AMC7820 Datasheet, PDF (22/28 Pages) Texas Instruments – ANALOG MONITORING AND CONTROL

DIGITAL INTERFACE
The AMC7820 communicates through a standard SPI bus,
which consists of four wires: SCLK (the serial clock pin),
MISO (Master-Out Slave-In data pin), MOSI (Master-In Slave-
Out data pin), and SS (Slave Select pin). The SPI master
device activates the slave select signal (SS = LOW) to
access the selected SPI slave device and generates SCLK
to synchronize the movement of the data both in and out of
the slave devices through the MOSI and MISO pins. The SPI
slave devices depend on a master to start and synchronize
transmissions.
A transmission begins when initiated by an SPI master. The
word from the master is shifted into the AMC7820 through
the MOSI pin under the control of the master serial clock,
SCLK. The word from the AMC7820 registers (the slave) is
shifted out from the MISO pin under control of SCLK as well.
The idle state of the serial clock for the AMC7820 is LOW,
which corresponds to a clock polarity setting of 0 (typical
microprocessor SPI control bit CPOL = 0). The AMC7820
interface is designed with a clock phase setting of 1 (typical
microprocessor SPI control bit CPHA = 1). In both the master
and slave, the data is shifted out on the rising edge of SCLK
and sampled on the falling edge of SCLK, where the data is
stable. The master begins driving its MOSI pin on the first
rising edge of SCLK after SS is activated (SS = LOW).
To write data into the AMC7820, the host activates the slave
select signal (SS = LOW) and issues a WRITE command to
start the data transmission. The AMC7820 always interprets
the first word (from the host) immediately following the falling
edge of the SS signal as a command. The data to be written
into the AMC7820 follows the command. SS must remain
LOW until all data is transmitted (see Figure 13), otherwise
the WRITE operation is terminated. Likewise, to read the
data from the AMC7820, the host activates the slave select
signal and sends a READ command. Then the AMC7820
sends data out through the MISO pin under control of SCLK.
SS must remain LOW until all data is shifted out (see Figure
13), otherwise the transmission is terminated.
When the operation is terminated, the master must issue a
new command to start a new operation. In the AMC7820, all
data is 16-bit. It takes 16 clock cycles of SCLK to transfer one
word of data.
AMC7820 COMMUNICATION PROTOCOL
The AMC7820 is entirely controlled by registers. Reading
and writing these registers is accomplished by a 16-bit
command that is sent prior to the data for that register. The
command is constructed, as shown in Table I.
The command word begins with a R/W bit that specifies the
direction of data flow. The following 4 bits specify the page
of memory this command is directed to, as shown in Table
II. The next five bits specify the register address on that
page of memory to which the data is directed. The last six
bits are reserved for future use.
PG3
PG2
PG1
PG0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
TABLE II. Page Addressing.
PAGE ADDRESSED
0
1
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
To read all the first page of memory, for example, the host
processor must send the command 0x8000—this specifies
a read operation beginning at Page 0, Address 0. The
processor can then start clocking data out of the AMC7820.
The AMC7820 will automatically increment its address
pointer to the end of the page; if the host processor
continues clocking data out past the end of a page, the
address will wrap around to the beginning of the page. This
is true of either reading or writing, so it is important that the
host makes sure of the address to which it is writing.
Likewise, writing to Page 1 of memory would consist of the
processor writing the command 0x0800 (which would specify
a write operation) with PG0 set to 1, and all the ADDR bits
set to 0. This would result in the address pointer pointing at
the first location in memory on Page 1 of memory. See the
AMC7820 Memory Map section for details of register loca-
tions. To make correct R/W operations, the host must issue
SS and SCLK properly.
Bit 15
MSB
R/W
Bit 14
PG3
Bit 13 Bit 12
PG2 PG1
Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5
PG0 ADDR4 ADDR3 ADDR2 ADDR1 ADDR0 X
NOTE: R/W = 1 when reading; 0 when writing. X = Don’t care.
TABLE I. AMC7820 Command Word.
Bit 4
X
Bit 3
X
Bit 2 Bit 1
X
X
Bit 0
LSB
X
22
AMC7820
www.ti.com
SBAS231B