AD6620
the SDO of the master AD6620 takes control of the SDO line
and begins shifting data out of the device. When all data has
been shifted, the master raises the SDFE on the last shifted.
This signals the next chip (slave) that on the next cycle of the
clock it should take control of the SDO line and begin shifting
data to the DSP. When the second AD6620 completes its shift,
it raises its SDFE to signal the next chip in the chain, if present.
If additional devices are connected to the chain, this would be
used to indicate they should take control on the next clock cycle.
This application does not have a third device and therefore, the
frame would end.
Software for Single Channel Real Operation
When interfacing Analog Device’s SHARC DSP, the following
code fragments can be used to configure the SHARC. The first
example shows how to configure the registers for use with a single
channel application. The first segment of code defines the memory
for use with the multichannel serial port data. The second segment
of code sets up the serial port for receiving data only. It could
have just as easily been set up for bidirectional data by properly
setting the MTCSI register. The final two code segments are used
when a serial port interrupt occurs. When the SHARC detects
completion of the serial port frame, an interrupt is generated
and the final code segment is executed. The comments in that
section show where user code should be inserted. The SHARC
takes care of moving the serial port buffers data directly to data
memory as shown.
Normally in an application with a single AD6620, the AD6620
would be configured as the serial bus master. However, there
are applications where the DSP or other device may be the serial
bus master. In this case, the diagram below illustrates how to
configure the AD6620 so that it may be used in this mode. In
order to use this in a meaningful application, the DSP must
know when the AD6620 has new data available on its output. If
the DSP polls the AD6620 too early, either old data will be present
or the data could be in an indeterminate state. To prevent this,
the AD6620 has an output pin DVOUT that signals the DSP
when new data is available. This should be tied to an interrupt
line of the DSP that is edge-sensitive, as the DVOUT line is only
valid for two or four high speed clock cycles depending on the
mode of the chip. The DSP may then invoke an interrupt service
routine to handle the data, see text below. In this application,
the DSP is responsible for generating the framing and clocking
signals to the AD6620 as shown in Figure 51.
/* —————————————————————————————*/
/* multi-channel register setup */
.SEGMENT/DM dm_data;
.VAR fm_demod_data[2];
/* Array for receiving 1 real and imag
sample */
.VAR fm_demod_tcb[8] = 0, 0, 0, 0, fm_demod_data+7, 2, 1,
fm_demod_data; /* Transfer Control Block for reception of fm data */
/* —————————————————————————————*/
/* —————————————————————————————*/
/* Subroutine to setup sport1 for use with the AD6620 */
2
4
setup_sport1:
WL
AD SDIV
r0 = 0;
/* multi-channel enable setup */
SCLK
SDI
SCLK
DT
dm(MTCS1) = r0;
/* do not transmit on any channels */
DSP
AD6620
SDO
SDFS
SDFE
DR
r0 = 0;
/* Compand Setup */
RFS
dm(MTCCS1) = r0; /* no companding on transmit */
dm(MRCCS1) = r0; /* no companding on receive */
SBM
r0 = 0x00100000;
dm(STCTL1) = r0;
/* Setup sport 1 transmit control register */
/* mfd = 1 */
+3.3V
2
4
r0 = 0x038c20f2;
dm(SRCTL1) = r0;
/* Setup sport 1 receive control register */
/* slen = 15, sden & schen enabled */
/* sign extend, external SCLK+RFS */
WL
AD SDIV
SCLK
SDI
AD6620
CASCADE
SDO
SDFS
SDFE
r0 = fm_demod_tcb + 7; /* TCB address */
dm(CP1) = r0;
10k⍀
10k⍀
/* Kickoff DMA chain */
SBM
rts (db);
/* RETURN */
bit set imask SPR1I; /* enable sport1 receive interrupt */
nop;
Figure 50. Dual AD6620s Using the Serial Bus in a TDM
Application
/* —————————————————————————————*/
spr1_svc:
jump spr1_asserted;
RTI;
2
4
RTI;
RTI;
WL
AD SDIV
SCLK
SCLK
DT
/* —————————————————————————————*/
/* —————————————————————————————*/
/* Process received data here. Data samples located in fm_demod_data
and fm_demod_data+1
SDI
DSP
AD6620
SDO
DR
SDFS
RFS
10k⍀
10k⍀
SDFE
DV
OUT
IRQ
SBM
spr1_asserted:
push sts;
/* Push the status stack */
Figure 51. AD6620 Configured as a Serial Slave
REV. A
/* Use secondary set of DAGs and Register file */
–39–
ADI [ ADI ]
