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FlashROM in Actel’s Low-Power Flash Devices
5 – FlashROM in Actel’s Low-Power Flash Devices
Introduction
The IGLOO, ProASIC3, and Fusion families of low-power flash-based FPGAs have a dedicated
nonvolatile FlashROM memory of 1,024 bits, which provides a unique feature in the FPGA market.
The FlashROM can be read, modified, and written using the JTAG (or UJTAG) interface. It can be
read but not modified from the FPGA core. Only low-power flash FPGAs contain on-chip user
nonvolatile memory (NVM).
Architecture of User Nonvolatile FlashROM
Low-power flash devices have 1 kbit of user-accessible nonvolatile flash memory on-chip that can
be read from the FPGA core fabric. The FlashROM is arranged in eight banks of 128 bits (16 bytes)
during programming. The 128 bits in each bank are addressable as 16 bytes during the read-back
of the FlashROM from the FPGA core.
Figure 5-1 shows the FlashROM logical structure.
The FlashROM can only be programmed via the IEEE 1532 JTAG port. It cannot be programmed
directly from the FPGA core. When programming, each of the eight 128-bit banks can be selectively
reprogrammed. The FlashROM can only be reprogrammed on a bank boundary. Programming
involves an automatic, on-chip bank erase prior to reprogramming the bank. The FlashROM
supports synchronous read. The address is latched on the rising edge of the clock, and the new
output data is stable after the falling edge of the same clock cycle. For more information, refer to
the timing diagrams in the appropriate family datasheet DC and Switching Characteristics chapter.
The FlashROM can be read on byte boundaries. The upper three bits of the FlashROM address from
the FPGA core define the bank being accessed. The lower four bits of the FlashROM address from
the FPGA core define which of the 16 bytes in the bank is being accessed.
Figure 5-1 FlashROM Architecture
Bank
Number
3
MSB
of
ADDR
(READ)
Byte Number in Bank
4 LSB of ADDR (READ)
7
0
1
2
3
4
5
6
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15