READING THE MEMORY MAP REGISTER TABLE
Each row in the memory map register table has eight bit locations.
The memory map is roughly divided into three sections: the chip
configuration registers (Address 0x00 to Address 0x02); the
channel index and transfer registers (Address 0x05 and
Address 0xFF) and the ADC functions registers, including setup,
control, and test (Address 0x08 to Address 0x102).
The memory map register table (see Table 18) lists the default
hexadecimal value for each hexadecimal address shown. The
column with the heading Bit 7 (MSB) is the start of the default
hexadecimal value given. For example, Address 0x05, the device
index register, has a hexadecimal default value of 0x03. This
means that in Address 0x05 Bits[7:2] = 0, and Bits[1:0] = 1. This
setting is a default channel index setting. The default value
results in both ADC channels receiving the next write
command. For more information on this function and others, see
the AN-877 Application Note, Interfacing to High Speed ADCs via
SPI. This application note details the functions controlled by
Register 0x00 to Register 0xFF. The remaining registers, are
documented in the Memory Map Register Description section.
All address and bit locations that are not included in Table 18
are not currently supported for this device. Unused bits of a
valid address location should be written with 0s. Writing to these
locations is required only when part of an address location is
open (for example, Address 0x05). If the entire address location
is open (for example, Address 0x13), this address location should
not be written to.
After the AD9648 is reset, critical registers are loaded with
default values. The default values for the registers are given in
the memory map register table, Table 18.
An explanation of logic level terminology follows:
• “Bit is set” is synonymous with “bit is set to Logic 1” or
“writing Logic 1 for the bit.”
• “Clear a bit” is synonymous with “bit is set to Logic 0” or
“writing Logic 0 for the bit.”
Some channel setup functions, such as the signal monitor
thresholds, can be programmed differently for each channel. In
these cases, channel address locations are internally duplicated for
each channel. These registers and bits are designated in Table 18
as local. These local registers and bits can be accessed by setting
the appropriate Channel A or Channel B bits in Register 0x05.
If both bits are set, the subsequent write affects the registers of
both channels. In a read cycle, only Channel A or Channel B
should be set to read one of the two registers. If both bits are set
during an SPI read cycle, the part returns the value for Channel A.
Registers and bits designated as global in Table 18 affect the entire
part or the channel features for which independent settings are not
allowed between channels.
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