AD6620
Read Pseudocode
int read_micro(ext_address);
Auto Increment Feature
To increase throughput, an auto increment feature is provided.
This feature is controlled by Bits 6 and 7 of the AMR. If these
bits are set to 00, the address remains the same after an internal
access. If set to 01, the address is incremented after a read access
has been performed. If set to 10, the address is incremented
after a write access is performed. If set to 11, the address is incre-
mented after each access, read or write. This allows the AD6620
to be initialized in a much shorter time since the access to the
LAR and AMR must occur only once to initialize or read-back
the entire device.
main();
{
/* This code shows the reading of the NCO frequency register
using the read_micro function as defined above. The variable
address is the External Address A[2..0] and data is the value to
be placed in the external interface register. The NCO register is
located at Internal Address = 0x303.
*/
// holding registers for NCO byte wide access data
int d3, d2, d1, d0;
MICROPORT CONTROL
// NCO frequency word (32-bits wide)
External reads and writes are accomplished in one of two modes
via the Microprocessor Port. The CS, RD (DS), RDY (DTACK),
WR (R/W) and MODE pins are used to control the access. The
specific function of these pins depends on whether the access is
MODE 0 or MODE 1. The Mode 1 signal names are those
listed on the pinout. The access mode is controlled by the
MODE input as described in the following sections.
// write AMR
write_micro(7, 0x03 );
// write LAR
write_micro(6, 0x03);
/* read D[7:0] from DR0, All data is moved from the Internal
Registers to the interface registers on this access. Reading
should be initiated with a read from DR0. Therefore, DR1,
DR2 and DR3 can be read after DR0 */
Table XII. Microprocessor Control Signals
MODE 0
MODE 1
d0 = read_micro(0) & 0xFF;
A[2:0] (Address Lines)
D[7:0] (Data Lines)
CS (Chip Select)
A[2:0] (Address Lines)
D[7:0] (Data Lines)
CS (Chip Select)
// read D[15:8] from DR1
d1 = read_micro(1) & 0xFF;
RD (Read Strobe)
DS (Data Strobe)
// read D[23:16] from DR2
d2 = read_micro(2) & 0xFF;
WR (Write Strobe)
RDY (Ready Signal)
MODE (Mode Select)
R/W (Read/Write Select)
DTACK (Data Acknowledge)
MODE (Mode Select)
// read D[31:24] from DR3
d3 = read_micro(3) & 0xFF;
The Microport is synchronous with the master clock (CLK) of
the AD6620, but the interface is not required to be. If the speed
of the interface is significantly slower than CLK, synchronicity
should not be an issue. If the interface is relatively fast com-
pared to CLK, the user may need to synchronize the Microport
to CLK or add wait states to the controlling processor. The
timing diagrams show the relationship of the control signals to
clock and the user should use these as a guide to implement a
Microport interface.
// DR4 is not needed because NCO_FREQ is only 32-bits
// Assemble 32-bit NCO_FREQ word from the 4 byte
components
NCO_FREQ = d0 + (d1 << 8) + (d2 << 16) + (d3 << 24);
} // end of main
REV. A
–32–
ADI [ ADI ]
