Device Architecture
Read Next Operation
The Read Next operation is a feature by which the next block relative to the block in the Block
Buffer is read from the FB Array while performing reads from the Block Buffer. The goal is to
minimize wait states during consecutive sequential Read operations.
The Read Next operation is performed in a predetermined manner because it does look-ahead
reads. The general look-ahead function is as follows:
•
•
•
•
•
Within a page, the next block fetched will be the next in linear address.
When reading the last data block of a page, it will fetch the first block of the next page.
When reading spare pages, it will read the first block of the next sector's spare page.
Reads of the last sector will wrap around to sector 0.
Reads of Auxiliary blocks will read the next linear page's Auxiliary block.
When an address on the ADDR input does not agree with the predetermined look-ahead address,
there is a time penalty for this access. The FB will be busy finishing the current look-ahead read
before it can start the next read. The worst case is a total of nine BUSY cycles before data is
delivered.
The Non-Pipe Mode and Pipe Mode waveforms for Read Next operations are illustrated in
Figure 2-39 and Figure 2-40.
CLK
REN
READNEXT
ADDR[17:0]
DATAWIDTH[1:0]
BUSY
A0
A1
A2
A3
A4
A5
S4
A6
A7
A8
A9
STATUS[1:0]
RD[31:0]
0
0
S0
S1
S2
S3
0
0
S5
S6
S7
0
0
S8 S9
D8 D9
D0 D1 D2 D3
D4 D5 D6 D7
Figure 2-39 • Read Next Waveform (Non-Pipe Mode, 32-bit access)
CLK
REN
READNEXT
A0
A1
A2
A3
A4
A5
A6
A7
A8
ADDR[17:0]
BUSY
S0
S1
D1
S2
D2
S3
D3
0
0
S4
D4
S5
D5
S6
D6
S7
0
0
STATUS[1:0]
RD[31:0]
0
D0
D7
Figure 2-40 • Read Next WaveForm (Pipe Mode, 32-bit access)
2-52
Preliminary v1.7
ACTEL [ Actel Corporation ]
