R01UH0092EJ0110 Rev.1.10
Page 144 of 807
Jul 31, 2012
M16C/64C Group
11. Bus
11.3.5
External Bus Control
The following describes the signals needed for accessing external devices and the functionality of
software wait states.
11.3.5.1
Address Bus
The address bus consists of 20 lines: A0 to A19. The address bus width can be set to 12, 16, or 20
bits using the PM06 bit in the PM0 register, and the PM11 bit in the PM1 register. Table 11.5 lists the
Set Value of Bits PM06 and PM11 and the Corresponding Address Bus Widths.
When the processor mode is changed from single-chip mode to memory expansion mode, the
address bus is undefined until an external area is accessed.
11.3.5.2
Data Bus
When input to the BYTE pin is high (8-bit width), the data bus is comprised of eight lines (D0 to D7).
When input to the BYTE pin is low (16-bit width), the data bus is comprised of 16 lines (D0 to D15).
Do not change the input level to the BYTE pin.
11.3.5.3
Chip Select Signal
The chip select signals (hereafter referred to as
CS
) are output from the
CSi
pin (i = 0 to 3). These
pins can be set to function as I/O ports or as
CS
using the CSi bit in the CSR register.
In 1-MB mode, the external area can be separated into a maximum of four spaces by the
CSi
signal.
In 4-MB mode, the
CSi
signal or bank number is output from the
CSi
pin. Refer to 12. “Memory Space
Expansion Function”. Figure 11.2 shows Examples of Address Bus and
CSi
Signal Output in 1-MB
Mode.
Table 11.5
Set Value of Bits PM06 and PM11 and the Corresponding Address Bus Widths
Bit Set Value
(1)
Pin Function
Address Bus Width
PM11 = 1
P3_4 to P3_7
12 bits
PM06 = 1
P4_0 to P4_3
PM11 = 0
A12 to A15
16 bits
PM06 = 1
P4_0 to P4_3
PM11 = 0
A12 to A15
20 bits
PM06 = 0
A16 to A19
Note:
1.
Only set the values listed above.
Содержание M16C Series
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