Instructions
M95640-W M95640-R M95640-DF
When the Status Register Write Disable (SRWD) bit in the Status Register is set to 1, two
cases should be considered, depending on the state of the Write Protect (W) input pin:
●
If Write Protect (W) is driven high, it is possible to write to the Status Register (provided
that the WEL bit has previously been set by a WREN instruction).
●
If Write Protect (W) is driven low, it is not possible to write to the Status Register even if
the WEL bit has previously been set by a WREN instruction. (Attempts to write to the
Status Register are rejected, and are not accepted for execution). As a consequence,
all the data bytes in the memory area, which are Software-protected (SPM) by the
Block Protect (BP1, BP0) bits in the Status Register, are also hardware-protected
against data modification.
Regardless of the order of the two events, the Hardware-protected mode (HPM) can be
entered by:
●
either setting the SRWD bit after driving the Write Protect (W) input pin low,
or driving the Write Protect (W) input pin low after setting the SRWD bit.
●
Once the Hardware-protected mode (HPM) has been entered, the only way of exiting it is to
pull high the Write Protect (W) input pin.
If the Write Protect (W) input pin is permanently tied high, the Hardware-protected mode
(HPM) can never be activated, and only the Software-protected mode (SPM), using the
Block Protect (BP1, BP0) bits in the Status Register, can be used.
6.5
Read from Memory Array (READ)
As shown in Figure 11, to send this instruction to the device, Chip Select (S) is first driven
low. The bits of the instruction byte and address bytes are then shifted in, on Serial Data
Input (D). The address is loaded into an internal address register, and the byte of data at
that address is shifted out, on Serial Data Output (Q).
Figure 11. Read from Memory Array (READ) sequence
S
0
1
2
3
4
5
6
7
8
9
10
20 21 22 23 24 25 26 27 28 29 30 31
C
Instruction
16-Bit Address
15 14 13
MSB
3
2
1
0
D
Q
Data Out 1
Data Out 2
High Impedance
2
7
6
5
4
3
1
7
0
MSB
AI01793D
1. Depending on the memory size, as shown in Table 5, the most significant address bits are Don’t Care.
If Chip Select (S) continues to be driven low, the internal address register is incremented
automatically, and the byte of data at the new address is shifted out.
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Doc ID 16877 Rev 16
STMICROELECTRONICS [ ST ]
