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(1) High-Speed Micro DMA Operation
High-speed micro DMA operation starts when the accepted
interrupt vector value matches the micro DMA start vector
value set in the interrupt controller. The high-speed micro DMA
has four channels so that it can be set for up to four types of
interrupt source.
When a high-speed micro DMA interrupt is accepted,
data is automatically transferred from the transfer source
address to the transfer destination address set in the control
register, and the transfer counter is decremented. If the value in
the counter after decrementing is other than 0, high-speed
micro DMA processing is completed. If the value in the counter
after decrementing is 0, general-purpose interrupt processing
is performed. In read-only mode, which is provided for DRAM
refresh, the value in the counter is ignored and dummy read is
repeated.
The 32-bit control registers are used for setting transfer
source/destination addresses. However, the TLCS-900 has
only 24 address pins for output. A 16M-byte space is available
for the high-speed micro DMA. Also in normal mode operation,
the all address space (in other words, the space for system
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mode which is set by the CS/WAIT controller) can be
accessed by high-speed micro DMA processing.
There are two data transfer modes: one-byte mode and
one-word mode. Incrementing, decrementing, and fixing the
transfer source/destination address after transfer can be done
in both modes. Therefore data can easily be transferred
betweenI/O and memory and between I/Os. For details of
transfer modes, see the description of transfer mode registers.
The transfer counter has 16 bits, so up to 65536 trans-
fers (the maximum when the initial value of the transfer counter
is 0000H) can be performed for one interrupt source by high-
speed micro DMA processing.
A the data transferred by the µ DMA function, the transfer
nter was decreased.
When this counter is "0"H, the processor operates gen-
eral interrupt processing. At this time if the same channel of
interrupt is required next interrupt, the transfer counter starts
from 65536.
Interrupt sources processed by high-speed micro DMA
processing are those with the high-speed micro DMA start
vectors listed in Table 3.3 (1).
TMP96C141AF
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