Section 11 Local Bus State Controller (LBSC)
Rev.1.00 Dec. 13, 2005 Page 370 of 1286
REJ09B0158-0100
11.5.4
Burst ROM (Clock Asynchronous) Interface
Setting the TYPE bit in CSnBCR (n = 0 to 2 and 4 to 6) to 010 allows a burst ROM (clock
asynchronous memory) to be connected to areas 0 to 2 and 4 to 6. The burst ROM interface
provides high-speed access to ROM that has a burst access function. The burst access timing of
burst ROM is shown in figure 11.11. The wait cycle is set to 0 cycle. Although the access is
similar to that of the SRAM interface, only the address is changed when the first cycle ends and
then the next access is started. When 8-bit ROM is used, the number of consecutive accesses can
be set as 4, 8, 16, or 32 through bits BST2 to BST0 in CSnBCR (n = 0 to 2 and 4 to 6). Similarly,
when 16-bit ROM is used, 4, 8 or 16 accesses can be set; when 32-bit ROM is used, 4 or 8
accesses can be set.
The
RDY
signal is always sampled when one or more wait cycles are set.
Even when no wait is specified in the burst ROM settings, two access cycles are inserted in the
second and subsequent accesses as shown in figure 11.12.
A writing operation for this interface is performed in the same way as for the SRAM interface.
In a 32-byte transfer, a total of 32 bytes are transferred continuously according to the set bus
width. The first access is performed on the data for which there was an access request, and the
remaining accesses are performed in wraparound method according to the set bus width. The burst
access is stopped once (negate the
RD
) at the address boundary which is a bus width
(CSnBCR.SZ) x burst length (CSnBCR.BST) address and then the access is resumed by the
settings of CSnWCR. The bus is not released during this transfer.
Figure 11.13 shows the timing chart when the burst ROM is used and setup/hold is specified by
CSnWCR.
Содержание SH7780 Series
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Страница 492: ...Section 12 DDR SDRAM Interface DDRIF Rev 1 00 Dec 13 2005 Page 442 of 1286 REJ09B0158 0100 ...
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