© 1996 Microchip Technology Inc.

DS21140B-page 9

24LC41

5.0

ACKNOWLEDGE POLLING

Acknowledge polling can be done for both the DDC

Monitor Port (when in bi-directional Mode) and the

Microcontroller Access Port.

Since the port 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 but

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 5-1 for the flow diagram.

FIGURE 5-1:

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

6.0

WRITE PROTECTION

6.1

DDC Monitor Port

When using the DDC Monitor Port in the bi-directional

Mode, the VCLK/DWP pin operates as the write protect

control pin. Setting VCLK/DWP high allows normal

write operations, while setting VCLK/DWP low prevents

writing to any location in the array. Connecting the

Port to operate as a serial ROM, although this configu-

ration would prevent using the device in the Transmit-

Only Mode.

6.2

Microcontroller Access Port

The Microcontroller Access Port can be used as a

Programming will be inhibited and the entire memory

associated with the Microcontroller Access Port will be

write-protected.

7.0

READ OPERATION

Read operations are initiated in the same way as write

operations with the exception that the R/W bit of the

slave address is set to one. There are three basic types

of read operations: current address read, random read

and sequential read. These operations are identical for

both the DDC Monitor Port (in bi-directional Mode) and

the Microcontroller Access Port and are completely

independent of one another.

7.1

Current Address Read

The port contains an address counter that maintains

the address of the last word accessed, internally incre-

mented by one. Therefore, if the previous access (either

a read or write operation) was to address n, the next

current address read operation would access data from

address n + 1. Upon receipt of the slave address with

R/W bit set to one, the port issues an acknowledge and

transmits the 8-bit data word. The master will not

acknowledge the transfer but does generate a stop con-

dition and the port discontinues transmission (Figure 7-

1).

7.2

Random Read

Random read operations allow the master to access

any memory location in a random manner. To perform

this type of read operation, first the word address must

be set. This is done by sending the word address to the

port as part of a write operation. After the word address

is sent, the master generates a start condition following

the acknowledge. This terminates the write operation,

but not before the internal address pointer is set. The

master then issues the control byte again, but with

the R/W bit set to a one. The port then issues an

acknowledge and transmits the 8-bit data word. The

master will not acknowledge the transfer but does gen-

erate a stop condition and the port discontinues trans-

mission (Figure 7-2).