Chapter 9: Using User Flash Memory in MAX II Devices
9–33
Software Support for UFM Block
internal program cycle in the UFM, RDSRis the only valid opcode recognized by the
interface (therefore, the status register can be read at any time), and nRDYis the only
valid status bit. Other status bits are frozen and remain unchanged until the internal
program cycle is ended. RDSRis issued through the following sequence, as shown in
Figure 9–35:
1. nCSis pulled low.
2. Opcode 00000101is transmitted into the interface.
3. SIignores incoming signals; SOoutput the content of the status register, Bit7
first and Bit0last.
4. If nCSis kept low, repeat step 3.
5. nCSis pulled back to high to terminate the transmission.
Figure 9–35. RDSR Operation Sequence
nCS
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
SCK
SI
8-bit
Instruction
05H
MSB
MSB
High Impendance
SO
Status Register Out
MSB
MSB
WRSR (Write Status Register)
The block protection bits(BP1and BP0) are the status bits used to protect certain
sections of the UFM from inadvertent write. The BP1and BP0status are updated by
WRSR. During WRSR, only BP1and BP0in the status register can be written with valid
information. The rest of the bits in the status register are ignored and not updated.
When both BP1and BP0are 0, there is no protection for the UFM. When both BP1
and BP0are 1, there is full protection for the UFM. BP0and BP1are set to 0 upon
power-up. Table 9–12 describe more on the Block Write Protect Bits for Extended
mode, while Table 9–13 describes more on the Block Write Protect Bits for Base mode.
WRSRis issued through the following sequence, as shown in Figure 9–36:
1. nCSis pulled low.
2. Opcode 00000001is transmitted into the interface.
3. An 8-bit status is transmitted into the interface to update BP1and BP0of the status
register.
4. If nCSis pulled high too early (before all the eight bits in Step 2 or Step 3 are
transmitted) or too late (the ninth bit or more is transmitted), WRSRis not executed.
© October 2008 Altera Corporation
MAX II Device Handbook
ALTERA [ ALTERA CORPORATION ]
