M16C26 Datasheet, PDF (77/239 Pages) Renesas Technology Corp – 16-BIT CMOS SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/20 SERIES

Udenvdeelropment
DMAC
Preliminary Specifications Rev. 0.9
Specifications in this manual are tentative and subject to change.
M16C/26 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
(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. Also,
the bus cycle itself is longer when software waits are inserted.
(a) Effect of source and destination addresses
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.
(b) Effect of software wait
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.
Figure 1.11.5 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
1.11.5, if 16-bit data is being transferred from an odd source address to an odd destination address, two
bus cycles are required for both the source read cycle and the destination write cycle.
(2) DMAC transfer cycles
Any combination of even or odd transfer read and write addresses is possible. Table 1.11.2 shows the
number of DMAC transfer cycles.
The number of DMAC transfer cycles can be calculated as follows:
No. of transfer cycles per transfer unit = No. of read cycles x j + No. of write cycles x k
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