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R8C/26 Group, R8C/27 Group

9. Bus

Rev.2.10

Sep 26, 2008

Page 78 of 453

REJ09B0278-0210

Bus

The bus cycles differ when accessing ROM/RAM, and when accessing SFR.

Table 9.1 lists Bus Cycles by Access Space of the R8C/26 Group and Table 9.2 lists Bus Cycles by Access Space of the

R8C/27 Group.

ROM/RAM and SFR are connected to the CPU by an 8-bit bus. When accessing in word (16-bit) units, these areas are

accessed twice in 8-bit units.

Table 9.3 lists Access Units and Bus Operations.

Table 9.3

Access Units and Bus Operations

However, only following SFRs are connected with the 16-bit bus:

Timer RC: registers TRC, TRCGRA, TRCGRB, TRCGRC, and TRCGRD

Therefore, when accessing in word (16-bit) unit, 16-bit data is accessed at a time. The bus operation is the same as

“Area: SFR, data flash, even address byte access” in Table 9.3 Access Units and Bus Operations, and 16-bit data is

accessed at a time.

Table 9.1

Bus Cycles by Access Space of the R8C/26 Group

Access Area

Bus Cycle

SFR

2 cycles of CPU clock

ROM/RAM

1 cycle of CPU clock

Table 9.2

Bus Cycles by Access Space of the R8C/27 Group

Access Area

Bus Cycle

SFR/Data flash

2 cycles of CPU clock

Program ROM/RAM

1 cycle of CPU clock

Area

SFR, data flash

Even address

Byte access

ROM (program ROM), RAM

Odd address

Byte access

Even address

Word access

Odd address

Word access

CPU clock

Data

Even

Odd

Even+1

Even

Odd+1

Odd

Address

Even+1

Odd+1

Odd

Data

Even

Data

CPU clock

Data

Address

CPU clock

Data

Address

CPU clock

Data

Address

Data

CPU clock

Address

Data

CPU clock

Address

Data

CPU clock

Address

Data

CPU clock

Address

Data

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