M30621ECGP MITSUBISHI [Mitsubishi Electric Semiconductor], M30621ECGP Datasheet - Page 63

• Manufacturer Part Number: M30621ECGP
• Description: SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
• Manufacturer: MITSUBISHI [Mitsubishi Electric Semiconductor]

DMAC
(1) Transfer cycle
The transfer cycle consists of the bus cycle in which data is read from memory or from the SFR area
(source read) and the bus cycle in which the data is written to memory or to the SFR area (destination
write). The number of read and write bus cycles depends on the source and destination addresses. In
memory expansion mode and microprocessor mode, the number of read and write bus cycles also de-
pends on the level of the BYTE pin. Also, the bus cycle itself is longer when software waits are inserted.
Figure 1.12.5 shows the example of the transfer cycles for a source read. For convenience, the destina-
tion write cycle is shown as one cycle and the source read cycles for the different conditions are shown.
In reality, the destination write cycle is subject to the same conditions as the source read cycle, with the
transfer cycle changing accordingly. When calculating the transfer cycle, remember to apply the respec-
tive conditions to both the destination write cycle and the source read cycle. For example (2) in Figure
1.12.5, if data is being transferred in 16-bit units on an 8-bit bus, two bus cycles are required for both the
source read cycle and the destination write cycle.
(a) Effect of source and destination addresses
(b) Effect of software wait
When 16-bit data is transferred on a 16-bit data bus, and the source and destination both start at odd
addresses, there are one more source read cycle and destination write cycle than when the source
and destination both start at even addresses.
When the SFR area or a memory area with a software wait is accessed, the number of cycles is
increased for the wait by 1 bus cycle. The length of the cycle is determined by BCLK.
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
M16C / 62 Group (80-pin)
Mitsubishi microcomputers
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