Understanding & Using the 74HC595 Master Reset Function

1//
2// 74HC595 Programmatic Master Reset
3//
4// Ron Bentley, Stafford   UK
5// February 2022
6//
7// This example and code is in the public domain   and may be used without
8// restriction and without warranty.
9//
10// %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
11//   Example sketch - Demonstration of Programmatic Control of the
12//                  74HC595   Shift Register Master Reset(MR) Function
13// %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
14//
15//   Objective of the sketch
16// ^^^^^^^^^^^^^^^^^^^^^^^
17// To show the operation   of the 74HC595 shift register master reset (MR)
18// function.
19//
20// Approach
21//   ^^^^^^^^
22// To achieve our objective, we need to bring the SIPO IC's master reset   pin
23// (MR, but often labelled SRCLR)under programmatic control.
24// For this,   we allocate a digital microcontroller pin and connect this to the
25// MR (SRCLR)   pin of the SIPO IC.
26//
27// By lowering and raising the signal level of this   pin (LOW/HIGH, 0/+5v)
28// we are able to produce a complete SIPO IC reset as necessary.
29//   To show this operation the sketch uses a simply connected button switch
30// to   toggle the SIPO IC's master reset function and noramal SIPO IC updates.
31//
32//   The sketch uses two libraries:
33// 1. the ez_switch_lib library to define and   control a simply connected
34//    button switch, and
35// 2. the ez_SIPO8_lib   library to define and control a single 74HC595
36//    shift register.
37// These   libraries may be accessed and downloaded via the ARDUINO Project Hub:
38//
39//   1. ez_switch_lib library-
40//    https://create.arduino.cc/projecthub/ronbentley1/a-switch-library-for-arduino-dfbe40?ref=user&ref_id=1455180&offset=17
41//
42//   2. ez_SIPO8_li library-
43//    https://create.arduino.cc/projecthub/ronbentley1/command-control-of-multiple-serial-in-parallel-out-ics-3e0b1a?ref=user&ref_id=1455180&offset=16
44//
45//   If you wish to read a primer for SIPO ICs/shift registers then have a look at the   link below:
46//    https://lastminuteengineers.com/74hc595-shift-register-arduino-tutorial/
47//
48//   ****
49// declare SIPO IC data
50#include <ez_SIPO8_lib.h>
51
52SIPO8 my_SIPOs(1,   0); // configure for one SIPO IC, no timers for this sketch
53
54uint16_t bank_id;
55
56#define   data_pin     8
57#define latch_pin    9
58#define clock_pin   10
59#define IC_MR_pin    11
60
61bool IC_MR_status;
62
63// ****
64// Declare switch data
65#include   <ez_switch_lib.h>
66
67Switches my_switch(1); // establish just one switch for   this sketch
68
69int switch_id;
70
71#define my_switch_pin 12
72
73void setup()   {
74  // ****
75  // Set up switch - a button switch, simply wired without a pulldown   resistor
76  switch_id =
77    my_switch.add_switch(button_switch, my_switch_pin,   circuit_C2); // add & configure the switch
78
79  // ****
80  // Deal with initialisation   of the MR reset pin
81  pinMode(IC_MR_pin, OUTPUT);
82  IC_MR_status = HIGH; //   start with a HIGH signal, ie IC active status, ready for data
83  digitalWrite(IC_MR_pin,   IC_MR_status);
84
85  // ****
86  // Set up the SIPO - one SIPO IC in this bank   on these control pins:
87  bank_id =
88    my_SIPOs.create_bank(data_pin, clock_pin,   latch_pin, 1);
89  // Now set all of the IC's output pins HIGH (LEDs on)
90  my_SIPOs.set_all_array_pins(HIGH);
91   my_SIPOs.xfer_array(MSBFIRST);
92}
93
94void loop() {
95  do {
96    // Only   process if the button switch has been toggled. 
97    // Alternative switch presses   perform direct programmatic IC shift
98    // register master resets and normal   IC updates, respectively
99    if (my_switch.read_switch(switch_id) == switched)   {
100      // Button switch actuated
101      IC_MR_status = !IC_MR_status;    //   invert current IC_MR_status and process
102      if (IC_MR_status == LOW) {
103         // Request to programmatically reset the SIPO IC via the MR pin, so reset   the
104        // IC shift register and ensure output ports also reflect cleared   status by
105        // toggling latch pin
106        digitalWrite(IC_MR_pin, LOW);   // reset IC - drop MR reset pin +5v signal
107        digitalWrite(IC_MR_pin,   HIGH); // set IC back to active status
108        digitalWrite(latch_pin, LOW);   // indicate an update from shift register to output required
109        digitalWrite(latch_pin,   HIGH); // action transfer of register reset state to the outputs
110      } else   {
111        // Normal update the SIPO with all outputs raised HIGH
112        my_SIPOs.set_all_array_pins(HIGH);
113         my_SIPOs.xfer_array(MSBFIRST); // send update to all output ports
114      }
115     }
116  } while (true);
117}
118