replacing crystal with TCXO

Projects General Guidance
20

jboyton:
I think that would work.

I would choose to do something like this:

void DS3234::_read_raw (void)

{
uint8_t x = 7;

digitalWrite (_ss_pin, LOW);
       _spi_transfer(0); // time registers: addr 0-6
while (x--) {
*(_buffer + x) = _spi_transfer(0);
}
       digitalWrite(_ss_pin, HIGH);
}

OK, I tried something: I modified your test sketch to use my library for reads. Sure enough, it's got the problem. Here's the output from the test sketch using the library for read:

[b]

RTC glitch test using DS3234 Library

01:00
00:00
01:00
00:00
00:00
01:00
00:00
00:00
00:00
01:00
00:00
01:00
00:00
[/b]

Now with the define changed to use the software direct read you did:

[b]

RTC glitch test using Burst read

01:00
01:00
01:00
01:00
01:00
01:00
01:00
01:00
01:00
01:00
01:00
01:00[/b]

Here is the test sketch itself if you want to try it:

#include <DS3234.h>

// DS3234 pin connections
#define __GND 99 // solid gnd
#define __VCC 13
#define __SQW 12
#define __SCK 11
#define __MISO 10
#define __MOSI 9
#define __SS 8

// original defines from the test sketch
#define CLK_PIN 11
#define MISO_PIN 10
#define MOSI_PIN 9
#define SS_PIN 8

#define USE_DRIVER // comment this out to use direct read

uint8_t hour, mins, secs, month, day, dow;
uint16_t year;

char buffer[16];

uint8_t bcd2dec (uint8_t bcd)
{
	return (bcd / 16 * 10) + (bcd % 16);
}

void displayMMSS (uint8_t mins, uint8_t secs)
{
	sprintf (buffer, "%02u:%02u\n", mins, secs);
	Serial.print (buffer);
}

// transfer one byte via SPI Mode 3
uint8_t spi_transfer (uint8_t data)
{
	uint8_t bits;
	bits = 8;

	while (bits--) {
		digitalWrite (CLK_PIN, LOW);
		digitalWrite (MOSI_PIN, data & _BV (bits) ? HIGH : LOW);
		digitalWrite (CLK_PIN, HIGH);
		digitalRead (MISO_PIN) ? data |= _BV (bits) : data &= ~_BV (bits);
	}

	return data;
}

uint8_t spi_command (uint8_t cmd, uint8_t data)
{
	digitalWrite (SS_PIN, LOW);
	spi_transfer (cmd);
	cmd = spi_transfer (data);
	digitalWrite (SS_PIN, HIGH);
	return cmd;
}

void burst (uint8_t *secs, uint8_t *mins)
{
	digitalWrite (SS_PIN, LOW);
	spi_transfer (0x00);
	*secs = spi_transfer (0x00);
	*mins = spi_transfer (0x00);
	digitalWrite (SS_PIN, HIGH);
}

int main (void)
{
	init();
	Serial.begin (115200);

	digitalWrite (__GND, LOW);
	digitalWrite (__VCC, HIGH);

	pinMode (__GND, OUTPUT); // enable gnd first
	pinMode (__VCC, OUTPUT); // turn on power for clock
	pinMode (__SQW, INPUT_PULLUP); // no bus contention with SQW pin

	RTC.init (__SCK, __MISO, __MOSI, __SS); // init the RTC

	Serial.print ("\nRTC glitch test using");
#ifdef USE_DRIVER
	Serial.print (" DS3234 Library\n\n");
#else
	Serial.print (" Burst read\n\n");
#endif

	while (1) {
		spi_command (0x80, 0x59); // write seconds = 59
		spi_command (0x81, 0x00); // write minutes = 00

		while (1) {
#ifdef USE_DRIVER
			dow = RTC.getTime (hour, mins, secs, month, day, year);
#else
			burst (&secs, &mins);
			mins = bcd2dec (mins); // raw read is in BCD so convert it
			secs = bcd2dec (secs);
#endif

			if ((secs == 0x00) || (mins == 0x01)) { // if rollover
				displayMMSS (mins, secs);
				break;
			}
		}
	}
}

Lastly, attached is a ZIP file of the DS3234 library. It's been updated a bit from the one on Github, and you should use the same one as I did for testing...

ds3234.zip (4.4 KB)