M32C83T datasheet(75/527 Pages) RENESAS

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7. Bus

)

(

7. Bus

In memory expansion mode or microprocessor mode, some pins function as bus control pins to input and

______

_______

________ ______ _________

output data from external devices. A0 to A22, A23, D0 to D15, MA0 to MA12, CS0 to CS3, WRL/WR/CASL,

_________ _______ __________

_____ ______

_________

_______

WRH/BHE/CASH, RD/DW, BCLK/ALE, HLDA/ALE, HOLD, ALE/RAS, and RDY are used as bus control

pins.

Bus control pins in M32C/83T cannot be used.

Figure 7.1 DS Register

NOTES:

1. After reset, the DS3 bit is set to "1" when the BYTE pin is held "L". It is set to "0" when the BYTE pin

is held "H".

2. The DS register in the M32C/83T cannot be used.

Symbol

Address

After Reset

000B16

XXXX 10002 (BYTE pin = "L")

XXXX 00002 (BYTE pin = "H")

External Data Bus Width Control Register(2)

DS0

DS1

DS2

DS3

(b7 - b4)

0 : 8 bits wide

1 : 16 bits wide

0 : 8 bits wide

1 : 16 bits wide

0 : 8 bits wide

1 : 16 bits wide

0 : 8 bits wide

1 : 16 bits wide

Bit Name

Function

Bit

Symbol

Nothing is assigned. When write, set to "0".

When read, its content is indeterminate.

External Space 0 Data

Bus Width Select Bit

External Space 1 Data

Bus Width Select Bit

External Space 2 Data

Bus Width Select Bit

External Space 3 Data

Bus Width Select Bit(1)

7.1 Bus Settings

The BYTE pin, the DS register, the PM05 to PM04 bits in the PM0 register and the PM11 to PM10 bits in

the PM1 register determine bus settings.

Table 7.1 lists how to change a bus setting. Figure 7.1 shows the DS register.

Table 7.1 Bus Settings

Bus Setting

Changed By

Selecting external address bus width

DS register

Setting bus width after reset

BYTE pin (external space 3 only)

Switching between separate bus or multiplexed bus

PM05 to PM04 bits in PM0 register

Number of chip-select

PM11 to PM10 bits in PM1 register

NOTE

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