SH7763 Datasheet, PDF (465/2026 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC Engine Family SH-4A Series

Section 11 Local Bus State Controller (LBSC)
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. However, when these areas are
set to the MPX interface, the MPX interface has priority.
The write timing for the byte control SRAM interface is identical to that of a normal SRAM
interface.
In read operations, on the other hand, the WEn pin timing is different. In a read access, only the
WE 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 WE 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 wrap around method according to the set bus width. The bus is not
released during this transfer.
Figure 11.37 shows an example of a byte control SRAM connection, and figures 11.38 to 11.40
show examples of byte-control SRAM read cycles.
This LSI
A18 to A3
CSn
RD
RDWR
D31 to D16
WE3
WE2
D15 to D0
WE1
WE0
64K × 16-bit
SRAM
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
Figure 11.34 Example of 32-Bit Data-Width Byte-Control SRAM
Rev. 1.00 Oct. 01, 2007 Page 399 of 1956
REJ09B0256-0100