MCP79401 datasheet(9/38 Pages) MICROCHIP

Part #	MCP79401

Description	I2C??Real-Time Clock/Calendar with SRAM, Unique ID and Battery Switchover

PDF	38 Pages

Scroll/Zoom	100%

Manufacturer	MICROCHIP [Microchip Technology]

Direct Link	http://www.microchip.com

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9 / 38 page

 2011 Microchip Technology Inc.

DS25009A-page 9

MCP7940X

3.1.3

ACKNOWLEDGE POLLING

Since the device will not acknowledge a Unique ID

command during an ID write cycle, this can be used to

determine when the cycle is complete. This feature can

be used to maximize bus throughput. Once the Stop

condition for a Write command has been issued from

the master, the device initiates the internally timed write

cycle. ACK polling can be initiated immediately. This

involves the master sending a Start condition, followed

by the control byte for a Write command (R/W = 0). If

the device is still busy with the write cycle, then no ACK

will be returned. If no ACK is returned, then the Start bit

and control byte must be resent. If the cycle is

complete, then the device will return the ACK, and the

master can then proceed with the next Read or Write

command. See Figure 3-4 for the flow diagram.

FIGURE 3-4:

ACKNOWLEDGE

POLLING FLOW

Send

ID Write Command

Send Stop

Condition to

Initiate ID Write Cycle

Send Start

Send Control Byte

with R/W = 0

Did Device

Acknowledge

(ACK = 0)?

Operation

YES

MCP79401 Datasheet(PDF) 9 Page - Microchip Technology