iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC15/36
Startup
Serial Configuration Overview
In operation, the startup sequence is initiated when
power is applied to the iC-TW8. However, a startup
sequence can also be initiated by external hardware
connected to the xRST input (pin 2), or by the Re-
start command (write 0x40 to 0x80B0). See the iC-
TW8 Programmer’s Reference for more information
on executing commands.
In serial configuration mode, values for all configu-
ration variables must be written to the TW8’s inter-
nal CFG block registers before the device can be
used. The easiest way to accomplish this is to use
the free encoder design tools along with the iC-TW8
demo board and the free Graphical User Interface
(GUI) software. The encoder design tools—in the
form of Excel spreadsheets—allow entering applica-
tion parameters in engineering units and then pro-
vide configuration register values that can be direct-
ly written to the iC-TW8 using the GUI software.
The encoder design tools also provide performance
limits and graphs and configuration documentation.
After power-up, the iC-TW8’s POR circuit monitors
the supply voltage and waits until it has reached the
appropriate threshold (as determined by the xRST
connections). The iC-TW8 then starts up using the
internal oscillator (even if a crystal or external clock
source is connected) and executes its start-up cycle
as outlined here.
The iC-TW8 TW8_1D evaluation board implements
the iC-TW8 along with a 24AA02 EEPROM,
24MHz crystal, and an SPI interface (with 3.3V to
5V level shifter if required) to the iC-MB3U-I2C PC
adapter for direct communication with the GUI
software. A functional prototype can thus be quickly
assembled by connecting only a sensor and optional
line driver. See the TW8_1D evaluation board doc-
umentation for more information.
1. Read configuration and parameter values
from EEPROM.
2. Set proper clock source and frequency.
3. Enable the signal path.
4. Wait for all analog circuitry to settle.
5. Clear all errors.
Once the iC-TW8 has been configured, the AB sig-
nal path must be calibrated to determine proper val-
ues for gain, offset correction, gain match correc-
tion, and phase correction. This is most easily done
using the Auto Calibration feature of the iC-TW8 to
automatically determine optimum parameter values.
Alternatively, initial parameter values may be writ-
ten over the serial interface and allowed to adapt.
The adapted parameter values can then be written to
the EEPROM.
6. Start ABZ output generation.
If any errors are detected during the start-up cycle,
the iC-TW8 does not enable the outputs but goes
into an idle state with ERR (pin 20) asserted (low).
The amount of time the iC-TW8 waits for the ana-
log circuitry to settle (twait) is configured using the
internal variable MAIN_OUT.start.
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