x4c105 Intersil Corporation, x4c105 Datasheet - Page 8

• Manufacturer Part Number: x4c105
• Description: Cpu Supervisor With Novram And Output Ports
• Manufacturer: Intersil Corporation

Figure 9. Current Address Read Sequence
Figure 10. Random Address Read Sequence
The device offers a similar operation, called “Set Cur-
rent Address,” where the device ends the transmission
and issues a stop instead of the second start, shown in
Figure 10. The device goes into standby mode after
the stop and all bus activity will be ignored until a start
is detected. This operation loads the new address into
the address counter. The next current address read
operation will then read from the newly loaded
address. This operation could be useful if the master
knows the next address it needs to read, but is not
ready for the data.
Sequential Read
Sequential reads can be initiated as either a current
address read or random address read. The first data
byte is transmitted as with the other modes; however,
the master now responds with an acknowledge, indicat-
ing it requires additional data. The device continues to
output data for each acknowledge received. The master
terminates the read operation by not responding with an
acknowledge and then issuing a stop condition.
Signals from
Signals from
the Master
the Slave
SDA Bus
8
Signals from
Signals from
S
a
t
r
t
the Master
the Slave
SDA Bus
Address
Slave
0
S
a
t
r
t
A
C
K
Address
Address
Slave
Byte
X4C105
1
The data output is sequential, with the data from address
n followed by the data from address n + 1. The address
counter for read operations increments through all page
and column addresses, allowing the entire memory con-
tents to be serially read during one operation. At the end
of the address space the counter “rolls over” to address
0000
acknowledge received. Refer to Figure 11 for the
acknowledge and data transfer sequence.
SERIAL DEVICE ADDRESSING
Slave Address Byte
Following a start condition, the master must output a
slave address byte. This byte consists of several parts:
– a device type identifier that is always ‘1010’.
– two bits that provide the device select bits.
– one bit that becomes the MSB of the address.
– one bit of the slave command byte is a R/W bit. The
A
C
K
A
C
K
R/W bit of the slave address byte defines the opera-
tion to be performed. When the R/W bit is a one,
then a read operation is selected. A zero selects a
write operation. Refer to Figure 12.
S
a
t
r
t
H
and the device continues to output data for each
Address
Data
Slave
1
A
C
K
S
o
p
t
Data
S
o
p
t
March 18, 2005
FN8124.0