7641 datasheet(258/385 Pages) RENESAS

258 / 385 page

Rev.2.00

Aug 28, 2006

page 127 of 148

7641 Group

REJ09B0336-0200

APPLICATION

2.10 External devices connection

2.10.6 Expanded data memory access

In Expanded Data Memory Access Mode (EDMA mode), the MCU can access a data area larger than 64

Kbytes with the LDA ($zz), Y (indirect Y) instruction and the STA ($zz), Y (indirect Y) instruction. It is only

able to store and read data for the expanded data memory area. The access can be performed with T flag

= “0” or “1”. (T flag is Index X mode flag.)

To use this mode, set the expanded data memory access bit (b4 of CPMB) to “1”. In this case, EDMA pin

(port P40) goes “L” level during the read/write cycle of the LDA or STA instruction. The determination of

which bank to access is done by using an I/O port to represent expanded addresses exceeding address

bus (AB15)16. This signal and the port output signal are put together, and it becomes the chip select

(selecting a bank, expanded memory).

In EDMA mode, the area from addresses 000016 to FFFF16 can be accessed. When accessing a bank,

follow this procedure (four banks are assumed):

- Bank specification (Data output to the port for a bank setup 16 (AB16), and 16 (AB17)). The user must

setup 16 (AB16), and 16 (AB17).

__________

- Enabling EDMA output. (Set b4 of CPMB to “1”.)

- Executing LDA ($zz), Y (indirect Y) (In the case of read data of expanded data memory)

The data of the address (bank 0) + Y stored in the internal RAM address ($zz) are loaded to the accumulator.

Figure 2.10.8 shows a connection example of memory access up to 256 Kbytes.

EDMA

CS0

CS1

CS2

CS3

DB0 to DB7

P80

P81

AB0 to AB15

BANK0

BANK1

BANK2

BANK3

74HC139

7641 group

Decoder

64K RAM

Fig. 2.10.8 Connection example of memory access up to 256 Kbytes

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