60
XMEGA B [DATASHEET]
8291B–AVR–01/2013
Note:
1.
CC channel C and D triggers are available only for timer/counters 0.
The group configuration is the “base_offset;” for example, TCC1_CCA for the timer/counter C1 CC channel A the transfer
trigger.
5.14.5 TRFCNTL – Channel Block Transfer Count register Low
The TRFCNTH and TRFCNTL register pair represents the 16-bit value TRFCNT. TRFCNT defines the number of bytes
in a block transfer. The value of TRFCNT is decremented after each byte read by the DMA channel. When TRFCNT
reaches zero, the register is reloaded with the last value written to it.
Bit 7:0 – TRFCNT[7:0]: Channel n Block Transfer Count low byte
These bits hold the LSB of the 16-bit block transfer count.
The default value of this register is 0x1. If a user writes 0x0 to this register and fires a DMA trigger, DMA will be doing
0xFFFF transfers.
Table 5-9.
DMA trigger source offset values for event system triggers.
TRGSRC Offset Value
Group Configuration
Description
+0x00
CH0
Event channel 0
+0x01
CH1
Event channel 1
+0x02
CH2
Event channel 2
Table 5-10. DMA trigger source offset values for timer/ counter triggers.
TRGSRC Offset Value
Group Configuration
Description
+0x00
OVF
Overflow/underflow
+0x01
ERR
Error
+0x02
CCA
Compare or capture channel A
+0x03
CCB
Compare or capture channel B
+0x04
CCC
Compare or capture channel C
+0x05
CCD
Compare or capture channel D
Table 5-11.
DMA trigger source offset values for USART triggers.
TRGSRC Offset Value
Group Configuration
Description
0x00
RXC
Receive complete
0x01
DRE
Data register empty
Bit
7
6
5
4
3
2
1
0
TRFCNT[7:0]
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Содержание XMEGA B
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