RS_Flexible static memory controller (FSMC)
RM0082
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Doc ID 018672 Rev 1
by accessing particular regions of the common memory space we can send to the
NAND Flash a command (CLE high) or an address (ALE high).
●
Attribute memory space access.
The only difference with respect to previous
common memory access mode is that the timings used are specified in the register
GenMemCtrl_Attrib. In practice, this secondary access works exactly the same as
common memory space accesses, but this can be used to implement a functionality
that is needed in some (but not all) NAND Flash memories. Some Flash memories
require that after writing the last part of the address, the controller has to wait and
check that R/B (the wait signal from the Flash) goes low. This pre-wait time can be up
to 100ns, then if there is such event the controller has to wait again until R/B goes high.
During all this period, CE must be held low. Other NAND Flash memories (such as the
Samsung 1 Gbit) do not require the pre-wait time; they just require that when the
memory is being accessed and R/B is low, the controller should wait until R/B goes
high.
31.3.3
Asynchronous SRAM and NOR parallel Flash controller
This block interfaces the AHB Interface block to external memory devices, such as SRAM
and NOR Flash. All memories share the same signals (address, data and control) except
chip select, that is unique for each controlled memory, with the following exceptions:
●
SRAMs use also the byte lane (BL) to specify the byte to read or write, while NOR
Flash has no such input;
●
NOR Flash have address valid signal (ADV)
Note:
Byte Lane and address valid signal have not been made available on SPEAr300 ports. So
SRAMs which require BL inputs cannot be connected. Also, NOR Flash memories requiring
ADV input cannot be connected.
●
Address and control signals are automatically driven by this controller according to the
type of memory in use.
Note:
Synchronous memory access cannot be implemented in SPEAr300 due to non-availability
of port to issue clock to the memory.
31.4 Programming
model
31.4.1 External
signals
Table 592.
Parallel NOR flash
Signal
Direction
Description
DQ15:0
Bidir
Data lines.
A23:0
Out
Address lines.
/W
Out
Write Enable Active Low.
/R
Out
Read Enable Active Low.
/E1, /E2, /E3 and /E4
Out
Chip Enable Active Low.
R/B
In
Wait Signal Active Low.