max7219 help

Timmy

Hi folks,

just after any suggestions as to why i am unable to get my max7219 to display any data on my 7-seg display. I suspect it is a coding error (not my strong area). My circuit is identical to the one described in Nuts n volts #10 however I am using a BS2 instead of a BS1. I have thoroughly checked my circuit and checked to see if my stamp has dead pins.

my code is as follows, very simple initially to get started.

' {$STAMP BS2}
'display char's on a 7-seg display with a max7219

DPin CON 8 ' data to MAX7219
Load CON 9 ' latch
Clock CON 10 ' shift clock to MAX7219

text VAR Byte

'----initialize
LOW dpin: LOW load: LOW clock '
PAUSE 100

'----main prog

text = 3

start:
SHIFTOUT Dpin,Clock,MSBFIRST, [noparse][[/noparse] text]
PULSOUT load, 6



any suggestions most appreciated,

timmy!

Jon Williams

There's more to initializing the MAX7219 than you're doing. This (old) StampWorks project will help: http://www.parallax.com/dl/docs/books/sw/exp/sw29.pdf

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Jon Williams
Applications Engineer, Parallax

Timmy

thanks for the article jon. I've got the display operating now, which is a relief, I just now need to slowly trawl through the program to understand how the initialisation loop routine works.

thanks for the speedy reply,

timmy!

KenM

Tim,

This may help to decipher the initialization....



;

---

[noparse][[/noparse]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 instructs 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

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Ken

Timmy

Thanks Ken for the info. really helpful.

timmy!