HD64F2149YV datasheet(173/1075 Pages) RENESAS

173 / 1075 page

Section 6 Bus Controller

Rev. 3.00 Jan 18, 2006 page 145 of 1044

REJ09B0280-0300

Bits 1 and 0—Wait Count 1 and 0 (WC1, WC0): These bits select the number of program wait

states when external memory space is accessed while the AST bit is set to 1.

Bit 1

Bit 0

WC1

WC0

Description

No program wait states are inserted

1 program wait state is inserted in external memory space accesses

2 program wait states are inserted in external memory space accesses

3 program wait states are inserted in external memory space accesses

(Initial value)

6.3

Overview of Bus Control

6.3.1

Bus Specifications

The external space bus specifications consist of three elements: bus width, number of access

states, and wait mode and number of program wait states.

The bus width and number of access states for on-chip memory and internal I/O registers are

fixed, and are not affected by the bus controller.

Bus Width: A bus width of 8 or 16 bits can be selected with the ABW bit.

Number of Access States: Two or three access states can be selected with the AST bit.

When 2-state access space is designated, wait insertion is disabled. The number of access states on

the burst ROM interface is determined without regard to the AST bit setting.

Wait Mode and Number of Program Wait States: When 3-state access space is designated by

the AST bit, the wait mode and the number of program wait states to be inserted automatically is

selected with WMS1, WMS0, WC1, and WC0. From 0 to 3 program wait states can be selected.

Table 6.3 shows the bus specifications for each basic bus interface area.

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