DMA CONTROLLER
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
8 bits
16 bits
8 bits
External
bus width
16 bits
(including
internal
bus)
8 bits
Address directions
Fixed/Forward
Backward
Fixed/Forward/
Backward
Fixed/Forward/
Backward
Fixed/Forward/
Backward
Even
Odd
Even
Odd
Even/Odd
Data’s start
address
Read/Write cycle (Unit:
φ cycle)
Formula
1 + i
2 + i
1 + i
No Wait
2 (a)
3 (b)
2 (a)
With Wait
3 (c)
DRAM area
4 (d)
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.
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 td(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.