charaster while the complete board will have at least 32 or 48 columns.

Do you mean 32 or 48 characters when say columns? By other words, complete board will contain 160 or 240 columns, right?
If so, I can suggest you to use Allegro LED drivers production.
For example, 32-bit serial input latched drivers UCN5832 or UCN5833. For 32 characters you have to buy 32*5/32 = 5 devices. Outputs of these ICs should be connected to 160 columns of LED Dot Matrixes through resistors.
As well, you need with 7 power source drivers which may be done with transistors. These source drivers provide power to seven rows of all matrixes.

Now the idea is high speed refresh of your LED Dot Matrixes: you shift out 160 bits into UCN, switch off all transistors, strobe shifted data into output latches then switch on the first row. After some time, do the same for second row, then for third, etc upto seven. After all, start the cycle again from the first row.

There is speed requirement: I suggest to keep refresh rate at 100Hz or above, i.e. you should run refresh routine at each 1/(7*100) =~1,5 ms. Shifting of 160 bits takes some time:
REFRESH_DATA	EQU	0x40
RSH_DAT		EQU	P1.0
RSH_CLK		EQU	P1.1
; ...

RSH_MATRIX:
	MOV	R0,#REFRESH_DATA
RSH_NEXT_BYTE:
	MOV	A,@R0
	MOV	R7,#8
RSH_NEXT_BIT:
	CLR	RSH_CLK	
	RRC	A
	MOV	RSH_DAT,C
	SETB	RSH_CLK	
	DJNZ	R7,RSH_NEXT_BIT
	INC	R0
	CJNE	R0,#(REFRESH_DATA+20),RSH_NEXT_BYTE
With standard 8051 it takes above 1200 machive cycles. As result, with OSC=12MHz such refresh subroutine "eats" 1,2ms and, as result, you lost all productivity of MCU (no time to do something else). Solutions:
- use crystal/oscillator with higher frequency;
- use high productivity MCU (with x2 mode etc);
- use UART at mode 0 (shift register) to shift out refresh data;
- use external CPLD+RAM for refresh task;
- use "parallel refresh".
At last suggestion, I mean that you may replace each UCN5832 with four 6A595 (or TPIC6A595). As result, you will have 20 ICs. Then you group them to 4 streams with 5 chips in each. Now, refresh routine clocks out the nibble instead of bit:
REFRESH_DATA	EQU	0x40
RSH_OUT		EQU	P2		; 4 bits are used
RSH_CLK		EQU	P1.1

; ...

RSH_MATRIX:
	MOV	R0,#REFRESH_DATA
RSH_NEXT_BYTE:
	MOV	A,@R0
	CLR	RSH_CLK
	MOV	RSH_OUT,A
	SETB	RSH_CLK
	SWAP	A
	CLR	RSH_CLK
	MOV	RSH_OUT,A
	SETB	RSH_CLK
	INC	R0
	CJNE	R0,#(REFRESH_DATA+20),RSH_NEXT_BYTE
This routine takes about 220 machive cycles only.

As well, you should think about power: each row contains 160 LEDs; each LED sink about 50mA (or more) in peak. So row current is about 8A.

i have just completed reading the assembly language and instruction set of the 8052
Please, I need all the help i can get as i hope to complete this project within the next one month.


One month? Good luck then. Schematic, PCB, programming...

Regards,
Oleg

List of 62 messages in thread
TopicAuthorDate
Need help with LED display            01/01/70 00:00      
   RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
         RE: Need help with LED display            01/01/70 00:00      
            RE: Need help with LED display            01/01/70 00:00      
               RE: Need help with LED display            01/01/70 00:00      
                  RE: Need help with LED display            01/01/70 00:00      
                     RE: Need help with LED display            01/01/70 00:00      
                        RE: Need help with LED display            01/01/70 00:00      
                           RE: scroll            01/01/70 00:00      
                           RE: Need help with LED display            01/01/70 00:00      
                              RE: Need help with LED display            01/01/70 00:00      
                                 RE: Need help with LED display            01/01/70 00:00      
                                 RE: Need help with LED display            01/01/70 00:00      
                                 READY FOR SCHEMATICS            01/01/70 00:00      
                                    RE: READY FOR SCHEMATICS            01/01/70 00:00      
                                       RE: READY FOR SCHEMATICS            01/01/70 00:00      
                                       RE: READY FOR SCHEMATICS            01/01/70 00:00      
                                          RE: READY FOR SCHEMATICS            01/01/70 00:00      
                                             RE: READY FOR SCHEMATICS            01/01/70 00:00      
                                                RE: READY FOR SCHEMATICS            01/01/70 00:00      
                                                   construction of marix            01/01/70 00:00      
                                                      RE: construction of marix            01/01/70 00:00      
                                                      RE: construction of marix            01/01/70 00:00      
                                    No reason to shout!            01/01/70 00:00      
                              RE: Need help with LED display            01/01/70 00:00      
                                 RE: Need help with LED display            01/01/70 00:00      
                                    RE: Need help with LED display            01/01/70 00:00      
                                 RE: Need help with LED display            01/01/70 00:00      
                                    RE: Need help with LED display            01/01/70 00:00      
         RE: Need help with LED display            01/01/70 00:00      
   Multiplexing scheme            01/01/70 00:00      
      RE: Multiplexing scheme            01/01/70 00:00      
         RE: Multiplexing scheme            01/01/70 00:00      
            RE: Multiplexing scheme            01/01/70 00:00      
            RE: Multiplexing scheme            01/01/70 00:00      
               RE: Multiplexing scheme            01/01/70 00:00      
                  RE: Multiplexing scheme            01/01/70 00:00      
                     RE: Multiplexing scheme            01/01/70 00:00      
                        RE: Multiplexing scheme            01/01/70 00:00      
                           RE: Multiplexing scheme            01/01/70 00:00      
   RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
         RE: Need help with LED display            01/01/70 00:00      
            RE: Need help with LED display            01/01/70 00:00      
               RE: Need help with LED display            01/01/70 00:00      
               RE: Need help with LED display            01/01/70 00:00      
                  RE: Need help with LED display            01/01/70 00:00      
                     RE: 100Hz            01/01/70 00:00      
   RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
      RE: Need help with LED display            01/01/70 00:00      
         RE: Need help with LED display            01/01/70 00:00      
            RE: Need help with LED display            01/01/70 00:00      
      how to do calculations            01/01/70 00:00      
         RE: how to do calculations            01/01/70 00:00      
            RE: how to do calculations            01/01/70 00:00      
               RE: how to do calculations            01/01/70 00:00      
               RE: how to do calculations            01/01/70 00:00      

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