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DS1302 Driver development part 1
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‎blog/content/ds1302_p1.md

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title = "DS1302 RTC Drivers for STM32 Part 1"
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date = 2024-08-24
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[taxonomies]
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tags = ["platformio", "stm32", "stm32-pio-libs"]
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# Introduction
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The DS1302 is a Real-Time Clock (RTC) IC used to keep track of time and date. It has the capability to store data such as seconds, minutes, hours, day, date, month, and year. The DS1302 can be interfaced with microcontrollers using a simple serial communication protocol (SPI-like but with slight differences). It also includes 31 bytes of static RAM for temporary data storage.
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{{ image(src="/img/ds1302_module.png", position="center", style="width:50%;") }}
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<br>
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<br>
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# Interface with module
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### Pinout
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{{ image(src="/img/ds1302_pinout.png", position="center", style="width:70%;") }}
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Above is the pinout of DS1302. This is description of each pin.
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+ **V<sub>cc2</sub>**: This is the main power supply which you connect to any 3.3v or 5v power source.
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+ **V<sub>cc1</sub>**: Connect a flat lithium sound button cell which powers the low power operation i.e. keeping the clock ticking.
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+ **X1/X2**: Connect any 32.768kHz Quartz Crystal.
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+ **GND**: Just a ground
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+ **CE**: When Chip Enable pin is set high, it initiates the data transfer. It is kept high till the data transfer is being done.
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+ **I/O**: This pin is used to send and receive data.
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+ **SCLK**: The microcontroller generates clock on this line, this clock is used to synchronise the MCU and DS1302.
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## Communication
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Communication happens in following step.
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1. Set the `CE` pin high to initiate data transfer
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2. Start to produce clock signal on `SCLK` pin.
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3. First MCU writes the first byte which is the address it want to communicate.
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+ If MCU wants to write, send the next byte which is the data.
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+ If MCU wants to read, set its pin in input mode and read the coming data from DS1302.
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{{ image(src="/img/ds1302_communication.png", position="center", style="width:100%;") }}
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## Addressing
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{{ image(src="/img/ds1302_addressmap.png", position="center", style="width:100%;") }}
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The address space in ds1302 is divided into two parts.
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+ **Clock/Calendar**: If the `bit 6` is set to low, it allows you to access Clock/Calendar space. This is where datetime information is stored.
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+ **RAM**: If the `bit 6` is set to high, it allows you to access the RAM space. DS1302 provides your 31 bytes of storage where you can write or ready any personal data. It is a non-volatile storage space useful to store some configuration data.
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The `bit 7` is always set to high, The `bit 0` lets your specify read or write operation, write operation when set to low and read operation when set to high. `Bit 1-5` used to specify address from 0-31.
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### Clock/Calendar address
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There are only 7 bytes useful to read or write in Clock/Calendar address space.
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0. Byte -> Second
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1. Byte -> Minutes
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2. Byte -> Hour
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3. Byte -> Date
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4. Byte -> Month
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5. Byte -> Day
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6. Byte -> Year
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Lets try to calculate some address ourself:
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+ How to read Month data
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```
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Month address -> 4 -> 0b00100
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B7 C/R A4 A3 A2 A1 A0 R/W
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Address Byte: 1 0 0 0 1 0 0 1
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```
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+ How to write year data
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```
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Year address -> 6 -> 0b00110
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B7 C/R A4 A3 A2 A1 A0 R/W
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Address Byte: 1 0 0 0 1 1 0 0
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```
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### Ram address
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You can access to all 31 bytes to read and write data from the RAM address space
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Lets try to calculate some address ourself:
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+ How to read from address 0
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```
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Month address -> 0 -> 0b00000
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B7 C/R A4 A3 A2 A1 A0 R/W
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Address Byte: 1 1 0 0 0 0 0 1
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```
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+ How to write to address 31
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```
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Year address -> 30 -> 0b11110
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B7 C/R A4 A3 A2 A1 A0 R/W
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Address Byte: 1 1 1 1 1 1 0 0
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```
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### Clock/Calendar data
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Data representation of DS1302 is rather different, I though it just stored the numbers directly in binary but it rather uses a different approach called BCD(binary-coded decimal) which first splits a decimal number into its individual digits and convert each decimal digit to binary using 4 bits.
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Here is an example for BCD
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```
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Decimal Number: 56
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Binary Value: 00111000
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Decimal Digit: 5 6
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BCD Value: 0101 0110
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```
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This is the complete Clock/Calendar datamap I took from the DS1302 datasheet. Lets go though them one by one
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{{ image(src="/img/ds1302_datamap.png", position="center", style="width:100%;") }}
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#### Seconds
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td>CH</td> <td colspan=3> 10 Second</td> <td colspan=4>Seconds</td> <td>00-59</td>
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</tr>
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</table>
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+ `Bit 7` of second is `CH(Clock Halt)`, when this bit is set high the clock is set to halt and stops ticking and continue ticking when you set low.
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+ `Bit 6-4` is the BCD representation of the tens digit of the second value eg. 5 in 56, 3 in 32. Range:0-5
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+ `Bit 3-0` is the BCD representation of the ones digit of the second value eg. 6 in 56, 2 in 32. Range:0-9
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> **Example:** Data value for 56 second would be 0b01010110
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#### Minutes
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td></td> <td colspan=3> 10 Minutes</td> <td colspan=4>Minutes</td> <td>00-59</td>
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</tr>
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</table>
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+ `Bit 7` is left empty i.e. logic 0
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+ `Bit 6-4` is the BCD representation of the tens digit of the minutes value eg. 5 in 56, 3 in 32. Range:0-5
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+ `Bit 3-0` is the BCD representation of the ones digit of the minutes value eg. 6 in 56, 2 in 32. Range:0-9
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#### Hour
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Hour is bit tricky because it operates in two modes i.e. 12 and 24 hrs.
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td rowspan=2>12/<span style="text-decoration: overline;">24</span></td>
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<td rowspan=2>0</td> <td>10</td> <td rowspan=2>Hour</td>
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<td rowspan=2 colspan=4>Hour</td> <td>0-23</td>
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</tr>
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<tr>
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<td><span style="text-decoration: overline;">AM</span>/PM</td><td>1-12</td>
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</tr>
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</table>
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+ If `Bit 7` is high then 12 hour mode selected
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+ `Bit 5` represent the meridiem. PM if High and AM if Low.
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+ `Bit 4` is the BCD representation of the tens digit of the minutes value. Range:0-1
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+ `Bit 3-0` is the BCD representation of the ones digit of the minutes value. Range:0-9
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+ If `Bit 7` is low then 24 hour mode selected
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+ `Bit 5-4` is the BCD representation of the tens digit of the minutes value. Range:0-2
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+ `Bit 3-0` is the BCD representation of the ones digit of the minutes value. Range:0-9
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+ `Bit 6` unused bit, so should set to low
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Example:
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```
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Time: 7:45 PM
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Hour: 7, Mode: 12hrs, Meridiem: PM
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Mode B6 Mer H10 -----H1------
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Data: 1 0 1 0 0 1 1 1
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Time: 17:46
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Hour: 17, Mode: 24hrs
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Mode B6 ---H10-- -----H1------
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Data: 0 0 1 1 0 1 1 0
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```
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#### Date
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td>0</td> <td>0</td><td colspan=2> 10 Date</td> <td colspan=4>Date</td> <td>1-31</td>
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</tr>
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</table>
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+ `Bit 7-6` unused leave empty i.e. logic 0
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+ `Bit 5-4` is the BCD representation of the tens digit of the Date value. Range:0-3
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+ `Bit 3-0` is the BCD representation of the ones digit of the Date value. Range:0-9
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#### Month
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td>0</td> <td>0</td><td>0</td><td colspan=1> 10 month</td> <td colspan=4>month</td> <td>1-12</td>
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</tr>
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</table>
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+ `Bit 7-5` unused leave empty i.e. logic 0
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+ `Bit 4` is the BCD representation of the tens digit of the month value. Range:0-1
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+ `Bit 3-0` is the BCD representation of the ones digit of the month value. Range:0-9
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#### Day
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td>0</td><td>0</td><td>0</td><td>0</td><td>0</td> <td colspan=3> Day</td>
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</tr>
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</table>
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+ `Bit 7-3` unused leave empty i.e. logic 0
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+ `Bit 2-0` represent day of the week, range: 1-7
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#### Year
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<table>
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<tr>
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<th>BIT 7</th> <th>BIT 6</th> <th>BIT 5</th> <th>BIT 4</th> <th>BIT 3</th> <th>BIT 2</th> <th>BIT 1</th> <th>BIT 0</th> <th>RANGE</th>
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</tr>
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<tr>
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<td colspan=4> 10 year</td> <td colspan=4>year</td> <td>00-99</td>
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</tr>
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</table>
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+ `Bit 7-4` is the BCD representation of the tens digit of the year value. Range:0-9
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+ `Bit 3-0` is the BCD representation of the ones digit of the year value. Range:0-9

‎blog/static/img/ds1302_addressmap.png

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‎blog/static/img/ds1302_communication.png

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‎blog/static/img/ds1302_datamap.png

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‎blog/static/img/ds1302_module.png

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‎blog/static/img/ds1302_pinout.png

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‎blog/templates/shortcodes/image.html

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{% if src %}
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{# If the image's URL is internal to the site... #}
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{% if src is not starting_with("http") %}

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