Digilent 410-218P User Manual

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Revision: October 17, 2011
Note: This document applies to REV A of the board.

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Overview

The PmodRTCC is a real-time clock/calendar
powered by the Microchip MCP79410.

Features include:

• a real-time clock/calendar with lithium
coin cell back-up

• an I2C interface

• multi-function pin output that can

generate a square wave

• two available alarms

• 128 bytes EEPROM

• 64 bytes SRAM

Functional Description

The PmodRTCC can communicate using I2C
via the 8-pin header J2. Digilent boards
implement several different I2C interfaces. For
more information, see the Connecting I2C
Interfaces document available at

www.digilentinc.com.

Interface

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.

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.

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Connector J2 – I2C Communications
Pin Signal Description

1, 2 SCL I2C Clock
3, 4 SDA I2C Data
5, 6 GND Power Supply Ground
7, 8 VCC Power Supply (3.3V)

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.

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.

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PmodRTCC Reference Manual

Connector J1 – MFP Header
Pin Signal Description

1 MFP Multi-Function Pin
2 GND Power Supply Ground

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 2-10K-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.

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.

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.

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Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.