PSoC5LP Lab 09: I2C RTC Module

Ensure the DS3231 oscillator is enabled and verify that the date/time values are valid before use.

Registers of Interest

• 0x0E – Control Register
  • Bit 7 (EOSC): Enable Oscillator (0 = oscillator enabled, 1 = disabled).
• 0x0F – Status Register
  • Bit 7 (OSF): Oscillator Stop Flag (1 = oscillator stopped; date/time unreliable, 0 = normal operation).

Steps

1. Enable Oscillator
   • Read the Control register (0x0E).
   • Ensure bit 7 (/EOSC) is cleared (0). If set, clear it to enable the oscillator.
2. Check Oscillator Stop Flag
   • Read the Status register (0x0F).
   • If bit 7 (OSF) = 1, it means the RTC oscillator has stopped (e.g., due to power loss or first-time use).
   • In this case:
     • Display a message on the LCD, such as:
         
     • Prevent normal operation until the user updates the RTC with a valid date/time via Exercise 2.
3. Clear OSF After Update
   • Once a valid date/time is written to the RTC, clear the OSF bit by writing 0 to it.

Read the current date and time from the DS3231 RTC via I2C, decode the raw BCD-encoded register values, and display the information on the LCD in 12-hour format with AM/PM, refreshing once per second.

DS3231 RTC I2C Register Reference (00x00 ~ 0x06)

Key Concepts

• Year Handling:
  • The RTC stores only two-digit years (00 ~ 99).
  • Use the Month register bit 7 (Century bit) to distinguish centuries:
    • 0 = 19xx or 20xx (implementation-defined, typically 20xx).
    • 1 = +100 years (e.g., 2100–2199).
  • For this lab, assume all years are 20xx (e.g., 0x25 → 25 → 2025).
• BCD Conversion:
  • Each field is stored in BCD (binary-coded decimal). Example: 0x25 = 25.
  • Create Macro Functions:

    #define DEC2BCD(dec) (________)
    #define BCD2DEC(bcd) (________)

• Day-of-Week Mapping:
  • Values 1 ~ 7 (not zero-based).
  • Map to labels: 1 = SU, 2 = MO, 3 = TU, 4 = WE, 5 = TH, 6 = FR, 7 = SA.
• Hours Format:
  • The RTC can be in either 12-hour or 24-hour mode.
  • For this lab, always display in 12-hour format with AM/PM.
  • Bit 6 of the Hours register:
    • 0 = 24-hour format (bits 5 ~ 4 hold 20h digit).
    • 1 = 12-hour format; then Bit 5 = AM/PM flag (0 = AM, 1 = PM).

Steps

1. Read RTC registers 0x00 ~ 0x06 via I2C in one burst read.
2. Convert BCD values into decimal for seconds, minutes, hours, days, dates, months, and years.
   
3. Process Hours:
   • If RTC is in 24-hour mode (bit 6 = 0): convert BCD hours (00–23) into decimal, then convert to 12-hour format in software:
   • If RTC is in 12-hour mode (bit 6 = 1), extract hours and use Bit 5 to determine AM/PM.
4. Reconstruct the full year:
   • Two-digit year + assumed century.
   • Example: Year=0x25 → 25, Century=0 → 2025.
5. Display on LCD in 12-hour format with AM/PM every second:
     

Hits

1. I2C Access:
   • Use the I2C Master APIs in PSoC Creator to read multiple bytes starting from register 0x00.
   • The DS3231 stores time/date across 7 registers (0x00 ~ 0x06).
2. BCD Conversion:
   • Always convert before displaying.
   • Example: 0x25 (BCD) → decimal 25.
3. Year Handling:
   • The year register (0x06) is only two digits (00 ~ 99).
   • Assume 20xx when displaying.
   • Example: 0x25 → 25 → display as 2025.
4. Day of Week:
   • Use a lookup table or switch-case to display a text label.
5. LCD Output:
   • Clear or overwrite the LCD before each update to prevent overlapping text.
6. Debugging Tip:
   • Before writing to the LCD, try sending the decoded values over UART to confirm your BCD conversions are correct.

Receive formatted commands from the host PC, parse them, and update the DS3231 date and time registers over I2C. Convert all values into BCD format before writing.

UART Command Formats for Updating RTC:

Rules

1. Date Handling:
   • Month, day, year → convert to BCD.
   • If the year is 4 digits, take yyyy % 100 to form a 2-digit BCD year.
   • Day-of-week → map string (SU…SA) into RTC value 1 ~ 7.
2. Time Handling:
   • Parse hours, minutes, seconds.
   • If a 12-hour format with AM/PM is provided:
     • Save to DS3231 in 12-hour mode (set bit 6 = 1).
     • Set bit 5 = 0 for AM, 1 for PM.
     • Save hours (01 ~ 12) in BCD.
   • If a 24-hour format is provided:
     • Save to DS3231 in 24-hour mode (set bit 6 = 0).
     • Hours encoded directly (00 ~ 23) in BCD.
   • Minutes and seconds → always in BCD.
3. I2C Write Sequence:
   Write registers in order:
   • 0x00 Seconds
   • 0x01 Minutes
   • 0x02 Hours (with format bits set as above)
   • 0x03 Day (1 ~ 7)
   • 0x04 Date (BCD)
   • 0x05 Month (BCD; century bit = 0 for 20xx)
   • 0x06 Year (two-digit BCD)
4. Verification:
   • After writing, Exercise 1’s LCD loop should show the updated time/date in 12-hour format with AM/PM.

Hits

• Always convert decimal → BCD before writing to RTC.
• For 12-hour mode, validate that 1 ≤ hh ≤ 12. For 24-hour mode, 0 ≤ hh ≤ 23.
• Echo parsed results over UART for debugging.