07-08-2012, 02:31 PM
RTC (Real Time Clock)
[attachment=30382]
A RTC is a computer clock (most often in the form of an integrated circuit) that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.
The DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287. The devices provide a real-time clock/calendar, one time-of-day alarm, three mask able interrupts with a common interrupt output, a programmable square wave, and 114 bytes of battery-backed static RAM (113 bytes in the DS12C887 and DS12C887A).
We are using DS1307 64x8, Serial, Real Time Clock.
Features:
• Real-Time Clock (RTC) Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the week, and Year with Leap-Year Compensation Valid Up to 2100.
• 56-Byts of NV SRAM, Battery-Backed, General-Purpose RAM with Unlimited Writes.
• Address and data transferred serially through I2C bidirectional Serial bus Interface.
• Programmable Square-Wave Output Signal.
• Automatic Power-Fail Detect and Switch to the battery back-up Circuitry.
• Consumes Less than 500nA in Battery-Backup Mode with Oscillator Running.
• Optional Industrial Temperature Range: -40°C to +85°C.
• Available in 8-Pin Plastic DIP or SO.
• Underwriters Laboratories (UL) Recognized.
The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator.
The DS1307 operates as a slave device on the I2C bus. Access is obtained by implementing a START condition and providing a device identification code followed by a register address. Subsequent registers can be accessed sequentially until a STOP condition is executed.
VCC falls below 1.25 x VBAT, the device terminates an access in progress. VCC is greater than 1.25 x Vbat then it recognizes inputs.
PIN Diagram:
PIN Description:
X1 and X2
Connections for Standard 32.768 kHz Quartz Crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (CL) of 12.5Pf.
Vbat
Backup Supply Input for Any Standard 3V Lithium Cell or Other Energy Source. If a backup supply is not required, VBAT must be grounded. The nominal power-fail trip point (VPF) voltage at which access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal.
GND
Ground.
SDA
Serial Data Input/Output. SDA is the data input/output for the I2C serial interface. The SDA pin is open drain and requires an external pull-up resistor. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC.
SCL
Serial Clock Input. SCL is the clock input for the I2C interface and is used to synchronize
data movement on the serial interface. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC.
SQW/OUT
Square Wave/Output Driver. The SQWE bit set to 1, the SQW/OUT pin outputs one of four square-wave frequencies. SQW/OUT operates with either VCC or VBAT applied. If not used, this pin can be left floating.
VCC
Primary Power Supply. When a backup supply is connected to the device and VCC is below VTP, read and writes are inhibited.
[attachment=30382]
A RTC is a computer clock (most often in the form of an integrated circuit) that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.
The DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287. The devices provide a real-time clock/calendar, one time-of-day alarm, three mask able interrupts with a common interrupt output, a programmable square wave, and 114 bytes of battery-backed static RAM (113 bytes in the DS12C887 and DS12C887A).
We are using DS1307 64x8, Serial, Real Time Clock.
Features:
• Real-Time Clock (RTC) Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the week, and Year with Leap-Year Compensation Valid Up to 2100.
• 56-Byts of NV SRAM, Battery-Backed, General-Purpose RAM with Unlimited Writes.
• Address and data transferred serially through I2C bidirectional Serial bus Interface.
• Programmable Square-Wave Output Signal.
• Automatic Power-Fail Detect and Switch to the battery back-up Circuitry.
• Consumes Less than 500nA in Battery-Backup Mode with Oscillator Running.
• Optional Industrial Temperature Range: -40°C to +85°C.
• Available in 8-Pin Plastic DIP or SO.
• Underwriters Laboratories (UL) Recognized.
The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator.
The DS1307 operates as a slave device on the I2C bus. Access is obtained by implementing a START condition and providing a device identification code followed by a register address. Subsequent registers can be accessed sequentially until a STOP condition is executed.
VCC falls below 1.25 x VBAT, the device terminates an access in progress. VCC is greater than 1.25 x Vbat then it recognizes inputs.
PIN Diagram:
PIN Description:
X1 and X2
Connections for Standard 32.768 kHz Quartz Crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (CL) of 12.5Pf.
Vbat
Backup Supply Input for Any Standard 3V Lithium Cell or Other Energy Source. If a backup supply is not required, VBAT must be grounded. The nominal power-fail trip point (VPF) voltage at which access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal.
GND
Ground.
SDA
Serial Data Input/Output. SDA is the data input/output for the I2C serial interface. The SDA pin is open drain and requires an external pull-up resistor. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC.
SCL
Serial Clock Input. SCL is the clock input for the I2C interface and is used to synchronize
data movement on the serial interface. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC.
SQW/OUT
Square Wave/Output Driver. The SQWE bit set to 1, the SQW/OUT pin outputs one of four square-wave frequencies. SQW/OUT operates with either VCC or VBAT applied. If not used, this pin can be left floating.
VCC
Primary Power Supply. When a backup supply is connected to the device and VCC is below VTP, read and writes are inhibited.