II CORE BLOCK: BCU (Bus Control Unit)

RRA1–RRA0: Refresh RAS pulse width selection (D[6:5]) / Bus control register (0x4812E)

Select the RAS pulse width of a CAS-before-RAS refresh.

Table 4.27 Refresh RAS Pulse Width

RRA1

RRA0

Pulse width

1

1

5 cycles

1

0

4 cycles

0

1

3 cycles

0

0

2 cycles

The contents set here are applied to all of areas 14, 13, 8, and 7 that are set for DRAM. The RRA can be read to obtain their set value.

At cold start, RRA is set to "0" (2 cycles). At hot start, RRA retains its status before being initialized.

SBUSST: External interface method select register (D3) / Bus control register (0x4812E)

Select the interface method of an SRAM device.

Write "1": #BSL system

Write "0": A0 system

Read: Valid

When using the #BSL system, write "1" to SBUSST.

The contents set here are applied to all areas that are set for the SRAM type.

At cold start, SBUSST is set to "0" (A0 system). At hot start, SBUSST retains its status before being initialized.

SEMAS: External bus master setup (D2) / Bus control register (0x4812E)

Specify whether an external bus master exists.

Write "1": Existing

Write "0": Nonexistent

Read: Valid

A request for bus ownership control via the #BUSREQ pin is made acceptable by writing "1" to SEMAS. If the system does not have any external bus master, fix this register at "0".

At cold start, SEMAS is set to "0" (nonexistent). At hot start, SEMAS retains its status before being initialized.

SEPD: External power-down control (D1) / Bus control register (0x4812E)

Enable or disable the CPU's power-down control by an external bus master.

Write "1": Enabled

Write "0": Disabled

Read: Valid

Power-down control via an external pin (#BUSREQ) is enabled by writing "1" to SEPD. If the #BUSREQ pin is lowered when external power-down control is thus enabled, the CPU is placed in a HALT state, allowing for reduction in power consumption.

At cold start, SEPD is set to "0" (disabled). At hot start, SEPD retains its status before being initialized.

B-II-4-42

EPSON

S1C33L03 FUNCTION PART