DMA Timers (DTIM0–DTIM3)
24-8
Freescale Semiconductor
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
24.2.6
DMA Timer Counters (DTCNn)
The current value of the 32-bit timer counter can be read at anytime without affecting counting. Writes to
DTCN
n
clear the timer counter. The timer counter increments on the clock source rising edge (internal bus
clock divided by 1, internal bus clock divided by 16, or DTIN
n
).
24.3
Functional Description
24.3.1
Prescaler
The prescaler clock input is selected from the internal bus clock (f
sys
divided by 1 or 16) or from the
corresponding timer input, DTIN
n
. DTIN
n
is synchronized to the internal bus clock, and the
synchronization delay is between two and three internal bus clocks. The corresponding DTMR
n
[CLK]
selects the clock input source. A programmable prescaler divides the clock input by values from 1 to 256.
The prescaler output is an input to the 32-bit counter, DTCN
n
.
24.3.2
Capture Mode
Each DMA timer has a 32-bit timer capture register (DTCR
n
) that latches the counter value when the
corresponding input capture edge detector senses a defined DTIN
n
transition. The capture edge bits
(DTMR
n
[CE]) select the type of transition that triggers the capture and sets the timer event register capture
event bit, DTER
n
[CAP]. If DTER
n
[CAP] and DTXMR
n
[DMAEN] are set, a DMA request is asserted. If
DTER
n
[CAP] is set and DTXMR
n
[DMAEN] is cleared, an interrupt is asserted.
24.3.3
Reference Compare
Each DMA timer can be configured to count up to a reference value. If the reference value is met,
DTER
n
[REF] is set.
•
If DTMR
n
[ORRI] is set and DTXMR
n
[DMAEN] is cleared, an interrupt is asserted.
•
If DTMR
n
[ORRI] and DTXMR
n
[DMAEN] are set, a DMA request is asserted.
IPSBAR
Offset:
0x00_040C
(
DTCN0
)
0x00_044C
(
DTCN1
)
0x00_048C
(
DTCN2
)
0x00_04CC
(
DTCN3
)
Access: User read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R
CNT (32-bit timer counter value count)
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Figure 24-7. DMA Timer Counters (DTCNn)
Table 24-7. DTCNn Field Descriptions
Field
Description
31–0
CNT
Timer counter. Can be read at anytime without affecting counting and any write to this field clears it.
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
