105 lines
3.0 KiB
C
105 lines
3.0 KiB
C
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/*
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* Code to read in data from two daisychained 74HC165 PISO shift registers.
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*
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* The SN74HC165 is an 8-bit parallel-load shift register that, when clocked,
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* shift the data toward a serial (QH) output. Parallel-in access to each
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* stage is provided by eight individual direct data (A−H) inputs that are
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* enabled by a low level at the shift/load (SH/LD) input. The SN74HC165 also
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* features a clock-inhibit (CLK INH) function and a complementary serial (QH)
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* output.
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*
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* Clocking is accomplished by a low-to-high transition of the clock (CLK)
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* input while SH/LD is held high and CLK INH is held low. The functions of
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* CLK and CLK INH are interchangeable. Since a low CLK and a low-to-high
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* transition of CLK INH also accomplish clocking, CLK INH should be changed
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* to the high level only while CLK is high. Parallel loading is inhibited
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* when SH/LD is held high. While SH/LD is low, the parallel inputs to the
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* register are enabled independently of the levels of the CLK, CLK INH, or
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* serial (SER) input
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*
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* http://www.datasheetcatalog.org/datasheet2/8/0ue9fx650zw5716zs9zch6ks5uwy.pdf
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*
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* To compile and upload run: make clean; make; make program;
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*
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* Copyright 2011 Mika Tuupola
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*
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* Licensed under the MIT license:
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* http://www.opensource.org/licenses/mit-license.php
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*
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*/
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#include <stdlib.h>
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#include <avr/io.h>
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#include <stdio.h>
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#include <util/delay.h>
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#include <stdint.h>
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#include <avr/sfr_defs.h>
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#include "main.h"
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#include "uart.h"
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#include "pins.h"
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#include "digital.h"
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#define LATCH 8 /* sh/ld */
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#define CLOCK 12 /* clk */
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#define DATA 13 /* qh */
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static void init(void) {
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pin_mode(LATCH, OUTPUT);
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pin_mode(CLOCK, OUTPUT);
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pin_mode(DATA, INPUT);
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}
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int shiftin(void) {
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uint8_t byte = 0;
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uint8_t pin_value;
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for(int i=0; i<8; i++) {
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pin_value = digital_read(DATA);
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byte |= (pin_value << ((8 - 1) - i));
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printf("%d = %d \n", ((8 - 1) - i), pin_value);
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/* Pulse clock input (CP) LOW-HIGH to read next bit. */
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digital_write(CLOCK, LOW);
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//_delay_ms(10);
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digital_write(CLOCK, HIGH);
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}
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return byte;
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}
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int main(void) {
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init();
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uart_init();
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stdout = &uart_output;
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stdin = &uart_input;
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uint8_t register_value;
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while (1) {
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/* Read in parallel input by setting SH/LD low. */
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digital_write(LATCH, LOW);
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//_delay_ms(10);
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/* Freeze data by setting SH/LD high. When SH/LD is high data enters */
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/* to reqisters from SER input and shifts one place to the right */
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/* (Q0 -> Q1 -> Q2, etc.) with each positive-going clock transition. */
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digital_write(LATCH, HIGH);
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/* Read in first 74HC165 data. */
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register_value = shiftin();
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printf("%d \n", register_value);
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/* Read in second 74HC165 data. */
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register_value = shiftin();
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printf("%d \n", register_value);
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_delay_ms(2000);
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}
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return 0;
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}
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