In SX Microcontrollers, SX/B Compiler and SX-Key Tool, johncouture wrote:

Using a MAX7219 with SHIFTOUT
=============================

 

Definition:

A MAX7219 is a chip that enables you to control up to
eight 7 segement digits using just three pins on your
mcu.  (Datasheet attached).

 

Problem:

   Just trying to setup a simple test where I control the 
   7 seg digits on the Prof Dev Board using a MAX7219.

   (source code attached)
   
Setup:
   SX28
   Prof Dev Board (PDB)
   MAX7219
   
Connections: (pin connections pg 1)
   RB.0 is DQ   (pin 01 on 7219)
   RB.1 is LOAD (pin 12)
   RB.2 is Clk  (pin 13)
   
   7 seg displays connected (seg A-G)
   digit control connected (dig 0-4)   
   power (19), ground (4,9)
   pull-high resistor, 10k, (18)

   DOUT (24) connected to an LED0 on PDB   
   
Experiment:
   1) Timing Diagram (pg 6) says to set LOAD to
      LOW during data send and then toggle HIGH
      once done sending 16 bits.
      
   2) 7219 expects 16 bit packet (see pg 6),
      the MSB 8 are control, LSB 8 are data.
      
   3) Using SX/B command:
   
   SHIFTOUT DQ,Clk,MSBFirst,$03  ' to indicate Digit 3
   SHIFTOUT DQ,Clk,MSBFirst,$04  ' to display a 4 
      
Observation:
   1) I observed that LED0 briefly blinks each cycle 
      indicating that SOMETHING is coming OUT of the
      7219 implying that SOMETHING must be going
      INTO the 7219 (I know, wishful thinking).
      
Goal:

   To write a program that will read the DS1307 on 
   the PDB and display the time on the 7 seg displays
   also on the PDB.  SX/B has sample code for doing
   something similar but it runs the LEDs directly
   and uses many pins.  The MAX7219 will only use
   three pins.

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