Mitsubishi Electric M32R Series User Manual page 712

15
15.1 External Bus Interface Related Signals
The 32170 comes with external bus interface related signals shown below. These signals can be
used in external extension mode or processor mode.
(1) Address
The 32170 outputs a 20-bit address (A11-A30) for addressing any location in 2 Mbytes of space.
The least significant A31 is not output, and in external write cycles, the 32170 outputs BHW and
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BLW signals to indicate the valid byte position at which to write on the 16-bit data bus. In read
cycles, the 32170 reads data always in 16 bits, transferring only the data read from the valid byte
position of the bus.
(2) Chip select (CS0, CS1)
These signals are output in external extension mode or processor mode, with CS0 and CS1
specifying an extended external area of 2 Mbytes each. The CS0 signal points to a 2-Mbyte area in
processor mode or a 1-Mbyte area in external extension mode. (For details, refer to Chapter 3,
"Address Space.")
(3) Read strobe (RD)
Output during 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 function.
(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 to transfer. During external
read and when accessing the internal function it outputs a high.
When BUSMOD = 1 and this signal is Byte High Enable (BHE), during external access it indicates
that the upper byte (DB0-DB7) of the data bus is the valid data to transfer. When accessing the
internal function, 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 to transfer. During
external read cycle, it outputs a high.
When BUSMOD = 1 and this signal is Byte Low Enable (BLE), during external access it indicates
that the lower byte (DB8-DB15) of the data bus is the valid data to transfer. When accessing the
internal function, it outputs a high.
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EXTERNAL BUS INTERFACE
15.1 External Bus Interface Related Signals
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