24lc21a Microchip Technology Inc., 24lc21a Datasheet - Page 11

• Manufacturer Part Number: 24lc21a
• Description: 1k 2.5v Dual Mode I2c Serial Eeprom
• Manufacturer: Microchip Technology Inc.

5.0
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
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 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:
 2003 Microchip Technology Inc.
ACKNOWLEDGE POLLING
Initiate Write Cycle
Send Control Byte
Write Command
Acknowledge
with R/W = 0
Condition to
(ACK = 0)?
Did Device
Send Start
Send Stop
Operation
Send
Next
ACKNOWLEDGE
POLLING FLOW
Yes
No
6.0
When using the 24LC21A in the Bidirectional mode, the
VCLK pin can be used as a write-protect control pin.
Setting VCLK high allows normal write operations,
while setting VCLK low prevents writing to any location
in the array. Connecting the VCLK pin to V
allow the 24LC21A to operate as a serial ROM,
although this configuration would prevent using the
device in the Transmit-only mode.
WRITE PROTECTION
24LC21A
DS21160F-page 11
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