MCP79400 datasheet(39/62 Pages) MICROCHIP

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DS20005009F-page 39

MCP79400/MCP79401/MCP79402

6.2.4

ACKNOWLEDGE POLLING

Since the device will not acknowledge an EEPROM

control byte during an internal EEPROM 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 6-7

for the flow diagram.

FIGURE 6-7:

ACKNOWLEDGE

POLLING FLOW

Send EEPROM

Write Command

Send Stop

Condition to

Initiate Write Cycle

Send Start

Send Control Byte

with R/W = 0

Did Device

Acknowledge

(ACK = 0)?

Operation

NO*

YES

Note*:

For added system robustness, implement

time-out checking to avoid a potential infinite loop.

Note:

For added systems robustness, it is

recommended that time-out functionality

be implemented in the acknowledge

polling routine to avoid potentially hanging

the system by entering an infinite loop.

This can easily be done by designing in a

maximum number of loops the routine will

execute, or through the use of a hardware

timer.

If a time out occurs, polling should be

aborted by sending a Stop condition. A

user-generated error-handling routine can

then be called, allowing the system to

recover in a manner appropriate for the

application.

MCP79400 Datasheet(PDF) 39 Page - Microchip Technology

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