X1227S8IZ-4.5A
| Model | X1227S8IZ-4.5A |
| Description | 2-Wire RTC Real TimeClock/Calendar/CPU Supervisor with EEPROM |
| PDF file | Total 28 pages (File size: 419K) |
| Chip Manufacturer | INTERSIL |
X1227
Acknowledge Polling
Disabling of the inputs during nonvolatile write cycles
can be used to take advantage of the typical 5mS write
cycle time. Once the stop condition is issued to indi-
cate the end of the master’s byte load operation, the
X1227 initiates the internal nonvolatile write cycle.
Acknowledge polling can begin immediately. To do
this, the master issues a start condition followed by the
Memory Array Slave Address Byte for a write or read
operation (AEh or AFh). If the X1227 is still busy with
the nonvolatile write cycle then no ACK will be
returned. When the X1227 has completed the write
operation, an ACK is returned and the host can pro-
ceed with the read or write operation. Refer to the flow
chart in Figure 16. Note: Do not use the CCR slave
byte (DEh or DFh) for acknowledge polling.
Read Operations
There are three basic read operations: Current
Address Read, Random Read, and Sequential Read.
Current Address Read
Internally the X1227 contains an address counter that
maintains the address of the last word read incre-
mented by one. Therefore, if the last read was to
address n, the next read operation would access data
from address n+1. On power-up, the sixteen bit
address is initialized to 0h. In this way, a current
address read immediately after the power-on reset
can download the entire contents of memory starting
at the first location.Upon receipt of the Slave Address
Byte with the R/W bit set to one, the X1227 issues an
acknowledge, then transmits eight data bits. The mas-
ter terminates the read operation by not responding
with an acknowledge during the ninth clock and issu-
ing a stop condition. Refer to Figure 15 for the
address, acknowledge, and data transfer sequence.
Figure 15. Current Address Read Sequence
Signals from
the Master
SDA Bus
Signals from
the Slave
S
t
a
r
t
1
Slave
Address
S
t
o
p
YES
Continue normal
Read or Write
command
sequence
Figure 16. Acknowledge Polling Sequence
Byte load completed
by issuing STOP.
Enter ACK Polling
Issue START
Issue Memory Array Slave
Address Byte AFh (Read)
or AEh (Write)
NO
Issue STOP
ACK
returned?
YES
nonvolatile write
Cycle complete. Continue
command sequence?
NO
Issue STOP
PROCEED
It should be noted that the ninth clock cycle of the read
operation is not a “don’t care.” To terminate a read
operation, the master must either issue a stop condi-
tion during the ninth cycle or hold SDA HIGH during
the ninth clock cycle and then issue a stop condition.
1 1 11
A
C
K
Data
21
FN8099.1
September 15, 2005
