AD6620
SERIAL PORT CONTROL
The data is contained in the low byte of the 16 significant bits.
This data will be placed into the external interface register
pointed to by A[2 . . 0] for a write and will be ignored for a read.
In addition to providing access to the complex output data stream
of the AD6620, the Serial Port can also be used for Dynamic
Control of the device. The dynamic registers of the AD6620
that are typically programmed while the chip is processing are
listed in the table below. In order to use the serial port control,
the chip must first be booted using the microprocessor interface.
Serial Port Writes
If the WRITE bit is high and the READ bit is low then a write
access is performed to the external interface register pointed to
by A[2 . . 0]. A write to an internal register takes place by first
writing the AMR and LAR. The data registers DR4–DR1 are
then written as needed. A final write to DR0 then moves the
data to the internal register.
Table XIII. Dynamic Registers
Bit
Address Width Name
Serial Port Reads
300
302
303
304
305
307
309
30B
8
MODE CONTROL REGISTER
NCO SYNC CONTROL REGISTER
NCO_FREQ
NCO PHASE_OFFSET
INPUT/CIC2 SCALE REGISTER
CIC5 SCALE REGISTER
If the READ bit is high, then a read to the register indicated is
performed and the data will appear in the RDATA word appended
to the serial frame. The internal data read is loaded into the
serial data word in FIFO fashion. The first byte read is loaded
into the first eight bits, the second read during the frame is
loaded into the second byte, etc. Since the serial data is shifted
MSB first, the first byte will actually be loaded into the most
significant byte of the serial data word.
32
32
16
8
5
4
OUTPUT/RCF CONTROL REGISTER
RCF ADDRESS OFFSET REGISTER
8
During a frame (the period between SDFS rising edges) up to
four reads may occur. When a read is requested through the
serial port, a data word is appended to the end of the serial string.
Even if AD is not asserted (see below for AD description) a word is
added to the end of the IQ data stream. Therefore, if the chip is
in single channel mode, the I and Q data are sent followed by a
read word. If the chip is in diversity channel mode, the IQ pairs
are followed by a read word. Thus the serial port responds with
either three or five serial words in a frame, respectively. If AD is
asserted, the read word is sent each frame regardless of a request. If
no requests are made, the appended word is all zeros.
The internal address and data structure are shared between
the microprocessor port and the serial port. When accessing
the internal RAM or registers, the serial port is given priority
over a microprocessor request. If a Mode 0 access occurs on
the microport while the serial port is accessing the internal address
space, the RDY line will go low and stay low until the serial
access has been completed. If a Mode 1 access occurs on the
microport during a serial access, the DTACK signal will not go
low until the serial access has been completed. The microport is
used for booting the AD6620 and either the microport or the
serial port can be used to dynamically change the system param-
eters. Both ports may be used in the same design provided that
the handshaking rules described above are observed.
The number of reads accomplished in a frame is limited by the
serial word length. If the serial word length is 16 bits, only two
reads can be performed during a frame. If the serial word length
is 24 bits, three reads can occur in a frame. If the serial word
length is 32 bits, then up to four reads can occur in a frame.
The RDATA word format is shown below. Rows three and four
will not be present when 16-bit words are used, and row four
will not be present when 24-bit words are used.
For each word shifted out of the serial port there is a word
shifted in. Each input word can provide one internal access. Each
access can be a read or a write. All reads and writes are per-
formed via the same 8-bit registers used by the microprocessor
port. Each bit in the SDI words has a predefined meaning and
are used to decode which of these registers are being accessed
and whether the access is a read or a write. The bits are defined
according to the table below.
Table XV. RDATA Word Definition
DA7 DA6
DB7 DB6
DC7 DC6
DA5
DB5
DC5
DA4
DB4
DC4
DA3
DB3
DC3
DA2
DB2
DC2
DA1 DA0
DB1 DB0
DC1 DC0
Table XIV. SDI Input Word Definition
READ WRITE
x
x
x
A2
D2
x
A1
D1
x
A0
D0
x
D7
x
D6
x
D5
x
D4
x
D3
x
DD7 DD6 DD5 DD4 DD3 DD3 DD1 DD0
The number of words in the serial frame depends on the operat-
ing mode of the chip (one or two I/Q pairs) and whether or not
a read access occurs. It also depends on the Append Data pin,
AD. When this signal is asserted, then the RDATA word is
appended to the Serial Frame regardless of whether or not a
read was performed in the frame. This allows time-slotted sys-
tems where multiple AD6620s or other devices share a serial
port of a DSP without hardware handshakes. When AD is
high and there has not been a read during the active frame,
the RDATA word is driven low and SDFE is held off for another
serial word length.
x
x
x
x
x
x
x
x
Only the first 16 bits of the SDI word contain significant data
regardless of the serial word length. The first two bits shifted in
are the READ and WRITE indicator signals. These bits control
the access type as described below and should not be asserted
simultaneously. If the Serial Port is not used for control then the
SDI pin should be tied low to disable register reads and writes.
The three address bits are the three least significant bits of the
upper byte in the 16-bit word. These three bits A[2:0] define
which of the seven external registers are accessed by the serial
port according to Table XI.
At all times, the serial interface must have time to shift all bits.
The section below Serial Port Guidelines should be consulted to
determine if sufficient time exists.
REV. A
–35–
ADI [ ADI ]
