7.5 Programming
The DACx300x are programmed through either a 3-wire SPI or 2-wire I
2
C interface. A 4-wire SPI mode is
enabled by mapping the GPIO pin as SDO. The SPI readback operates at a lower SCLK than the standard
SPI write operation. The type of interface is determined based on the first protocol to communicate after device
power up. After the interface type is determined, the device ignores any change in the type while the device is
on. The interface type can be changed after a power cycle.
7.5.1 SPI Programming Mode
An SPI access cycle for DACx300x is initiated by asserting the SYNC pin low. The serial clock, SCLK, can be
a continuous or gated clock. SDI data are clocked on SCLK falling edges. The SPI frame for DACx300x is 24
bits long. Therefore, the SYNC pin must stay low for at least 24 SCLK falling edges. The access cycle ends
when the SYNC pin is deasserted high. If the access cycle contains less than the minimum clock edges, the
communication is ignored. By default, the SDO pin is not enabled (three-wire SPI). In the three-wire SPI mode,
if the access cycle contains more than the minimum clock edges, only the first 24 bits are used by the device.
When SYNC is high, the SCLK and SDI signals are blocked, and SDO becomes Hi-Z to allow data readback
from other devices connected on the bus.
describe the format for the 24-bit SPI access cycle. The first byte input to SDI is the
instruction cycle. The instruction cycle identifies the request as a read or write command and the 7-bit address
that is to be accessed. The last 16 bits in the cycle form the data cycle.
Table 7-12. SPI Read/Write Access Cycle
BIT
FIELD
DESCRIPTION
23
R/W
Identifies the communication as a read or write command to the address register: R/W = 0 sets a write
operation. R/W = 1 sets a read operation
22-16
A[6:0]
Register address: specifies the register to be accessed during the read or write operation
15-0
DI[15:0]
Data cycle bits: If a write command, the data cycle bits are the values to be written to the register with
address A[6:0]. If a read command, the data cycle bits are
don't care
values.
1
24
8
9
D23
D16
D15
D0
Write command
SYNC
SCLK
SDI
SDO
1
24
8
9
D23
D16
D15
D0
Any command
D23
D16
D15
D0
HiZ
HiZ
HiZ
Write command echo
Figure 7-14. SPI Write Cycle
Read operations require that the SDO pin is first enabled by setting the SDO-EN bit in the INTERFACE-CONFIG
register. This configuration is called four-wire SPI. A read operation is initiated by issuing a read command
access cycle. After the read command, a second access cycle must be issued to get the requested data.
and
show the output data format. Data are clocked out on the SDO pin either on the falling
edge or rising edge of SCLK according to the FSDO bit (see also
Table 7-13. SDO Output Access Cycle
BIT
FIELD
DESCRIPTION
23
R/W
Echo R/W from previous access cycle
22-16
A[6:0]
Echo register address from previous access cycle
15-0
DI[15:0]
Readback data requested on previous access cycle
DAC53001, DAC53002, DAC63001, DAC63002
SLASF48 – MAY 2022
46
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