7–32
Chapter 7: User Flash Memory in MAX V Devices
Software Support for UFM Block
WRDI (Write Disable)
After the UFM is programmed, WRDIcan be issued to set WENback to
0, disabling WRITE
and preventing inadvertent writing to the UFM. WRDIis issued through the following
sequence, as shown in Figure 7–29:
1. nCSis pulled low.
2. Opcode 00000100is transmitted to set WENto
0in the status register.
3. After the transmission of the eighth bit of WRDI, the interface is in wait state
(waiting for nCSto be pulled back to high). Any transmission after this is ignored.
4. nCSis pulled back to high.
Figure 7–29. WRDI Operation Sequence
nCS
0
1
2
3
4
5 6 7
SCK
SI
8-bit
Instruction
04H
MSB
High Impedance
SO
MAX V Device Handbook
January 2011 Altera Corporation
INTEL [ INTEL ]
