iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC14/36
Connecting the ABZ Outputs
Connecting the Serial Ports
The iC-TW8 provides industry-standard quadrature
incremental outputs at OUTA (pin 18) and OUTB
(pin 17). If an index sensor is connected to the
ZERO inputs of the iC-TW8, a Z output synchro-
nous with the AB outputs is also available on OUTZ
(pin 16). These outputs can be directly connected to
an encoder counter such as the iC-TW9.
The iC-TW8 contains two serial ports that may be
used to access internal registers for configuration.
These are a standard SPI (Serial Peripheral Inter-
face) slave port and a 1-wire port, both of which
utilize the same communication protocol (see Serial
Communication Ports in the Programmer’s Refer-
ence for the protocol definition). Both ports may be
used simultaneously.
Alternatively, the ABZ outputs can be connected to
a differential line driver (such as the iC-HD7 or iC-
HX) as shown in Figure 16. When using a line driv-
er it is especially important to isolate the iC-TW8
from external switching noise using a regulator, as
shown.
The SPI slave port uses a 3-wire or 4-wire full-
duplex interface which operates in CPOL = 0 and
CPHA = 0 mode only. This means that the base
(resting) value of SPI_SCLK (pin 27) is low, SPI_SI
(pin 10) is sampled on the rising edge of
SPI_SCLK, and SPI_SO (pin 9) is changed on the
falling edge of SPI_CLCK.
24V
regulator
3.3V
regulator
5V
When using a 4-wire SPI interface, the SPI_xSS
input (pin 14) is used to enable the SPI port when-
ever communication is required. When using a 3-
wire SPI interface, the SPI_xSS input must be tied
to DVSS.
line driver
AVDD
DVDD
VCC
VB1
VB2
VB3
A1
OUTA
OUTB
OUTZ
E1
E3
E5
The 1-wire port uses a single bi-directional data line
connected to IR (pin 7) for communication. The bit
stream is pulse-width modulated: a 1-bit is encoded
as a long high level followed by a short low level, a
0-bit is encoded as a short high level followed by a
long low level. A timeout circuit activates a status
bit in the STAT_SP register (see Programmer’s
Reference) in the event of an illegal transaction.
A2
A3
A4
AVSS/DVSS
GNDx
A5
A6
iC-TW8
iC-HX
Figure 16: Line Driver Connection
Power-on-Reset
The iC-TW8 contains a built-in power-on-reset
(POR) circuit that controls the safe start-up of the
device. The internal POR can be configured for
two thresholds, 2.7V for use with 3.3V supplies or
4V, which is recommended when operating the
iC-TW8 at 5V. Connect xRST (pin 2) DVDD or
leave it unconnected (xRST has an internal 40kΩ
pullup resistor to DVDD) to select a power-on-reset
threshold of 2.7V. Connect xRST to ground through a
68kΩ resistor to select a threshold of 4V. An external
reset source (such as an RC circuit) can also be con-
nected to xRST (pin 2) to directly control the POR
behavior.
Connect xRST to DVSS via 68kΩ
resistor for 4V POR threshold.
DVDD
xRST
xRST
68kΩ
Connect xRST to DVDD (or leave
floating) for 2.7V POR threshold.
iC-TW8
iC-TW8
DVSS
Figure 17: Setting the Power-On-Reset Threshold
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