Filter
Top Products
45 www.national.com
CP3BT26
9.6.6 Block Length Register (BLTRn)
The Block Length register is a 16-bit, read/write register. It
holds the number of DMA transfers to be performed for the
next block. Writing this register automatically sets the DM-
ASTAT.VLD bit.
Note: 0000h is interpreted as 2
16
-1 transfer cycles.
9.6.7 DMA Control Register (DMACNTLn)
The DMA Control register n is a word-wide, read/write reg-
ister that controls the operation of DMA channel n. This reg-
ister is cleared at reset. Reserved bits must be written with
0.
CHEN The Channel Enable bit must be set to enable
any DMA operation on this channel. Writing a
1 to this bit starts a new DMA transfer even if
it is currently a 1. If all DMACNTLn.CHEN bits
are clear, the DMA clock is disabled to reduce
power.
0
– Channel disabled.
1 – Channel enabled.
ETC If the Enable Interrupt on Terminal Count bit is
set, it enables an interrupt when the DMAS-
TAT.TC bit is set.
0
– Interrupt disabled.
1
– Interrupt enabled.
EOVR If the Enable Interrupt on OVR bit is set, it en-
ables an interrupt when the DMASTAT.OVR
bit is set.
0
– Interrupt disabled.
1
– Interrupt enabled.
TCS The Transfer Cycle Size bit specifies the num-
ber of bytes transferred in each DMA transfer
cycle. In direct (fly-by) mode, undefined re-
sults occur if the TCS bit is not equal to the ad-
dressed memory bus width.
0
– Byte transfers (8 bits per cycle).
1
– Word transfers (16 bits per cycle).
IND The Direct/Indirect Transfer bit specifies the
transfer type.
0
– Direct transfer (flyby).
1
– Indirect transfer (memory-to-memory).
DIR The Transfer Direction bit specifies the direc-
tion of the transfer relative to Device A.
0
– Device A (pointed to by the ADCAn regis-
ter) is the source. In Fly-By mode a read
transaction is initialized.
1
– Device A (pointed to by the ADCAn regis-
ter) is the destination. In Fly-By mode a
write transaction is initialized.
OT The Operation Type bit specifies the operation
mode of the DMA controller.
0
– Single-buffer mode or double-buffer mode
enabled.
1
– Auto-Initialize mode enabled.
BPC The Bus Policy Control bit specifies the bus
policy applied by the DMA controller. The op-
eration mode can be either intermittent (cycle
stealing) or continuous (burst).
0
– Intermittent operation. The DMAC chan-
nel relinquishes the bus after each trans-
action, even if the request is still asserted.
1
– Continuous operation. The DMAC chan-
nel n uses the bus continuously as long
as the request is asserted. This mode can
only be used for software DMA requests.
For hardware DMA requests, the BPC bit
must be clear.
SWRQ The Software DMA Request bit is written with
a 1 to initiate a software DMA request. Writing
a 0 to this bit deactivates the software DMA
request. The SWRQ bit must only be written
when the DMRQ signal for this channel is in-
active (DMASTAT.CHAC = 0).
0
– Software DMA request is inactive.
1 – Software DMA request is active.
ADA If the Device A Address Control bit is set, it en-
ables updating the Device A address.
0 – ADCAn address unchanged.
1 – ADCAn address incremented or decre-
mented, according to INCA field of
DMACNTLn register.
INCA The Increment/Decrement ADCAn field spec-
ifies the step size for the Device A address in-
crement/decrement.
00 – Increment ADCAn register by 1.
01 – Increment ADCAn register by 2.
10 – Decrement ADCAn register by 1.
11 – Decrement ADCAn register by 2.
ADB If the Device B Address Control bit is set, it en-
ables updating the Device B Address.
0
– ADCBn address unchanged.
1
– ADCBn address incremented or decre-
mented, according to INCB field of
DMACNTLn register.
INCB The Increment/Decrement ADCBn field spec-
ifies the step size for the Device B address in-
crement/decrement.
00 – Increment ADCBn register by 1.
01 – Increment ADCBn register by 2.
10 – Decrement ADCBn register by 1.
11 – Decrement ADCBn register by 2.
15 0
Block Length
76543210
BPC OT DIR IND TCS EOVR ETC CHEN
15 14 13 12 11 10 9 8
Res. INCB ADB INCA ADA SWRQ