Datasheet

AD9257 Data Sheet
Rev. A | Page 30 of 40
MEMORY MAP
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 device index and transfer registers
(Address 0x05 and Address 0xFF); and the global ADC
functions registers, including setup, control, and test
(Address 0x08 to Address 0x109).
The memory map register table (see Table 17) 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 0x3F. This
means that in Address 0x05, Bits[7:6] = 0, and the remaining
Bits[5:0] = 1. This setting is the 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 Descriptions section.
Open Locations
All address and bit locations that are not included in Table 17
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 or not listed in Table 17 (for example, Address 0x13) this
address location should not be written.
Default Values
After the AD9257 is reset, critical registers are loaded with
default values. The default values for the registers are given in
Table 17, the memory map register table.
Logic Levels
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.”
Channel-Specific Registers
Some channel setup functions 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 17 as local. These local registers and bits
can be accessed by setting the appropriate data channel bits (A
through H) and the clock channel DCO/FCO bits (Bits[5:4]) in
Registers 0x04 and 0x05. If all the bits are set, the subsequent
write affects the registers of all channels and the DCO/FCO
clock channels. In a read cycle, only one of the channels should
be set to read one of the four local registers. If all the bits are set
during a SPI read cycle, the part returns the value for Channel
A. Registers and bits designated as global in Table 17 affect the
entire part or the channel features for which independent
settings are not allowed between channels. The settings in
Register 0x04 and Register 0x05 do not affect the global
registers and bits.