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DMA CONT R OLLE R
7721 Group User’s Manual
13-41
13.4 Operation
(2)
Bus operation in 1-bus cycle transfer
The time required for 1-unit transfer in 1-bus cycle transfer is given by the following formulas:
Transfer from memory to I/O: Transfer time per 1-unit transfer = (Read cycle of memory)
Transfer from I/O to memory: Transfer time per 1-unit transfer = (Write cycle of memory)
In 1-bus cycle transfer, 1-transfer-unit data is accessed in 1-bus cycle, so that limitations are imposed
on the transfer conditions to be applied. Table 13.4.5 lists the conditions of 1-bus cycle transfer and
the transfer time per 1-unit transfer, and Figure 13.4.7 shows the bus-cycle operation waveforms in
1-bus cycle transfer.
Table 13.4.5 Conditions of 1-bus cycle transfer and Transfer time per 1-unit transfer
Transfer
unit
16 bits
16 bits
(including
internal
bus)
F i x e d / F o r w a r d /
Backward
F i x e d / F o r w a r d /
Backward
F i x e d / F o r w a r d /
Backward
Address directions: Refer to section
“13.4.2 (3) Address directions in 1-bus cycle transfer.”
There is no address direction on the I/O side.
_
i: A term of
E
= ‘L” in 1-bus cycle; i = 1 at “No Wait”, and i = 2 at “With Wait” or “DRAM area”.
When Ready function is used (Refer to section
“3.3 Ready function.”
), the number of cycles extended
by Ready must be added.
( ): Indicates the corresponding waveform in Figure 13.4.7.
/: 1-bus cycle transfer cannot be performed.
8 bits
16 bits
8 bits
External
bus width
8 bits
Address directions
Fixed/Forward
Backward
Even
Odd
Even
Odd
Even/Odd
Even/Odd
Even/Odd
Data’s start
address
Read/Write cycle (Unit:
φ
cycle)
Formula
1 + i
2 (a)
2 + i
1 + i
1 + i
No Wait
3 (b)
2 (a)
2 (a)
With Wait
3 (c)
3 (c)
3 (c)
DRAM area
4 (d)
When the external data bus width = 16 bits and the transfer unit = 8 bits are selected, the data bus
which the memory uses and the data bus to which I/O is connected may be different. In such a case,
data is copied from the data bus of a transfer source to that of a transfer destination by using the
DMA latch. For the combination that data copy may occur, data copy delay time t
d(data)
must be taken
into consideration.
Table 13.4.6 lists the data flows on the data bus in 1-bus cycle transfer, and Table 13.4.7 lists the
outputs of the address bus, the data bus, and the bus control signals in 1-bus cycle transfer.