ISLA112P25MREP Datasheet, PDF (21/29 Pages) Intersil Corporation – Low Power 12-Bit, 250MSPS ADC

ISLA112P25MREP
read from at a given time (again, only in three-wire
mode). If multiple slave devices are selected for reading
at the same time, the results will be indeterminate.
The communication protocol begins with an
instruction/address phase. The first rising SCLK edge
following a high to low transition on CSB determines the
beginning of the two-byte instruction/address command;
SCLK must be static low before the CSB transition. Data
can be presented in MSB-first order or LSB-first order.
The default is MSB-first, but this can be changed by
setting 0x00[6] high. Figures 33 and 34 show the
appropriate bit ordering for the MSB-first and LSB-first
modes, respectively. In MSB-first mode the address is
incremented for multi-byte transfers, while in LSB-first
mode it’s decremented.
In the default mode the MSB is R/W, which determines if
the data is to be read (active high) or written. The next
two bits, W1 and W0, determine the number of data
bytes to be read or written (see Table 6). The lower 13
bits contain the first address for the data transfer. This
relationship is illustrated in Figure 35, and timing values
are given in “Switching Specifications” on page 9.
After the instruction/address bytes have been read, the
appropriate number of data bytes are written to or read
from the ADC (based on the R/W bit status). The data
transfer will continue as long as CSB remains low and
SCLK is active. Stalling of the CSB pin is allowed at any
byte boundary (instruction/address or data) if the
number of bytes being transferred is three or less. For
transfers of four bytes or more, CSB is allowed stall in
the middle of the instruction/address bytes or before the
first data byte. If CSB transitions to a high state after
that point the state machine will reset and terminate the
data transfer.
TABLE 6. BYTE TRANSFER SELECTION
[W1:W0]
BYTES TRANSFERRED
00
1
01
2
10
3
11
4 or more
Figures 37 and 38 illustrate the timing relationships for
2-byte and N-byte transfers, respectively. The operation
for a 3-byte transfer can be inferred from these
diagrams.
SPI Configuration
ADDRESS 0X00: CHIP_PORT_CONFIG
Bit ordering and SPI reset are controlled by this register.
Bit order can be selected as MSB to LSB (MSB first) or
LSB to MSB (LSB first) to accommodate various
microcontrollers.
Bit 7 SDO Active
Bit 6 LSB First
Setting this bit high configures the SPI to interpret serial data
as arriving in LSB to MSB order.
Bit 5 Soft Reset
Setting this bit high resets all SPI registers to default values.
Bit 4 Reserved
This bit should always be set high.
Bits 3:0 These bits should always mirror bits 4:7 to
avoid ambiguity in bit ordering.
ADDRESS 0X02: BURST_END
If a series of sequential registers are to be set, burst
mode can improve throughput by eliminating redundant
addressing. In 3-wire SPI mode the burst is ended by
pulling the CSB pin high. If the device is operated in
2-wire mode the CSB pin is not available. In that case,
setting the burst_end address determines the end of the
transfer. During a write operation, the user must be
cautious to transmit the correct number of bytes based
on the starting and ending addresses.
Bits 7:0 Burst End Address
This register value determines the ending address of the
burst data.
Device Information
ADDRESS 0X08: CHIP_ID
ADDRESS 0X09: CHIP_VERSION
The generic die identifier and a revision number,
respectively, can be read from these two registers.
Indexed Device Configuration/Control
ADDRESS 0X10: DEVICE_INDEX_A
A common SPI map, which can accommodate
single-channel or multi-channel devices, is used for all
Intersil ADC products. Certain configuration commands
(identified as Indexed in the SPI map) can be executed
on a per-converter basis. This register determines which
converter is being addressed for an Indexed command. It
is important to note that only a single converter can be
addressed at a time.
This register defaults to 00h, indicating that no ADC is
addressed. Therefore Bit 0 must be set high in order to
execute any Indexed commands. Error code ‘AD’ is
returned if any indexed register is read from without
properly setting device_index_A.
ADDRESS 0X20: OFFSET_COARSE AND
ADDRESS 0X21: OFFSET_FINE
The input offset of the ADC core can be adjusted in fine
and coarse steps. Both adjustments are made via an
8-bit word as detailed in Table 7.
The default value of each register will be the result of the
self-calibration after initial power-up. If a register is to be
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FN7646.0
June 25, 2010