Actel Fusion Mixed-Signal FPGAs
Access to the FB is controlled by the BUSY signal. The BUSY output is synchronous to the CLK signal.
FB operations are only accepted in cycles where BUSY is logic 0.
Write Operation
Write operations are initiated with the assertion of the WEN signal. Figure 2-34 on page 2-47
illustrates the multiple Write operations.
CLK
WEN
A0
D0
A1
D1
A2
A3 A4
A5
D5
A6
D6
ADDR[17:0]
WD[31:0]
D2 D3 D4
DATAWIDTH[1:0]
PAGELOSSPROTECT
BUSY
STATUS[1:0]
S0
S1
S2
S3
S4
S5
S6
Figure 2-34 • FB Write Waveform
When a Write operation is initiated to a page that is currently not in the Page Buffer, the FB control
logic will issue a BUSY signal to the user interface while the page is loaded from the FB Array into
the Page Buffer. (Note: The number of clock cycles that the BUSY output is asserted during the load
of the Page Buffer is variable.) After loading the page into the Page Buffer, the addressed data
block is loaded from the Page Buffer into the Block Buffer. Subsequent writes to the same block of
the page will incur no busy cycles. A write to another block in the page will assert BUSY for four
cycles (five cycles when PIPE is asserted), to allow the data to be written to the Page Buffer and
have the current block loaded into the Block Buffer.
Write operations are considered successful as long as the STATUS output is '00'. A non-zero STATUS
indicates that an error was detected during the operation and the write was not performed. Note
that the STATUS output is "sticky"; it is unchanged until another operation is started.
Only one word can be written at a time. Write word width is controlled by the DATAWIDTH bus.
Users are responsible for keeping track of the contents of the Page Buffer and when to program it
to the array. Just like a regular RAM, writing to random addresses is possible. Users can write into
the Page Buffer in any order but will incur additional BUSY cycles. It is not necessary to modify the
entire Page Buffer before saving it to nonvolatile memory.
Write errors include the following:
1. Attempting to write a page that is Overwrite Protected (STATUS = '01'). The write is not
performed.
2. Attempting to write to a page that is not in the Page Buffer when Page Loss Protection is
enabled (STATUS = '11'). The write is not performed.
Program Operation
A Program operation is initiated by asserting the PROGRAM signal on the interface. Program
operations save the contents of the Page Buffer to the FB Array. Due to the technologies inherent
in the FB, a program operation is a time consuming operation (~8 ms). While the FB is writing the
data to the array, the BUSY signal will be asserted.
Preliminary v1.7
2-47
ACTEL [ Actel Corporation ]
