please dont rip this site

Control 3 (expandable to 8) 7 segment LED displays with 3 io pins and a driver IC

by Ken Mathis

Ken Mathis of ASC shares this code:

;FILE NAME:MAX7219
;Date:June 16, 2004
;Programmer:Ken Mathis
;Purpose of this program is to control several seven segment displays using the MAX7219
;seven segment display driver IC. The seven segment displays are multiplexed with the 
;7219 and are commone cathode type displays.


;This test code controls only 3 seven segment displays. The code can easily be expanded 
;for the max7219 to control up to 8 seven segment displays while consuming only 3 SX
;output pins
;Where appropriate, explanations are provided to account for more than 3 seven segment displays

;This configuration uses the SX internal oscillator as the timimg for shifting data
;out is not critical
;-----[Assembler directives]---------------------------------------
ifdef __SASM
	DEVICE	SX18L, STACKX, OPTIONX
	IRC_CAL	IRC_FAST
	FREQ	4_000_000
else
	DEVICE	SX18AC, OPTIONX
endif
DEVICE	TURBO, OSC4MHZ
RESET	START

;-----[Define variables and constants]------------------------------
org	$07		;$07 is first free variable space
Decode	ds	2	;assign 2 bytes of space for Decode - 7 & 8
ShtDn	ds	2	;assign 2 bytes of space for Shutdown - 9 & A
ScnLmt	ds	2	;assign 2 bytes of space for Scan Limit - B & C
Inten	ds	2	;assign 2 bytes of space for Intensity - D & E
bitcnt	ds	1	;assign 1 byte of space for bit counter - F

;dig0, dig1, & dig2 represent three 7 segment displays with a common cathode and
;dig0 is the least significant display
dig0	ds	2	;assign 2 bytes of space for Digit 0 - 10 & 11
dig1	ds	2	;assign 2 bytes of space for Digit 1 - 12 & 13
dig2	ds	2	;assign 2 bytes of space for Digit 2 - 14 & 15
;To display more digits variable manes MUST be added here sequentially
;after dig2 for the code to properly work.


; !!! IF 8 SEVEN SEGMENT DISPLAYS ARE USED, there will be no more room
;for the word counter (wrdcnt) in bank one. To avoid switching banks in 
;this circumstance, the upper or lower byte of any of the initialization 
;words (Decode, ShtDn, ScnLmt, or Inten) can be reused/reloaded with
;the appropriate value after the initialization if finished. A comment
;will be shown where to reload Decode if needed

wrdcnt	ds	1	;assign 1 byte of space for word counter - 16


;----[Define symbolic pin names]---------------------------------------


data	EQU	rb.1	;data pin connects to pin 1 of 7219
clock	EQU	rb.2	;clock pin connects to 13 of 7219
load	EQU	rb.3	;load pin connects to 12 of 7219

;-----[calls should be placed on first page between org $000 and org $100]--
org	$000

;5uS delay - generated using the delay code generator at sxlist.com
del_5uS
	jmp	$+1
	jmp	$+1
	jmp	$+1
	jmp	$+1
	nop
	nop
	ret

;sub to shift out msbit of each byte into carry
rotate
	rl	ind	;move msbit into carry 
	jc	high	;if carry is high jump to high
	clrb	data	;if carry is low ensure data pin is low
	jmp	$+2	;jump 2 lines
high
	setb	data	;make data pin high
	nop		;no operation
	ret

;clock pulse generation to shift data out of SX into max 7219
shiftout
	call	del_5uS	;5 uS set-up time
	setb	clock	;make clock (rb.2) high
	call	del_5uS	;5 uS hold time
	clrb	clock	;make clock low
	ret		;return

;-----[MAIN PROGRAM]------------------------------------------------------------
org	$100

Start			;reset point	

;-------[I/O port setting]------------------------------------------------------
	mode	$0f	;set mode for port direction
	mov	w,#$0
	mov	!ra,w	; all ra ports output
	mov	w,#$00
	mov	!rb,w	;all rb ports output



;-------[prepare variables for initialization of max7219]-----------------------
;mov w,#$XX loads the w register with hex value 
;mov NAME,w loads value of w into variable name
;Later in this program the initiazation is explained in detail
	mov	w,#$09
	mov	Decode,w
	mov	Inten+1,w
	mov	w,#$0f
	mov	Decode+1,w
	mov	w,#$10
	mov	bitcnt,w
	mov	w,#$0c
	mov	shtdn,w
	mov	w,#$01
	mov	shtdn+1,w
	mov	dig0,w
	mov	w,#$0b
	mov	scnlmt,w
	mov	w,#$02
	mov	scnlmt+1,w
	mov	dig1,w
	mov	w,#$0a
	mov	inten,w
	mov	w,#$03
	mov	dig2,w
	mov	w,#$04
	mov	wrdcnt,w


;point to first register that will hold data to shift out which
;is Decode at address $07. NOTE that this is a SX18 and does not have an RC
;port.	
	mov	w,#$07	
	mov	fsr,w

;-------[The program currently causes display to load 4 to each digit. To test a
;different value, change four to any digit 0 to 9. Your actual program will load 
;dig0+1, dig1+1 and dig2+1 with some dynamic data.
	mov	w,#$04
	mov	dig0+1,w
	mov	dig1+1,w
	mov	dig2+1,w


;------[MAX7219 Operation]----------------------------------------------------
;The 7219 must first be initialized. Initialization is done by sending serial
;data to the IC. Four 16 bit values sent will complete the initialization.

;To send a 16 bit value load is brought LOW, then each of 16 bits (msb 1st) is 
;clocked into the IC, and load is then brought HIGH to complete the shifting 
;of 16 bits into the device

;For each word sent to the IC, the most significant byte is the address and the
;lower byte sets the option for each particular function.
;For the descriptions that follow values will be shown as $Xx. The upper case x
;represents the upper nibble and the value is "don't care"

;DECODE MODE - Address $X9 
;Options	$X0 = No decoding
;		$X1 = Decode digit 0 (BCD)
;		$XF = Decode digits 0-3
;		$FF = Decode digits 0-7
;Sending $090F sets decode mode to enable digits 0-3 and unstucts that the least
;sig nibble is BCD 

;SHUTDOWN MODE - Address $XC
;Options	$X0 = Shutdown
;		$X1 = Normal Operation
;Sending $0C01 sets the IC for normal operation

;SCANLIMIT - Address $XB
;Options	$Xx where the least significant nibble sets the number of digits
;		to enable. digit 0, x = 0. digits 0 & 1 x = 1. digits 0, 1, & 2 x = 2
;Sending $0B02 enbables digts 0, 1 & 2
;Sending $0B07 enables all 8 digits

;INTENSITY - Address $XA
;Options	$00 = minimum intensity
;		$FF = maximum intensity
;		See MAX7219 data sheet for resistor selection and current


;----[set up SX controll pins]--------------------------------------------------------
	clrb	data		;make data pin low
	clrb	clock		;make clock pin low
	setb	load		;make load pin high
	call	del_5uS		;wait 5 uS

;----[Start of routine to send out first 16 bits]-------------------------------------
	clrb	load		;enable 7219 to start accepting serial data.
j1
	call	rotate		;call routine to move msbit into carry and set data pin 
				;high or low depending on state of bit carried out
	call	shiftout	;call routine to shift data bit to 7219
	dec	bitcnt		;decrement bit counter
	cjne	bitcnt,#8,j2	;check if 8 bits have been sent out
	inc	fsr		;if 8 bits were sent, increment fsr to point to next 
				;register
	jmp	$-8		;move back up to call rotate
j2
	cja	bitcnt,#0,j1	;check of bit counter is at zero (16 bits shifted out?)
	setb	load		;if 16 bits shifted out, load them into the 7219
	dec	wrdcnt		;check if the 4 initialization words shifted out
	cja	wrdcnt,#0,j3	;if word counter is above 0, jump to j3
	jmp	$+5		;if the 4 initialization words shifted out jump down 5 lines
j3	
	mov	w,#$10		;reload bit counter with 16
	mov	bitcnt,w	;reload bit counter with 16
	inc	fsr		;increment fsr to point to the next register
	jmp	$-$18		;jump up to the "clrb load" instruction to start another
				;sequence of shifting out 16 more bits


;-----[shift actual data into max7219]---------
;Data is sent to the 7219 in the same manner as the initialization described above.
;load is brought LOW, 16 bits clocked into device and load is brought HIGH to complete
;the loading of one digit.

;For each digit, the upper byte of 16 bits is the address of the digit and the lower
;byte is the value sent to the 7 segment. This value is either BCD or the "word" to control
;each of the 8 segments (decimal point). Remember that DECODE MODE determines how to 
;use the lower byte

;For	digit 0 the address is $01
;	digit 1 the address is $02
;	digit 2 the address is $03

;If decode mode was selected sending the 16 bit value of $0207 will tell the IC that
;digit number 1 gets a value of 7


	mov	w,#$10
	mov	fsr,w		;point to first address of digit 0 holding the most sig byte
	mov	bitcnt,w	;load the bit counter with 16

;If using 8 seven segment displays as decribed above, comment out the next two lines 
	mov	w,#$03		;since three digits are used in this example, wrdcnt is loaded w/3
	mov	wrdcnt,w
;Use these next two lines if 8 seven segments are used.
;	mov	w,#$08
;	mov	Decode,w

;----[Start of routine to send out first 16 bits of TEST data]-------------------------------------
;The rest of this code is exactly the same as the initialization code, so no comments added here.
;see initialzation above for comments.
	clrb	load		
j4
	call	rotate
	call	shiftout
	dec	bitcnt
	cjne	bitcnt,#8,j5
	inc	fsr
	jmp	$-8
j5
	cja	bitcnt,#0,j4
	setb	load
;If using 8 seven segment displays as decribed above, comment out the next two lines 
	dec	wrdcnt
	cja	wrdcnt,#0,j6

;Use these next two lines 
;	dec	Decode
;	cja	Decode,#0,j6

	jmp	$+5
j6	
	mov	w,#$10
	mov	bitcnt,w
	inc	fsr
	jmp	$-$18

	setb	load
	sleep

END

file: /Techref/scenix/lib/io/dev/led/multi7seg3io-km.htm, 9KB, , updated: 2004/12/25 12:12, local time: 2024/12/24 08:50,
TOP NEW HELP FIND: 
3.22.27.41:LOG IN

 ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE!

<A HREF="http://techref.massmind.org/Techref/scenix/lib/io/dev/led/multi7seg3io-km.htm"> Control 3 (expandable to 8) 7 segment LED displays with 3 io pins and a driver IC </A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.


Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

 

Welcome to massmind.org!

 

Welcome to techref.massmind.org!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .