7721 Group User’s Manual
13-20
DMA CONTROLLER
13.3 Control
13.3.2 DMA requests
(1)
DMA request sources
DMA request sources are specified by the DMA request source select bits and the edge sense/level
sense select bit. (Refer to “Figure 13.2.8.”)
Table 13.3.2 lists the conditions for generating a DMA request.
Table 13.3.2 Conditions for generating DMA request
DMA request sources
Condition for generating DMA request
Level sense
Edge sense
External source
________
DMAREQi
Software DMAi request
Timers A0–A4,
Timers B0–B2,
UART0, UART1,
A-D converter
_________
“L”-level input to the DMAREQi pin (only in the burst transfer mode)
_________
Change of the DMAREQi input pin’s level from “H” to “L”
A write of “1” to the software DMAi request bit (each of bits 0–3 at address 6916;
refer to “Figure 13.2.5.”)
When the interrupt request bit of each peripheral is set to “1” by the activity of
peripherals (If “1” is written to any of these interrupt request bits by software,
the DMAi request bit does not change. Also, whatever value within 0–7 an
interrupt priority level takes, this does not affect DMA requests.)
(2)
Change of DMAi request bit
A read of the DMAi request bits (each of bits 4–7 at address 6816) indicates whether the corresponding
channel (0–3) is generating its DMA request or not. The DMAi request bit changes synchronized with
the falling edge of
φ1. Table 13.3.3 lists the conditions for changing the DMAi request bit.
For the timing of changing the DMAi request bit, refer to “Figures 13.3.2 and 13.3.3.”
Table 13.3.3 Conditions for changing DMAi request bit
DMAi
request bit
Mode
Is set to “1.”
(Note)
Is cleared to “0.”
Generation of DMAi request
(Refer to “Table 13.3.2.”)
Generation of DMAi request
(“L”-level
input
to
the
_________
DMAREQi
pin)
Generation of DMAi request
(Refer to “Table 13.3.2.”)
Normal termination
___
level from “H ”to “L” during
___
DMA transfer (when the TC
pin is valid)
“H”-level input to the
_________
DMAREQi pin
___
Change of the TC pin’s input
level from “H” to “L” (when
___
the TC pin is valid)
A write of “0” to the DMAi
request bit
A write of “0” to the DMAi
enable bit
Start of 1-unit transfer
___
Change of the TC pin’s input
level from “H” to “L” during
___
DMA transfer (when the TC
pin is valid)
A write of “0” to the DMAi
request bit
A write of “0” to the DMAi
enable bit
Cycle-steal transfer mode
Burst transfer mode
Edge sense
Level sense
Note: While the DMAi enable bit is “0,” the DMAi request bit is not set to “1” even if a DMA request is
generated. When the DMAi enable bit is cleared to “0,” also the DMAi request bit is cleared to “0.”
However, the DMA request generated while the DMAi enable bit = “0” is maintained; and when the
DMAi enable bit is set to “1,” the DMAi request bit is also set to “1,” except for the burst transfer mode
(level sense).