BV4208. I2C-RTC & Temp. Sensor. Product specification. November 2008 V0.a. ByVac Page 1 of 5

Transcription

1 BV4208 Product specification November 2008 V0.a ByVac Page 1 of 5

2 Contents 1. Introduction Features RTC Features Temp. Sens Electrical Specification Circuit Diagram Data Sheets Examples The temperature sensor The Real Time Clock...4 ByVac Page 2 of 5

3 Rev Nov Nov Change Preliminary 1. Introduction PCB is now the same as the BV4237 The is a small circuit board that contains a M41T81 Real Time Clock with alarms and also an MCP9802 High Accuracy Temperature Sensor. From November 2010, the uses the same PCB as the BV4237 but does not have the microcontroller populated. 5. Circuit Diagram The circuit diagram is shown at the back of this text 6. Data Sheets This data sheet should be read in conjunction with the M41T81 and MPC9802 data sheets from the chip manufactures. Both sheets are also on the ByVac web site ( 7. Examples The following examples are using the BV4221, USB to I2C convertor to drive the in this arrangement: 2. Features RTC I2C up to 400kHz Detects power down and saves time Battery back up Programmable Alarm Watchdog timer RTO Output 3. Features Temp. Sens. 12 bit resolution Operating Current 1uA Power saving mode -55 C to +125 C Alert output 4. Electrical Specification NOTE: This picture shows the older version of the BV The temperature sensor The temperature sensor address is 0x90 and has 4 writeable addresses 0-3 that control how it works. For this example the default setting of 9 bit resolution is taken. To read the temperature write 0 first thus: 0x90>s 0 r g-2 p The above, first writes 0 which selects the temperature register and then it reads from address 0x91 two bytes. The temperature will be displayed in hex. This version of the PCB does not have the microcontroller populated, just the RTC and Temperature sensor. RTO can be found at pin 1 as shown. The RTC clock has its own 32kHz crystal and there is a battery holder to take a standard CR1220 lithium battery. ByVac Page 3 of 5

4 register. The following write to the consecutive registers. To read back the time including the Tenths/Hundredths of a second, address 0 again as follows. 0xD0>s 0 r g-4 p Read the first four bytes for the timekeeper register. To just read the minutes and seconds, address the second byte of the register before reading. The first reading shows a temperature of 0x16 (22 C) and the second reading, after warming the IC with the fingers reads 27.5 C. The 0x1b is 27 and the 0x80 is 0.5, this is the default 9bit resolution, the 9 th bit is either 0.0 or 0.5 degrees The Real Time Clock The RTC needs a battery to operate and this should be fitted to the battery holder provided. The + sign points away from the PCB. The RTC address is 0xD0 The RTC is very easy to read and write as it has a set of registers that can be addressed in a similar way to a memory location. The registers are allocated as follows: 1. Tenths/Hundredths of a Second Register 2. Seconds Register 3. Minutes Register 4. Century/Hours Register 5. Day Register 6. Date Register 7. Month Register 8. Year Register 9. Control Register 10. Watchdog Register Alarm Registers Reserved 20. Square Wave Register To set the time to 15:10 for example: 0xD0>s p 0xD0>s 2 r g-2 p An example of this is given in the screen shot below. When power is removed form the RTC it will retain the current time and this can be read using the above. The clock will appear to have stopped until the HT flag is cleared, this must be done for each power down/up cycle. 0xD0>s c 0 p Clearing the HT flag The above are just some simple pointers to getting the RTC going. The IC is a very comprehensive timekeeper. To get the best form it this must be read in conjunction with the appropriate datasheet. The first 0, addresses the timekeeper register to point to the Tenths/Hundredths of a second ByVac Page 4 of 5

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