M34C00 データシートの表示（PDF） - STMicroelectronics
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M34C00 Datasheet PDF : 15 Pages
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M34C00
Read Operation
Following a Start condition, the bus master sends
a Device Select code with the RW bit set to 1. The
device acknowledges this, and outputs the byte in
location 00h. The counter is then incremented,
and the device continues to output the next byte in
sequence. To terminate the stream of bytes, the
bus master must not acknowledge the last byte
output, and must generate a Stop condition, as
shown in Figure 8.
The output data comes from consecutive
addresses, with the internal address counter
automatically incremented after each byte output.
After the last memory address, the internal
address counter rolls over, to continue reading
from the start of the memory.
Acknowledge in Read Mode
For all Read commands, the device waits, after
each byte read, for an acknowledgment during the
9th bit time. If the bus master does not pull Serial
Data (SDA) Low during this time, the device
terminates the data transfer and switches to its
Stand-by mode.
Setting the Write-Protection by Writing to the
Protection Register
The M34C00 has a software Write-protection
function, using the Protection Register, that allows
the bottom 16 bytes of the memory area
(addresses 00h to 0Fh) to be permanently Write-
Table 4. Write Time
WRITE to Array-0 (when not protected)
WRITE to Array-0 (when Write-protected)
WRITE to Array-1
WRITE to Array-2
Note: 1. For the value to tW please see Table 6.
Write
Time1
tW
0
tW
tW
protected. The Write-protection feature is
activated by writing once to the Protection
Register.
The Protection Register is written with the device
select code set to 0110.1110b (as shown in Figure
9). Address and data bytes must be sent with this
command, but their values are all ignored, and are
treated as Don’t Care. Once the Protection
Register has been written, the Write-protection of
the first 16 bytes of the memory is enabled, and it
is not possible to unprotect these 16 bytes, even if
the device is powered off and on.
When the Protection Register has been written,
the M34C00 no longer responds to the device type
identifier 0110b for either Read or Write
operations.
Figure 8. Read Sequence
SEQUENTIAL READ
of first N bytes
ACK
ACK
DEV SEL
DATA 0
R/W
ACK
NO ACK
DATA N-1
AI03717
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