Serial to parallel converter 74HC595

published: 17 November 2019 / updated 16 November 2020

Presentation

The symbols are from the Texas Instruments documentation.

PIN	SYMBOL	DESCRIPTION
1	Q1	parallel data output
2	Q2	parallel data output
3	Q3	parallel data output
4	Q4	parallel data output
5	Q5	parallel data output
6	Q6	parallel data output
7	Q7	parallel data output
8	GND	ground (0 V)
9	Q7	parallel data output
10	SRCLR	master reset (active LOW)
11	SRCLK	Shift Register CLocK input
12	RCLK	Register CLocK input
13	OE	output enable (active LOW)
14	SER	SERial data input
15	Q0	parallel data output
16	VCC	positive supply voltage

Connecting the 74HC595 converter

In order not to overload the ARDUINO board, the converter is powered by a source external, here in red on the prototyping board.

connecting the 74HC595 to the ARDUINO MEGA board

pin	vers - to
10	SRCLR -> external +5V
11	SRCLK -> PB6 - pin 12 ARDUINO MEGA
12	RCLK -> PB5 - pin 11 ARDUINO MEGA
13	OE -> external GND
14	SER -> PB4 - pin 10 ARDUINO MEGA
16	VCC -> external +5V

Serial to parallel conversion

We define in advance the PORTB:

\ for more 1 74HC595, change 1 by number of HC595 
1 constant NB_74HC595 
NB_74HC595 8 * constant NB_REG_PINS \ number of Register Pins 
 
\ PORTB 
37 constant PORTB	\ Port B Data Register 
36 constant DDRB	\ Port B Data Direction Register 
\ 35 constant PINB	\ Port B Input Pins - unused

The words defPIN: high low output input and pin@ are described in the article Definition and management of PORT connections

With defPIN: we create the words SER RCLK SRCLK. These words designates connectors of the ARDUINO cate and are named according to their use in relation with the 74HC595 converter:

\ for Arduino MEGA 
PORTB %00010000 defPIN: SER     \ PB4 -> pin 14 on the 74HC595 - dataPin 
PORTB %00100000 defPIN: RCLK    \ PB5 -> pin 12 on the 74HC595 - latchPin 
PORTB %01000000 defPIN: SRCLK   \ PB6 -> pin 11 on the 74HC595 - clockPin 
\ PORTB %10000000 defPIN: OE      \ PB7 -> pin 13 on the 74HC595

The word init.74HC595 initializes the bits of the PORTB designated by SER RCLK SRCLK as outputs and set these bits low.

: init.74HC595 ( ---) 
    SER     output 
    RCLK    output 
    SRCLK   output 
    SER     low 
    RCLK    low 
    SRCLK   low 
  ;

The word csend sends a byte to the 74HC595 converter. The word csend provides serialization of the bit byte:

: csend ( c ---) 
    RCLK low                    \ latchPin LOW 
    NB_REG_PINS 
    for 
        dup $80 and 
        if      SER high        \ datapin HIGH 
        else    SER low         \ datapin LOW 
        then 
        1 lshift 
        SRCLK high              \ clockPin HIGH 
        SRCLK low               \ clockPin LOW 
    next 
    drop     
    RCLK high                   \ latchPin HIGH 
  ;

Complete source code

The complete listing is available here: 8 bit data in serial and send it to 74HC595 chip