DS3231RTC notes

By tlfong01 on February 7, 2023 • ( Leave a comment )

pico pi rtc interrupt

Asked 1 year, 5 months ago

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I want to send an interrupt to the pico to wake it up every second to tick a battery powered clock. I have an external RTC, the ds3231. i have gotten just about every other feature on the rtc to work like the time keeping, time setting, format etc. But I cannot get the SQW pin to pulse at 1hz. it is just high all the time. I made sure to have a pulldown resistor, but it always reads high.

the adafruit library here does not have anything for the square wave. but it does have an alarm. maybe that can be useful but I don’t know.

The library by Peter Hinch here has a similar issue for the ds3231.

Aa random new library for the ds3231 here actually claims to support the square wave feature, but it just stays on. I am aware that the alarms disable the sqw, so I do not have them enabled.

Perhaps I could use the internal rtc in the pico. If anyone can help me it would be appreciated

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edited 22 hours ago

Rohit Gupta

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asked Aug 16, 2021 at 5:23

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Question

How to configure a DS3231 RTC (Real Time Clock) to output an interrupt signal, once every second, to wake up a Rpi Pico/W?

Answer

DS3231 alarm Interrupt 1Hz (Appendix L)

DS3231 Sq Wve 1 Hz (Appendix J)

Troubleshooting notes on pull-up/pull down resistors

The OP says the following:

“But I cannot get the SQW pin to pulse at 1hz. it is just high all the time. I made sure to have a pulldown resistor, but it always reads high.”

Actually if the OP is using a assembled module like mine, then he does not need to use any pull up resistor, because there is already a 4k7 pull-up built in. So if he uses a pull-down resistor, the the Sq/INI pin with both a pull up and pull down resistor will form a potentiometer divider with a constant voltage output.

/ to continue, …

References

(1) DS3231 Real Time Clock Datasheet – Maxim Integrated 2015

(2) DS3231 Real Time Clock Module – AliExpress HK$14

(3) GitHub Adafruit_CircuitPython_DS3231 Library (OP Ref 1)

(4) GitHub PeterHinch micropython-samples DT3231 Library (OP Ref 2)

(5) GitHub Micropython-DS3231-AT24C32 Library – pangopi (OP Ref 3)

(6) MicroPython time related function – MicroPython Library

(7) Rpi Pico MicroPython Delay and timing

/ to continue, …

Appendices

(A) DS3231 Wiring Diagram

(B) DS3231 Block Diagram

(D) DS3231 Interrupt/Square wave pin description

(E) DS3231 Alarm 1 setting (for interrupt once every second)

(F) Control Register (0x0E) Setting for interrupt once per second

(G) DS3231 Wiring Scheme

(H) DS3231 on I2C1 detected OK (0x68 = DS3231, 0x53 = EEPROM)

# *** Print title ***

print('*** Program =', 'DS3231 Test v0.8 tlfong01 2023feb04hkt1211 ***')

# ***  Contents ***

# 1. References
# 2. Import modules
# 3. Scan I2C1 Devices - tested OK

# 2.  *** Import modules ***

import machine

# ========= ========= ========= ========= ========= ========= ========= =========  

# 3.  *** Scan I2C devices ***

# *** Create I2C object for I2C bus # 1 Freq 100 kHz ***

i2c1 = machine.I2C(1, scl = machine.Pin(7), sda = machine.Pin(6), freq = 100000)

# *** Function to scan I2C devices ***

def scanI2c(i2c):
    devAddrList = i2c.scan()
    return devAddrList

# *** Sample test and ouput ***

def scanPrintI2cDevices(i2c):
    devAddrList = scanI2c(i2c)
    print('Scan I2C devices =', end = '')
    for devAddr in devAddrList:
        print(' ', hex(devAddr), end = '')
    print('')
    return

# *** Sample test and output ***

# *** Sample Test ***
scanPrintI2cDevices(i2c1)

'''
# *** Sample output ***
>>> %Run -c $EDITOR_CONTENT
*** Program = DS3231 Test v0.8 tlfong01 2023feb04hkt1211 ***
Scan I2C devices =  0x57  0x68
*** End of Program ***
>>> 
'''

print('*** End of Program ***')

# *** End of program ***

(I) How to reset interrupt using 0x0f register

(J) Interrupt signal per second using 1 Hz Square wave clock

# *** Print title ***

print('*** Program =', 'DS3231 Test feb0601 tlfong01 2023feb06hkt1458 ***')

# ***  Contents ***

# 1. Import modules
# 2. Scan I2C1 Devices - tested OK
# 3. Functions
#      3.1 read/write device registers
#      3.2 setup alarm register list
#

# 2.  *** Import modules ***

import machine

# ========= ========= ========= ========= ========= ========= ========= =========  

# 3.  *** Scan I2C devices ***

# *** Create I2C object for I2C bus # 1 Freq 100 kHz ***

i2c1 = machine.I2C(1, scl = machine.Pin(7), sda = machine.Pin(6), freq = 100000)

# *** Function to scan I2C devices ***

def scanI2c(i2c):
    devAddrList = i2c.scan()
    return devAddrList

# *** Sample test and ouput ***

def scanPrintI2cDevices(i2c):
    devAddrList = scanI2c(i2c)
    print('  I2C devices scanned =', end = '')
    for devAddr in devAddrList:
        print(' ', hex(devAddr), end = '')
    print('')
    return

# *** Sample test and output ***

# *** Sample Test ***
scanPrintI2cDevices(i2c1)

'''
# *** Sample output ***
>>> %Run -c $EDITOR_CONTENT
*** Program = DS3231 Test v0.8 tlfong01 2023feb04hkt1211 ***
Scan I2C devices =  0x57  0x68
*** End of Program ***
>>> 
'''

# ========= ========= ========= ========= ========= ========= ========= ========= 

# *** Read/Write I2C device registers ***

def writeRegByte(i2cBus, i2cDevAddr, regNum, writeByte):
    writeByteArray = bytearray()
    writeByteArray.append(writeByte)
    i2cBus.writeto_mem(i2cDevAddr, regNum, writeByteArray)
    return

def ds3231WriteRegByte(regNum, writeByte):
    writeRegByte(i2c1, 0x68, regNum, writeByte)
    return
    
def readRegByte(i2cBus, i2cDevAddr, regNum):
    readByte = i2cBus.readfrom_mem(i2cDevAddr, regNum, 1)
    return readByte

def ds3231ReadRegByte(regNum):
    readByte = i2c1.readfrom_mem(0x68, regNum, 1)
    return readByte

# *** Configuration ***

# *** Control and Status Registers ***

ctrlRegNum       = 0x0e
statusRegNum     = 0x0f

# *** Alarm 1 registers and control bit/byte ***

alarm1SecRegNum  = 0x07
alarm1MinRegNum  = 0x08
alarm1HrRegNum   = 0x09
alarm1DyDtRegNum = 0x0a
alarm1RegTotal    = 4
alarm1RegList     = [alarm1SecRegNum, alarm1MinRegNum, alarm1HrRegNum, alarm1DyDtRegNum]

bit7SetByte            = 0x80
alarm1RegInt1SecByteList = [bit7SetByte, bit7SetByte, bit7SetByte, bit7SetByte]

def setupAlarm1RegList(alarm1RegCtrlByteList):
    for i in range(alarm1RegTotal):
        ds3231WriteRegByte(alarm1RegList[i], alarm1RegCtrlByteList[i])        
    return

# *** Test setup alarm 1 reg list and sample output ***
setupAlarm1RegList(alarm1RegInt1SecByteList)
print('  alarm 1 reg list contents = ', end = '')
for alarmReg in alarm1RegList:
    print(ds3231ReadRegByte(alarmReg), end = '')

# ========= ========= ========= ========= ========= ========= ========= ========= 

# *** Alarm 2 registers and control bit/byte ***

alarm2SecRegNum  = 0x0b
alarm2MinRegNum  = 0x0c
alarm2HrRegNum   = 0x0d
alarm2RegTotal    = 3
alarm2RegList     = [alarm2SecRegNum, alarm2MinRegNum, alarm2HrRegNum]

bit7SetByte            = 0x80
alarm2RegInt1SecByteList = [bit7SetByte, bit7SetByte, bit7SetByte]

def setupAlarm2RegList(alarm2RegCtrlByteList):
    for i in range(alarm2RegTotal):
        ds3231WriteRegByte(alarm2RegList[i], alarm2RegCtrlByteList[i])        
    return

# *** Test setup alarm 2 reg list and sample output ***
setupAlarm2RegList(alarm2RegInt1SecByteList)
print('')
print('  alarm 2 reg list contents = ', end = '')
for alarmReg in alarm2RegList:
    print(ds3231ReadRegByte(alarmReg), end = '')

# ========= ========= ========= ========= ========= ========= ========= =========

# *** Setup Control registers ***
CtrlByteBase           = 0x00
CtrlRegOscEnbl         = 0x01 << 7 # ~EOSC
CtrlRegIntCtrl         = 0x01 << 2 # INTCN
CtrlRegAlm1IntEnbl     = 0x01 << 0 # AIIE

#Int1HzCnfgByte   = 0x00 | (~CtrlRegOscEnbl) |  CtrlRegIntCtrl  | CtrlRegAlm1IntEnbl # 0x05
#SqWveCnfgByte    = 0x00 | (~CtrlRegOscEnbl) | (~CtrlRegIntCtrl)  | CtrlRegAlm1IntEnbl # 0x01

int1SecCnfgByte      = 0x05 
int1MinCnfgByte      = 0x06

sqWveCnfgByte1Hz     = 0x01 
sqWveCnfgByte1kHz    = 0x19 

# *** Setup Ctrl Reg 0x0e with ctrl byte 0x05 ***
print('')
print('  int1SecCnfgByte   = ', hex(int1SecCnfgByte))
print('  int1MinCnfgByte   = ', hex(int1MinCnfgByte))
print('  sqWveCnfgByte1Hz  = ', hex(sqWveCnfgByte1Hz))
print('  sqWveCnfgByte1kHz = ', hex(sqWveCnfgByte1kHz))

# *** Config Int 1 sec/1min, Square Wave 1Hz/1kHz ***
ds3231WriteRegByte(ctrlRegNum, sqWveCnfgByte1Hz)
#ds3231WriteRegByte(ctrlRegNum, sqWveCnfgByte1kHz)

#ds3231WriteRegByte(ctrlRegNum, int1SecCnfgByte)
#ds3231WriteRegByte(ctrlRegNum, int1MinCnfgByte)

readByte = ds3231ReadRegByte(ctrlRegNum)
print('  readByte from ctrlReg =', readByte)

# ========= ========= ========= ========= ========= ========= ========= =========

# *** Read status rgister / reset interrupt flass / Enable/Disable clock 32 kHz signal ***

statusByteBase         = 0x00
clock32kHzEnbl         = 0x01 << 3
alarm2FlagReset        = 0x01 << 1
alarm1FlagReset        = 0x01 << 0

resetAlarmsByte        = statusByteBase | alarm1FlagReset | alarm2FlagReset | clock32kHzEnbl # 0x0b

ds3231WriteRegByte(statusRegNum, resetAlarmsByte)

readByte = ds3231ReadRegByte(statusRegNum)
print('  readByte from statusReg =', readByte)

# ========= ========= ========= ========= ========= ========= ========= =========

print('*** End of Program ***')

'''
Sample output 2023jun06hkt1603

*** Program = DS3231 Test feb0601 tlfong01 2023feb06hkt1458 ***
  I2C devices scanned =  0x57  0x68
  alarm 1 reg list contents = b'\x80'b'\x80'b'\x80'b'\x80'
  alarm 2 reg list contents = b'\x80'b'\x80'b'\x80'
  int1SecCnfgByte   =  0x5
  int1MinCnfgByte   =  0x6
  sqWveCnfgByte1Hz  =  0x1
  sqWveCnfgByte1kHz =  0x19
  readByte from ctrlReg = b'\x01'
  readByte from statusReg = b'\x0b'
*** End of Program ***
'''

(K) The OP wishwes to know the feasibility of using Rpi Pico’s internal RTC, instead of the external RTC 3231. Actually Pico does not have any internal RTC. though it has (a) MicoPython delay function, (b) systems timers, as summaried below:

Using the MicroPython time module

import time

time.sleep(1) # sleep for 1 second time.sleep_ms(500) # sleep for 500 milliseconds time.sleep_us(10) # sleep for 10 microseconds start = time.ticks_ms() # get millisecond counter delta = time.ticks_diff(time.ticks_ms(), start) # compute time difference

Using Rpi Pico Timers

RP2040’s system timer peripheral provides a global microsecond timebase and generates interrupts for it. The software timer is available currently, and there are unlimited number of them (memory permitting). There is no need to specify the timer id (id=-1 is supported at the moment) as it will default to this.

Use the machine.Timer class:

from machine import Timer

tim = Timer(period=5000, mode=Timer.ONE_SHOT, callback = lambda t:print(1))

(L) Generate Alarm Interrupt every timer

The following program generate alarm interrupt every second. The while loop as the end of the program is to check if there is another alarm interrupt, and if yes, the interrupt flap at the status register 0x0f is executed to immediately clear the interrupt flag. Note – If there is no interrupt flag reset every time interrupt is detected, the scope will display just a zero volt/ground line.

# *** Print title ***

print('*** Program =', 'DS3231 Test feb0601 tlfong01 2023feb07hkt2151 ***')

# ***  Contents ***

# 1. Import modules
# 2. Scan I2C1 Devices - tested OK
# 3. Functions
#      3.1 read/write device registers
#      3.2 setup alarm register list
#

# 2.  *** Import modules ***

import machine
import time

# ========= ========= ========= ========= ========= ========= ========= =========  

# 3.  *** Scan I2C devices ***

# *** Create I2C object for I2C bus # 1 Freq 100 kHz ***

i2c1 = machine.I2C(1, scl = machine.Pin(7), sda = machine.Pin(6), freq = 100000)

# *** Function to scan I2C devices ***

def scanI2c(i2c):
    devAddrList = i2c.scan()
    return devAddrList

# *** Sample test and ouput ***

def scanPrintI2cDevices(i2c):
    devAddrList = scanI2c(i2c)
    print('  I2C devices scanned =', end = '')
    for devAddr in devAddrList:
        print(' ', hex(devAddr), end = '')
    print('')
    return

# *** Sample test and output ***

# *** Sample Test ***
scanPrintI2cDevices(i2c1)

'''
# *** Sample output ***
>>> %Run -c $EDITOR_CONTENT
*** Program = DS3231 Test v0.8 tlfong01 2023feb04hkt1211 ***
Scan I2C devices =  0x57  0x68
*** End of Program ***
>>> 
'''

# ========= ========= ========= ========= ========= ========= ========= ========= 

# *** Read/Write I2C device registers ***

def writeRegByte(i2cBus, i2cDevAddr, regNum, writeByte):
    writeByteArray = bytearray()
    writeByteArray.append(writeByte)
    i2cBus.writeto_mem(i2cDevAddr, regNum, writeByteArray)
    return

def ds3231WriteRegByte(regNum, writeByte):
    writeRegByte(i2c1, 0x68, regNum, writeByte)
    return
    
def readRegByte(i2cBus, i2cDevAddr, regNum):
    readByte = i2cBus.readfrom_mem(i2cDevAddr, regNum, 1)
    return readByte

def ds3231ReadRegByte(regNum):
    readByte = i2c1.readfrom_mem(0x68, regNum, 1)
    return readByte

# *** Configuration ***

# *** Control and Status Registers ***

ctrlRegNum       = 0x0e
statusRegNum     = 0x0f

# *** Alarm 1 registers and control bit/byte ***

alarm1SecRegNum  = 0x07
alarm1MinRegNum  = 0x08
alarm1HrRegNum   = 0x09
alarm1DyDtRegNum = 0x0a
alarm1RegTotal    = 4
alarm1RegList     = [alarm1SecRegNum, alarm1MinRegNum, alarm1HrRegNum, alarm1DyDtRegNum]

bit7SetByte            = 0x80
alarm1RegInt1SecByteList = [bit7SetByte, bit7SetByte, bit7SetByte, bit7SetByte]

def setupAlarm1RegList(alarm1RegCtrlByteList):
    for i in range(alarm1RegTotal):
        ds3231WriteRegByte(alarm1RegList[i], alarm1RegCtrlByteList[i])        
    return

# *** Test setup alarm 1 reg list and sample output ***
setupAlarm1RegList(alarm1RegInt1SecByteList)
print('  alarm 1 reg list contents = ', end = '')
for alarmReg in alarm1RegList:
    print(ds3231ReadRegByte(alarmReg), end = '')

# ========= ========= ========= ========= ========= ========= ========= ========= 

# *** Alarm 2 registers and control bit/byte ***

alarm2SecRegNum  = 0x0b
alarm2MinRegNum  = 0x0c
alarm2HrRegNum   = 0x0d
alarm2RegTotal    = 3
alarm2RegList     = [alarm2SecRegNum, alarm2MinRegNum, alarm2HrRegNum]

bit7SetByte            = 0x80
alarm2RegInt1SecByteList = [bit7SetByte, bit7SetByte, bit7SetByte]

def setupAlarm2RegList(alarm2RegCtrlByteList):
    for i in range(alarm2RegTotal):
        ds3231WriteRegByte(alarm2RegList[i], alarm2RegCtrlByteList[i])        
    return

# *** Test setup alarm 2 reg list and sample output ***
setupAlarm2RegList(alarm2RegInt1SecByteList)
print('')
print('  alarm 2 reg list contents = ', end = '')
for alarmReg in alarm2RegList:
    print(ds3231ReadRegByte(alarmReg), end = '')

# ========= ========= ========= ========= ========= ========= ========= =========

# *** Setup Control registers ***
CtrlByteBase           = 0x00
CtrlRegOscEnbl         = 0x01 << 7 # ~EOSC
CtrlRegIntCtrl         = 0x01 << 2 # INTCN
CtrlRegAlm1IntEnbl     = 0x01 << 0 # AIIE

#Int1HzCnfgByte   = 0x00 | (~CtrlRegOscEnbl) |  CtrlRegIntCtrl  | CtrlRegAlm1IntEnbl # 0x05
#SqWveCnfgByte    = 0x00 | (~CtrlRegOscEnbl) | (~CtrlRegIntCtrl)  | CtrlRegAlm1IntEnbl # 0x01

int1SecCnfgByte      = 0x05 
int1MinCnfgByte      = 0x06

sqWveCnfgByte1Hz     = 0x01 
sqWveCnfgByte1kHz    = 0x19 

# *** Setup Ctrl Reg 0x0e with ctrl byte 0x05 ***
print('')
print('  int1SecCnfgByte   = ', hex(int1SecCnfgByte))
print('  int1MinCnfgByte   = ', hex(int1MinCnfgByte))
print('  sqWveCnfgByte1Hz  = ', hex(sqWveCnfgByte1Hz))
print('  sqWveCnfgByte1kHz = ', hex(sqWveCnfgByte1kHz))

# *** Config Int 1 sec/1min, Square Wave 1Hz/1kHz ***

#ds3231WriteRegByte(ctrlRegNum, sqWveCnfgByte1Hz)
#ds3231WriteRegByte(ctrlRegNum, sqWveCnfgByte1kHz)

#ds3231WriteRegByte(ctrlRegNum, int1SecCnfgByte)
ds3231WriteRegByte(ctrlRegNum, int1MinCnfgByte)

readByte = ds3231ReadRegByte(ctrlRegNum)
print('  readByte from ctrlReg =', readByte)

# ========= ========= ========= ========= ========= ========= ========= =========

# *** Read status rgister / reset interrupt flass / Enable/Disable clock 32 kHz signal ***

statusByteBase         = 0x00

#clock32kHzEnbl         = 0x01 << 3
#alarm2FlagReset        = 0x01 << 1
#alarm1FlagReset        = 0x01 << 0
#resetAlarmsByte        = statusByteBase | alarm1FlagReset | alarm2FlagReset | clock32kHzEnbl # 0x00
#ds3231WriteRegByte(statusRegNum, resetAlarmsByte)
resetAlarmByte = 0x00

# *** Generate interrupt every second ***
print('  Generate interrupt every second')
ds3231WriteRegByte(ctrlRegNum, int1SecCnfgByte) #generate interrupt every second

# *** Reset interrupt flag every 50mS ***
while True:
    ds3231WriteRegByte(statusRegNum, resetAlarmByte)
    time.sleep_ms(50)
    
# ========= ========= ========= ========= ========= ========= ========= =========

print('*** End of Program ***')

# *** End of program ***

'''
Sample Output
>>> %Run -c $EDITOR_CONTENT
*** Program = DS3231 Test feb0601 tlfong01 2023feb07hkt2151 ***
  I2C devices scanned =  0x57  0x68
  alarm 1 reg list contents = b'\x80'b'\x80'b'\x80'b'\x80'
  alarm 2 reg list contents = b'\x80'b'\x80'b'\x80'
  int1SecCnfgByte   =  0x5
  int1MinCnfgByte   =  0x6
  sqWveCnfgByte1Hz  =  0x1
  sqWveCnfgByte1kHz =  0x19
  readByte from ctrlReg = b'\x06'
  Generate interrupt every second
'''

.END

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edited 4 mins ago

answered Feb 3 at 12:15

tlfong01

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Disclaimer: I’m not sure I understand your question, and your objective doesn’t make sense to me. Consequently, this is probably not really an answer, but too long for a comment, so here goes:

I’ve zero experience with the Pico Pi, and not much more with Python. I know a little bit about the DS3231 – so perhaps this will be helpful. If you’ve not read the DS3231 data sheet, that may shed some light. This passage from the data sheet describes the functional logic of the INT/SQW pin:

Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor connected to a supply at 5.5V or less. This multifunction pin is determined by the state of the INTCN bit in the Control Register (0Eh). When INTCN is set to logic 0, this pin outputs a square wave and its frequency is determined by RS2 and RS1 bits. When INTCN is set to logic 1, then a match between the timekeeping registers and either of the alarm registers activates the INT/SQW pin (if the alarm is enabled). Because the INTCN bit is set to logic 1 when power is first applied, the pin defaults to an interrupt output with alarms disabled. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC. If not used, this pin can be left unconnected.

Here’s how I understand this wrt your question:

The INTCN bit controls whether pin 3 (INT/SQW) outputs an INTerrupt, or a SQuareWave.
If INTCN is set to 0, a square wave is output
The default value for INTCN is 1; set at power-on

Consequently, you must use the i2c bus to set INTCN to 0. Please note that this seems to be a necessary condition, but it is not a sufficient condition. I don’t understand why setting the INTCN bit would be a huge problem for someone who has gone to the trouble of creating a DS3231 library – but that may be harsh because I’ve never written such a library.

In closing, please forgive this interruption if it’s something you already knew, or if it is useless information. Please let me know if that’s the case as I’d like to delete this answer if it misses the mark.

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edited Feb 12, 2022 at 23:44

answered Feb 12, 2022 at 0:16

Seamus

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