National CP3BT26 - Manual (Page 46)

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CP3BT26
9.6.8 DMA Status Register (DMASTAT)
The DMA status register is a byte-wide, read register that
holds the status information for the DMA channel n. This
register is cleared at reset. The reserved bits always return
zero when read. The VLD, OVR and TC bits are sticky (once
set by the occurrence of the specific condition, they remain
set until explicitly cleared by software). These bits can be in-
dividually cleared by writing 1 to the bit positions in the DM-
ASTAT register to be cleared. Writing 0 to these bits has no
effect
TC The Terminal Count bit indicates whether the
transfer was completed by a terminal count
condition (BLTCn Register reached 0).
0
– Terminal count condition did not occur.
1 – Terminal count condition occurred.
OVR The behavior of the Channel Overrun bit de-
pends on the operation mode (single buffer,
double buffer, or auto-initialize) of the DMA
channel.
In double-buffered mode (DMACNTLn.OT =
0):
The OVR bit is set when the present transfer
is completed (BLTCn = 0), but the parameters
for the next transfer (address and block
length) are not valid (DMASTAT.VLD = 0).
In auto-initialize mode (DMACNTLn.OT = 1):
The OVR bit is set when the present transfer
is completed (BLTCn = 0), and the DMAS-
TAT.TC bit is still set.
In single-buffer mode:
Operates in the same way as double-buffer
mode. In single-buffered mode, the DMAS-
TAT.VLD bit should always be clear, so it will
also be set when the DMASTAT.TC bit is set.
Therefore, the OVR bit can be ignored in this
mode.
CHAC The Channel Active bit continuously indicates
the active or inactive status of the channel,
and therefore, it is read only. Data written to
the CHAC bit is ignored.
0
– Channel inactive.
1 – Indicates that the channel is active
(CHEN bit in the CNTLn register is 1 and
BLTCn > 0)
VLD The Transfer Parameters Valid bit specifies
whether the transfer parameters for the next
block to be transferred are valid. Writing the
BLTRn register automatically sets this bit. The
bit is cleared in the following cases:
„ The present transfer is completed and the
ADRAn, ADRBn (indirect mode only), and
BLTR registers are copied to the ADCAn,
ADCBn (indirect mode only), and BLTCn
registers.
„ Writing 1 to the VLD bit.
7 4 3 2 1 0
Reserved VLD CHAC OVR TC