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1300 Henley Court Pullman, WA 99163 509.334.6306 www.digilentinc.com PmodRTCC™ Reference Manual Revised May 24, 2016 This manual applies to the PmodRTCC rev. A Overview The PmodRTCC is a real-time clock/calendar powered by the Microchip® MCP79410. Through the I2C interface, users may configure up to two alarms that can be triggered at a wide variety of possible times. Features include:          The PmodRTCC. 1 Real-time clock/calendar with lithium coin cell back-up Multi-function pin output that can generate a square wave Two available alarms 128 bytes EEPROM 64 bytes SRAM Small PCB size for flexible designs 1.3“ × 0.8” (3.3 cm × 2.0 cm) 2×4-pin connector with I2C interface Follows Digilent Pmod Interface Specification Library and example code available in resource center Functional Description The PmodRTCC can communicate using I2C via the 8-pin header J2. Digilent boards implement several different I2C interfaces. 2 Interfacing with the Pmod All communications with the device must specify whether to write to the EEPROM or the RTCC registers/SRAM, as well as a register address and a flag indicating whether the communication is a read or a write. This is followed by the actual data transfer. The PmodRTCC responds to two I2C addresses. Address ‘1010111’ is used for access to the EEPROM, and address ‘1101111’ is used for access to RTCC registers/SRAM. DOC#: 502-218 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 1 of 2 PmodRTCC™ Reference Manual The device is configured by writing to the registers within the device. The time registers can be set to specific values and a control register sets their functionality. Pin 1&5 2&6 3&7 4&8 Signal SCL SDA GND VCC Description Serial Clock Serial Data Power Supply Ground Power Supply (3.3V/5V) Table 1. Pinout description table. A full list of registers and their functionality, as well as communication specifications, can be found in the MCP79410 datasheet available at the Microchip website. The I2C interface standard uses two signal lines. These are I2C data (SDA) and serial clock (SCLK). These signals map to the serial data (SDA) and serial clock (SCLK) on the MCP79410. 2.1 Power Back-up The PmodRTCC has a holder for a 12mm lithium coin cell to power the RTCC and SRAM if VDD should ever fall below the operating point. In order to enable this power back-up, the VBATEN bit must be set in the RTCC registers. Compatible coin cells include BR1216, CR1216, BR1220, CL1220, CR1220, and BR1225. Pin 1 Connector J1 – MFP Header Signal Description MFP Multi-Function Pin 2 GND Power Supply Ground Table 2. MFP header. 2.2 Multi-Function Pin (MFP) The MFP can be accessed via the 2-pin header J1. The MFP has an open drain output. To use it, an external 3.3V 210K-ohm pull-up resistor is required. The MFP can have several different functions including user-controllable output, alarm output, and clock frequency output, depending on the settings in the RTCC registers. Settings and functions are described in the MFP section of the MCP79410 datasheet. 2.3 Alarms The MCP79410 has two alarms. Each can be set to trigger an alarm interrupt flag at a particular time, driving the MFP high or low depending on how the polarity bit is set. 2.4 Calibration The Calibration register in the MCP79410 can calibrate the device to correct for inaccuracies of the input clock source. It can add or subtract up to 254 clocks from the RTCC counter every minute. For more information, see the Calibration section of the MCP74910 datasheet. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 2 of 2