SPI hardware communication issue

[Lestat]

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.

[richard]

same as you 16f1825

[Lestat]

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.

[Lestat]

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:

#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

[tumbleweed]

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.