BU9877FV Datasheet, PDF (6/9 Pages) Rohm – Serial interface IC for DIMMs supporting plug & play

Memory ICs
BU9877FV
(7) Write protect command
The write protect command is used to prohibit writing of
data to addresses 00 to 7Fh, among the 256 word
address data. Be aware that once a write protect regis-
ter has been specified, it cannot be canceled (one-time
memory). The write protect command can function
regardless of the state of the WP pin.
(8) WP (write protect pin)
Setting the WP pin to Vcc (HIGH level) has the same
effect as using the write protect command, and inhibits
writing of data to addresses 80 to FFh, among the 256
word address data. Normal writing is enabled by set-
ting this pin to GND (LOW level). (If the write protect
command is used to inhibit writing, data cannot be writ-
ten regardless of the status of the WP pin.) The WP pin
is equipped with an internal pull-down resistor, so if the
protect function is not being used, this should be left
open or set to GND.
(9) ACK signal
The acknowledge signal (ACK signal) is determined by
the software, and indicates whether or not the data has
been correctly transmitted. Regardless of whether the
address is a master or slave address, the device on the
transmitter (sending signal) side (the master when a
slave address is input for a write command or a read
command, and the EEPROM when read command
data is output) opens the bus after this 8-bit data is out-
put. With a device on the receiving (reception) side (the
EEPROM when a slave address is input for a read
command or write command, and the master when
data is output for a read command), SDA is set to LOW
during the nine-clock cycle, and the acknowledge sig-
nal (ACK signal) is output when 8-bit data is received.
For writing operations, the acknowledge signal (ACK
signal) is output in the LOW state each time that 8-bit
data (word address or write data) is received.
In reading operations, 8-bit data (read data) is output,
and then the acknowledge signal (ACK signal) in the
LOW state is detected. If the acknowledge signal (ACK
signal) is detected and no stop condition is sent from
the master (microcomputer) side, this IC continues to
output data. If the acknowledge signal (ACK signal) is
not detected, this IC interrupts the transmission of data,
recognizes a stop condition (stop bit), and terminates
the reading operation. The IC then enters the standby
mode.
Start condition
SCL
(from master)
1
t PD
8
9
SDA
(master output data)
SDA
(data output from the BU9877FV)
6
Acknowledge signal (ACK signal)
Fig. 6 Acknowledge signal (ACK signal) response
(when slave address is input for writing or reading)