Renesas M32R/ECU Series, User Manual

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15
15-2
EXTERNAL BUS INTERFACE
32180 Group User’s Manual (Rev.1.0)
15.1 Outline of the External Bus Interface
15.1.1 External Bus Interface Related Signals
The 32180 has the external bus interface related signals described below. These signals can be used in external
extension and processor modes. Furthermore, a dedicated power supply for the bus control pins (bus power
supply: VCC-BUS) is included. When used separately from other power supplies, it allows external devices
operating with other than the main power supply voltage to be connected.
The symbol “#” suffixed to the pin names (or signal names) means that the pins (or signals) are active-low.
(1) Address
The 32180 outputs a 20-bit address (A11–A30) for addressing any location in a 2-Mbyte space. The least
significant A31 is not output.
Note: • During external extension mode, these pins are switched for port after reset. Their pin functions must
be set for address output using the corresponding port operation mode register as necessary.
(2) Chip select (CS0#–CS3#)
The CS0#–CS3# signals are output for extended external areas divided in 2-Mbyte units. The CS0# signal
points to a 2-Mbyte area during processor mode or a 1-Mbyte area during external extension mode. (For
details, see Chapter 3, “Address Space.”)
Note: • During external extension mode, these pins are switched for port after reset. Their pin functions must
be set for chip select using the corresponding Port Operation Mode Register as necessary.
(3) Read strobe (RD#)
Output during an external read cycle, this signal indicates the timing at which to read data from the bus. This
signal is driven high when writing to the bus or accessing the internal area.
(4) Byte High Write/Byte High Enable (BHW#/BHE#)
The pin function changes depending on the Bus Mode Control Register (BUSMODC).
When BUSMOD = "0" and this signal is Byte High Write (BHW#), during external write access it indicates that
the upper byte (DB0–DB7) of the data bus is the valid data transferred. During external read and when
accessing the internal area it outputs a high.
When BUSMOD = "1" and this signal is Byte High Enable (BHE#), during external access (for read or write)
it indicates that the upper byte (DB0–DB7) of the data bus is the valid data transferred. When accessing the
internal area it outputs a high.
(5) Byte Low Write/Byte Low Enable (BLW#/BLE#)
The pin function changes depending on the Bus Mode Control Register (BUSMODC).
When BUSMOD = "0" and this signal is Byte Low Write (BLW#), during external write access it indicates that
the lower byte (DB8–DB15) of the data bus is the valid data transferred. During external read and when
accessing the internal area it outputs a high.
When BUSMOD = "1" and this signal is Byte Low Enable (BLE#), during external access (for read or write) it
indicates that the lower byte (DB8–DB15) of the data bus is the valid data transferred. When accessing the
internal area it outputs a high.
15.1 Outline of the External Bus Interface