AD1846 Analog Devices, AD1846 Datasheet - Page 22

• Manufacturer Part Number: AD1846
• Description: Low Cost Parallel-port 16-bit Soundport Stereo Codec
• Manufacturer: Analog Devices

AD1846
Direct Memory Access (DMA) Transfers
The second type of bus cycle supported by the AD1846 are
DMA transfers. Both dual channel and single channel DMA op-
erations are supported. To enable Playback DMA transfers,
playback enable (PEN) must be set and PPIO cleared. To en-
able Capture DMA transfers, capture enable (CEN) must be set
and CPIO cleared. During DMA transfers, the AD1846 asserts
HI the Capture Data Request (CDRQ) or the Playback Data
Request (PDRQ) followed by the host’s asserting LO the DMA
Capture Data Acknowledge (CDAK) or Playback Data Ac-
knowledge (PDAK), respectively. The host’s asserted Acknowl-
edge signals cause the AD1846 to perform DMA transfers. The
input address lines, ADR1:0, are ignored. Data is transferred
between the proper internal sample registers.
The read strobe (RD) and write strobe (WR) delimit valid data
for DMA transfers. Chip select (CS) is a “don’t care”; its state
is ignored by the AD1846.
The AD1846 asserts the Data Request signals, CDRQ and
PDRQ, at the rate of once per sample period. PDRQ is asserted
near the beginning of an internal sample period and CDRQ is
asserted late in the same period to maximize the available pro-
cessing time. Once asserted, these signals will remain active HI
until the corresponding DMA cycle occurs with the host’s Data
Acknowledge signals. The Data Request signals will be
deasserted after the falling edge of the final RD or WD strobe in
the transfer of a sample, which typically consists of multiple
bytes. See “Data Ordering” above for a definition of “sample.”
WR INPUT
OUTPUTS
CS INPUT
OUTPUT
OUTPUT
DATA7:0
ADR1:0
INPUTS
INPUTS
CDRQ/
DBDIR
INPUT
PDRQ
PDAK
DBEN
Figure 12. Control Register/PIO Write Cycle
HI
t
SUDK1
t
ADSU
t
CSSU
t
t
WDSU
DBDL
t
STW
t
CSHD
t
SUDK2
t
t
DHD2
ADHD
–22–
DMA transfers may he independently aborted by resetting the
Capture Enable (CEN) and/or Playback Enable (PEN) bits in
the Interface Configuration Register. The current capture
sample transfer will be completed if a capture DMA is termi-
nated. The current playback sample transfer must be completed
if a playback DMA is terminated. If CDRQ and/or PDRQ are
asserted HI while the host is resetting CEN and/or PEN, the re-
quest must be acknowledged. The host must assert CDAK and/
or PDAK LO and complete a final sample transfer.
Single-Channel DMA
Single-Channel DMA mode allows the AD1846 to be used in
systems with only a single DMA channel. It is enabled by setting
the SDC bit in the Interface Configuration Register. All cap-
tures and playbacks take place on the playback channel. Obvi-
ously, the AD1846 cannot perform a simultaneous capture and
playback in Single-Channel DMA mode.
Playback will occur in single-channel DMA mode exactly as it
does in Two-Channel mode. Capture, however, is diverted to
the playback channel which means that the capture data request
occurs on the PDRQ pin and the capture data acknowledge
must be received on the PDAK pin. The CDRQ pin will remain
inactive LO. Any inputs to CDAK will be ignored.
Playback and capture are distinguished in Single-Channel DMA
mode by the state of the playback enable (PEN) or capture
enable (CEN) control bits. If both PEN and CEN are set in
Single-Channel DMA mode, playback will be presumed.
To avoid confusion of the origin of a request when switching be-
tween playback and capture in Single-Channel DMA mode,
both CEN and PEN should be disabled and all pending re-
quests serviced before enabling the alternative enable bit.
Switching between playback and capture in Single-Channel
DMA mode does not require changing the PPIO and CPIO bits
or passing through the Mode Change Enable state except for
initial setup. For setup, assign zeros to both PPIO and CPIO.
This configures both playback and capture for DMA. Then,
switching between playback and capture can be effected entirely
by setting and clearing the PEN and CEN control bits, a tech-
nique which avoids having to enter the Mode Change Enable
state.
REV. A