Table 10.14 Example of Correspondence between SH7709S and Synchronous DRAM
Address Pins (AMX [3:0] = 0100 (32-Bit Bus Width))
SH7709S Address Pin
RAS Cycle
A23
Synchronous DRAM Address Pin
Function
CAS Cycle
A23
A22
A13
L/H
A11
A10
A9
A15
A14
A13
A12
A11
A10
A9
A13(BA1)
A12(BA0)
A11
BANK select bank address
A22
A21
A20
A19
A18
A17
A16
A15
A14
A13
A12
A11
A10
A9
Address
A10
Address precharge setting
Address
A9
A8
A7
A8
A8
A6
A7
A7
A5
A6
A6
A4
A5
A5
A3
A4
A4
A2
A3
A3
A1
A2
A2
A0
A1
A1
Not used
Not used
A0
A0
A0
Burst Read: In the example in figure 10.15 it is assumed that four 2M × 8-bit synchronous
DRAMs are connected and a 32-bit data width is used, and the burst length is 1. Following the Tr
cycle in which ACTV command output is performed, a READ command is issued in the Tc1, Tc2,
and Tc3 cycles, and a READA command in the Tc4 cycle, and the read data is accepted at the
rising edge of the external command clock (CKIO) from cycle Td1 to cycle Td4. The Tpc cycle is
used to wait for completion of auto-precharge based on the READA command inside the
synchronous DRAM; no new access command can be issued to the same bank during this cycle,
but access to synchronous DRAM for another area is possible. In the SH7709S, the number of Tpc
cycles is determined by the TPC bit specification in MCR, and commands cannot be issued for the
same synchronous DRAM during this interval.
The example in figure 10.14 shows the basic cycle. To connect low-speed synchronous DRAM,
the cycle can be extended by setting WCR2 and MCR bits. The number of cycles from the ACTV
command output cycle, Tr, to the READ command output cycle, Tc1, can be specified by the
RCD bits in MCR, with values of 0 to 3 specifying 1 to 4 cycles, respectively. In case of 2 or more
cycles, a Trw cycle, in which an NOP command is issued for the synchronous DRAM, is inserted
between the Tr cycle and the Tc cycle. The number of cycles from READ and READA command
output cycles Tc1-Tc4 to the first read data latch cycle, Td1, can be specified as 1 to 3 cycles
Rev. 5.00, 09/03, page 281 of 760
RENESAS [ RENESAS TECHNOLOGY CORP ]
