Renesas SH7781 - Manual (Page 471)

11. Local Bus State Controller (LBSC)
Rev.1.00 Jan. 10, 2008 Page 441 of 1658
REJ09B0261-0100
11.5.7 Byte Control SRAM Interface
The byte control SRAM interface is a memory interface that outputs a byte-select strobe (
WEn) in
both read and write bus cycles. This interface has 16-bit data pins and can be connected to SRAM
having an upper byte select strobe and lower select strobe functions such as UB and LB.
Areas 1 and 4 can be specified as a byte control SRAM interface.
The write timing for the byte control SRAM interface is identical to that of a normal SRAM
interface.
In reading operation, on the other hand, the
WEn pin timing is different. In a read access, only the
WEn signal for the byte being read is asserted. Assertion is synchronized with the falling edge of
the CLKOUT clock in the same way as for the
WEn signal, while negation is synchronized with
the rising edge of the CLKOUT clock in the same way as for the
RD signal.
In 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 bus is not
released during this transfer.
Figures 11.36 and 11.37 show examples of byte control SRAM connections, and figures 11.38 to
11.40 show examples of byte-control SRAM read cycles.
A17 to A2
CSn
RD
R/ W
SH7785
64K × 16 bits
SRAM
D15 to D0
WE1
WE0
A15 to A0
CS
OE
WE
I/O15 to I/O0
UB
LB
A15 to A0
CS
OE
WE
I/O15 to I/O0
UB
LB
D31 to D16
WE3
WE2
Figure 11.36 Example of Byte Control SRAM with 32-Bit Data Width