MCP79402 datasheet(11/62 Pages) MICROCHIP

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DS20005009F-page 11

MCP79400/MCP79401/MCP79402

5.0

FUNCTIONAL DESCRIPTION

The MCP7940X is a highly-integrated Real-Time

Clock/Calendar (RTCC). Using an on-board, low-power

oscillator, the current time is maintained in seconds,

minutes, hours, day of week, date, month, and year. The

MCP7940X also features 64 bytes of general purpose

SRAM and eight bytes of protected EEPROM. Two

alarm modules allow interrupts to be generated at

specific times with flexible comparison options. Digital

trimming can be used to compensate for inaccuracies

inherent with crystals. Using the backup supply input

and an integrated power switch, the MCP7940X will

automatically switch to backup power when primary

power is unavailable, allowing the current time and the

SRAM contents to be maintained. The time-stamp

module captures the time when primary power is lost

and when it is restored.

The RTCC configuration and status registers are used to

access all of the modules featured on the MCP7940X.

5.1

Memory Organization

The MCP7940X features three different blocks of

memory: the RTCC registers, general purpose SRAM,

and protected EEPROM. The RTCC registers and

SRAM share the same address space, accessed

through the ‘1101111X’ control byte. The protected

EEPROM is in a separate address space and is

accessed

using

the

‘1010111X’

control

byte

(Figure 5-1). Unused locations are not accessible. The

MCP7940X will not acknowledge if the address is out of

range, as shown in the shaded region of the memory

map in Figure 5-1.

The RTCC registers are contained in addresses

0x00-0x1F. Table 5-1 shows the detailed RTCC register

map. There are 64 bytes of user-accessible SRAM,

located in the address range 0x20-0x5F. The SRAM is a

separate block from the RTCC registers. All RTCC

registers and SRAM locations are maintained while

operating from backup power.

The protected EEPROM section is located in addresses

0xF0-0xF7.

FIGURE 5-1:

MEMORY MAP

Time and Date

SRAM (64 Bytes)

Power-Fail Time-Stamp

Alarm 1

Alarm 0

Configuration and Trimming

0x00

0x06

0x07

0x09

0x0A

0x10

0x11

0x17

0x18

0x1F

0x20

0x5F

0x60

0xFF

Unimplemented; device does not ACK

I2C Address: 1101111x

RTCC Registers/SRAM

Protected EEPROM (8 Bytes)

0x00

0xEF

0xF0

0xF7

0xF8

0xFF

Unimplemented; device does not ACK

I2C Address: 1010111x

EEPROM

EUI-48/EUI-64 Node Address

Unimplemented; device does not ACK

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