© 1998 Microchip Technology Inc.

DS11183E-page 7

24C04A

7.0

ACKNOWLEDGE POLLING

Since the device will not acknowledge during a 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 com-

mand has been issued from the master, the device ini-

tiates the internally timed write cycle. ACK polling can

be initiated immediately. This involves the master send-

ing 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 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 7-1 for flow diagram.

FIGURE 7-1:

ACKNOWLEDGE POLLING

FLOW

Send

Write Command

Send Stop

Condition to

Initiate Write Cycle

Send Start

Send Control Byte

with R/W = 0

Did Device

Acknowledge

(ACK = 0)?

Next

Operation

NO

YES

8.0

WRITE PROTECTION

Programming of the upper half of the memory will not

The device will accept slave and word addresses but if

the memory accessed is write protected by the WP pin,

the 24C04A will not generate an acknowledge after the

first byte of data has been received, and thus the pro-

gram cycle will not be started when the STOP condition

is asserted.