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Bus Controller (BC)
8.13.12 8-bit Bus in Asynchronous Mode and in Address/Data Multiplex Mode
By setting the mode through the MMOD1 and 0 pins and the EXMOD1 and 0 pins, blocks 0 to 3 use multiplex pins
for the memory address and memory data signals (pins ADM15 to 0).
8-bit bus mode is set for block 0 by setting the mode through the MMOD1 and 0 pins and the EXMOD1 and 0 pins,
and for blocks 1 to 3 by setting the BnBW bit to "0" in the corresponding memory control register. In 8-bit bus
mode, half-word access (16 bits) is performed by means of two external accesses, with A[0] = "0" for the low-order
byte and A[0] = "1" for the high-order byte. Word access (32 bits) is performed by means of four accesses, with
A[1:0] = "00", A[1:0] = "01", A[1:0] = "10", and A[1:0] = "11", starting from the low-order side. Note that the
low-order 8 bits (D7 to 0) are used for the data bus.
Asynchronous mode is used for accessing external memory at high speed; the address signals, CSn signals, etc., are
output asynchronously with SYSCLK but in synchronization with the internal MCLK. In asynchronous mode,
accesses are all by fixed wait insertion.
The various parameters for external memory access are set in memory control registers 0 to 3, corresponding to
each block.
Fig. 8-13-30 is the timing chart in the case of a half-word access using an "8-bit bus in asynchronous mode, in
address/data multiplex mode."
As shown in each timing chart, the ADM15 to 0 pins go to "Hi-Z" or the undefined output state while CSn is
negated in address/data multiplex mode. When the bus authority is released, the ADM15 to 0 pins are either pulled
up or go to "Hi-Z", depending on the setting of the I/O port output mode register.
Note that when writing, WE0 is asserted and the data is output on ADM7 to 0.
Note: For details on the mode settings, refer to Table 8-9-1, "Mode Settings by the BC External Pins."
Note: "0" (low level) is output on pins A23 to 16 (A23 also serves as CS3) while the ADM15 to 0 pins function as
data pins. Therefore, refer to 3. in section 8.16, "Cautions," regarding the use of these pins.
8-60
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