SH7708 datasheet(232/633 Pages) RENESAS

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214

10.2.6

DRAM Control Register (DCR)

The DRAM area control register (DCR) is a 16-bit read/write register that specifies

RAS and CAS

timing and burst control for DRAM connected to area 2. It also specifies address multiplexing and

controls refreshing. When DRAM is connected to area 2, the bus width is fixed at 16 bits. In such

cases, set the area 3 bus width to 16 bits as well. Other areas should be 8 bits or 16 bits. DCR is

initialized to H'0000 by a power-on reset, but is not initialized by a manual resets or in standby

mode. Do not access external memory outside area 2 until initialization of this register is

complete.

Bit:

Bit name:

TPC1

TPC0

RCD1

RCD0

—

TRAS1

TRAS0

Initial value:

R/W:

R/W

Bit:

Bit name:

—

AMX1

AMX0

RFSH

RMODE

—

Initial value:

R/W:

R/W

Bits 15 and 14—RAS Precharge Time (TPC1, TPC0): These bits set the RAS precharge time for

the DRAM connected to area 2.

Description

Bit 15: TPC1

Bit 14: TPC0

Normally

Immediately after Self-Refresh

1 cycle (Initial value)

2 cycles (Initial value)

2 cycles

5 cycles

3 cycles

8 cycles

4 cycles

11 cycles

Bits 13 and 12—RAS–CAS Delay (RCD1, RCD0): These bits set the RAS–CAS delay time for

the DRAM connected to area 2.

Bit 13: RCD1

Bit 12: RCD0

Description

1 cycle

(Initial value)

2 cycles

3 cycles

4 cycles

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