SPI hardware communication issue

Hello,

Can I have some guidance, I have written the code below to drive a set of LEDs attached to a SN74HC595, I am using a PIC16F1825 to drive the SN74HC595.

3 LEDs are attached to the PIC16F1825 to provide feedback that the code is cycling as expected. These all function correctly.

The connection between the PIC and the shift register is as below:

PIC16F1825 SN74HC595
SDO PIN 3 RA4 PIN 14 SER
SDI PIN 9 RA5 Floating Not Connected
SCK PIN 10 RC0 PIN 11 SRCLK
Latch out PIN 11 RA2 PIN 12 RCLK

Common ground and 5V power supply is provided to both the PIC and shift register. no resistors or capacitors are connected between the PIC and the shift register.

LEDs are connected to the 9 outputs of the shift register.

The LEDs attached to the shift register stay lit, but do not cycle off, or make any of the expected patterns.

What am I doing wrong? Thank you in advance.

Code:

TxData var BYTE define OSC 4 OSCCON = %01101010 HC_Data var PORTA.4 'SDO HC_Clk var PORTC.0 'SCK HC_latch var PORTA.2 'Digital output LED_YELLOW var PORTA.1 LED_GREEN var PORTC.3 LED_RED var PORTA.0 TRISA = 0 'all digital outputs PORTA = 0 'make all pins low ANSELA = 0 TRISC = %00000010 'all digital outputs except port 1 PORTC = 0 'make all pins low ANSELC = 0 APFCON0 = %01000000 'set SPI pin alternative SSP1STAT = %00000000 SSP1CON1 = %01100010 SSP1CON3 = %00010000 txdata = 0 'SPI output byte pause 200 'prove LED function LED_YEllow = 1 LED_Green = 1 LED_red = 1 pause 200 LED_YEllow = 0 LED_Green = 0 LED_red = 0 Main: 'set up sequence of signals for output LED_Yellow = 1 TxData = %10101010 Gosub Send_Data TXDATA = %00000000 Gosub Send_Data TxData = %10000000 Gosub Send_Data TxData = %01000000 Gosub Send_Data TxData = %00100000 Gosub Send_Data LED_Yellow = 0 LED_gREEN = 1 TxData = %00010000 Gosub Send_Data TxData = %00001000 Gosub Send_Data TxData = %00000100 Gosub Send_Data TXDATA = %00000010 Gosub Send_Data TXDATA = %00000001 Gosub Send_Data LED_GREEN = 0 goto main end Send_Data : SSP1CON1.5 = 0 SSP1CON1.5 = 1 toggle LED_RED PAUSEUS 10 SSP1BUF = TXDATA PAUSEUS 10 HC_Latch=1 pauseus 5 HC_Latch=0 pause 750 return

Re: SPI hardware communication issue

I don't think you have set the mssp port correctly and

Quote:

PAUSEUS 10
SSP1BUF = TXDATA
PAUSEUS 10

is a dangerous way to wait for tx to complete before latching data

try this , it works perfectly for me

Code:

'**************************************************************** '* Name : SPI_74HC595.BAS * '* Author : RICHARD * '* Notice : * '* : * '* Date : 2/26/2018 * '* Version : 1.0 * '* Notes : * '* : * '**************************************************************** #CONFIG __config _CONFIG1, _FOSC_INTOSC & _CP_OFF & _WDTE_OFF & _PWRTE_ON & _MCLRE_ON & _CLKOUTEN_OFF __config _CONFIG2, _PLLEN_OFF & _LVP_OFF #ENDCONFIG TxData var BYTE define OSC 4 OSCCON = %01101010 HC_Data var PORTA.4 'SDO HC_Clk var PORTC.0 'SCK HC_latch var LATA.2 'Digital output LED_RED var LATA.1 TRISA = %11101001 PORTA = 0 'make all pins low ANSELA = 0 TRISC = %11111110 'digital output C.0 PORTC = 0 'make all pins low ANSELC = 0 APFCON0 = %01000000 'set SPI pin alternative SSP1CON1=$22 SSP1STAT=$40 pause 200 'prove LED function LED_red = 1 pause 200 LED_red = 0 Main: 'set up sequence of signals for output TxData = 0 Gosub Send_Data TXDATA = 1 Gosub Send_Data TxData = 2 Gosub Send_Data TxData = 4 Gosub Send_Data TxData = 15 Gosub Send_Data goto main end Send_Data : LED_RED=!LED_RED pir1.3=0 SSP1BUF = TXDATA while ! pir1.3 :wend ;WAIT TILL TX COMPLETES HC_Latch=0 ;LATCH IN NEW DATA ;@ NOP ; IF NEEDED FOR HIGHER CLOCK SPEEDS HC_Latch=1 pause 500 return

Re: SPI hardware communication issue

Hi Richard,

Thank you for the response, and thank you for the working example.

I shall review it tomorrow after work.

Just for reference what PIC did you use with that code?

Many thanks.

Re: SPI hardware communication issue

same as you 16f1825

Re: SPI hardware communication issue

I uploaded that code before work and can confirm it worked perfectly, now to study it when I get home and understand where my mistakes are in my original code.

Thank you for your help.

Re: SPI hardware communication issue

My thanks goes to Richard for his help. But as a benefit to anybody else struggling with this, my corrections to my code are as follows:

I can confirm that CLKOUT configuration line was the largest issue, as this was blocking the output of the SDO1 therefore the signal to the SN74HC595 was not being sent.

I have taken Richard's advice to implement using the interrupt flag to check when the signal had been sent to the SN74HC595, though the my next step is to have this trigger as interrupt to control the latch while performing another routine.

Finally changed the clock edge bit such that the signal is sent on the correct edge of the clock signal for the serial data output so the data arrives at the SN74HC595 correctly.

This is my modified code based on my initial code:

Code:

#CONFIG __config _CONFIG1, _CLKOUTEN_OFF #ENDCONFIG TxData var BYTE define OSC 4 OSCCON = %01101010 HC_Data var PORTA.4 'SDO HC_Clk var PORTC.0 'SCK HC_latch var PORTA.2 'Digital output LED_YELLOW var PORTA.1 LED_GREEN var PORTC.3 LED_RED var PORTA.0 SSP1IF VAR PIR1.3 'SPI interrupt flag TRISA = 0 'all digital outputs PORTA = 0 'make all pins low ANSELA = 0 TRISC = %00000010 'all digital outputs except port 1 PORTC = 0 'make all pins low ANSELC = 0 APFCON0 = %01000000 'set SPI pin alternative SSP1STAT = %01000000 SSP1CON1 = %00100010 'prove LED function LED_YEllow = 1 LED_Green = 1 LED_red = 1 pause 200 LED_YEllow = 0 LED_Green = 0 LED_red = 0 Main: 'set up sequence of signals for output LED_Yellow = 1 TXDATA = %00000000 Gosub Send_Data TxData = %10101010 Gosub Send_Data TxData = %01010101 Gosub Send_Data TXDATA = %00000000 Gosub Send_Data TxData = %10000000 Gosub Send_Data TxData = %01000000 Gosub Send_Data TxData = %00100000 Gosub Send_Data LED_Yellow = 0 LED_gREEN = 1 TxData = %00010000 Gosub Send_Data TxData = %00001000 Gosub Send_Data TxData = %00000100 Gosub Send_Data TXDATA = %00000010 Gosub Send_Data TXDATA = %00000001 Gosub Send_Data TXDATA = %11111111 Gosub Send_Data LED_GREEN = 0 goto main end Send_Data : toggle LED_RED SSP1IF = 0 SSP1BUF = TXDATA while ! SSP1IF :wend ;WAIT TILL TX COMPLETES HC_Latch=1 'could need a delay here on high processor speeds or no operation commands HC_Latch=0 pause 500 return

Re: SPI hardware communication issue

Quote:

though the my next step is to have this trigger as interrupt to control the latch while performing another routine

It might be a lot less complicated to just increase the osc speed from 4MHz and clock the SPI faster. Running at 32MHz with SPICLK=8MHz it takes <2us to send out a byte... hardly worth the bother. At the speed you're running now it takes longer than that just to branch to an interrupt.

I'd also ditch the PAUSE in the Send_Data routine.