External Bus; External Bus Mode - Renesas M16C/64A Series User Manual

M16C/64A Group
11.3.3

External Bus

The external bus is used to access external devices in memory expansion mode or microprocessor
mode.
In memory expansion or microprocessor mode, some pins serve as the bus control pins to perform data
input to and output from external devices. The bus control pins are as follows: A0 to A19, D0 to D15,
CS0 to CS3 , RD, WRL / WR , WRH / BHE , ALE, RDY , HOLD , HLDA , and BCLK.
11.3.4

External Bus Mode

Multiplexed bus mode or separate bus mode can be selected using bits PM05 to PM04 in the PM0
register. Table 11.4 lists the Difference between Separate Bus and Multiplexed Bus Modes.
11.3.4.1 Separate Bus
In external bus mode, data and address are separate.
11.3.4.2 Multiplexed Bus
In external bus mode, data and address are multiplexed.
•
When the input level to the BYTE pin is high (8-bit data bus)
D0 to D7 and A0 to A7 are multiplexed.
•
When the input level to the BYTE pin is low (16-bit data bus)
D0 to D7 and A1 to A8 are multiplexed. D8 to D15 are not multiplexed (do not use these pins).
External devices connected to a multiplexed bus are assigned only even addresses of the MCU.
Table 11.4 Difference between Separate Bus and Multiplexed Bus Modes
(1)
Pin Name
P0_0 to P0_7/D0 to D7
P1_0 to P1_7/D8 to D15
P2_0/A0 (/D0)
P2_1 to P2_7/A1 to A7
(/D1 to D7/D0 to D6)
P3_0/A8 (/D7)
Notes:
1. See Table 11.8 "Pin Functions for Each Processor Mode" for bus control signals not listed above.
2. Depends on the setting of bits PM05 to PM04 in the PM0 register, and area being accessed.
See Table 11.8 "Pin Functions for Each Processor Mode" for details.
R01UH0136EJ0210 Rev.2.10
Jul 31, 2012
Separate Bus
D0 to D7
D8 to D15
A0
A1 to A7
A1 to A7 D1 to D7
A8
Multiplexed Bus
BYTE = high
(Note 2)
I/O port
P1_0 to P1_7
D0
A0
A1 to A7 D0 to D6
A8
11. Bus
BYTE = low
(Note 2)
(Note 2)
A0
D7
A8
Page 143 of 800