Signal Processing; Digital Communications State Machine; 2-Wire Current Modulated Interface; Synchronous Operation And Dual Device Bus - Analog Devices ADXL180 iMEMS Manual

SIGNAL PROCESSING

The ADXL180 contains an on-board set of signal processing
blocks both prior to and after ADC conversion. The first stage is
a fully differential, switched capacitor, low-pass, three-pole
Bessel filter. Range scaling is also handled in one of the filter
blocks, enabling 50 g to 500 g range capability. At this point, an
analog output test signal (V
SCO
diagnostic mode. The signal then converts by a 10-bit rail-to-rail
SAR ADC. In the digital section, an auto-zero routine is
available to the user as part of the state machine in addition to
error detection features such as offset drift detection.

DIGITAL COMMUNICATIONS STATE MACHINE

The ADXL180 digital state machine is based on a Core 5 phase
state machine implemented in high density CMOS. This state
machine handles the sequential states of
Phase 1. Initialization.
Phase 2. Device data transmission, including individual serial
number and user-programmed data.
Phase 3. Self-diagnostic, including automatic full electro-
mechanical self-test with internal error detection
available.
Phase 4. Auto-zero initialization, if selected. During this phase,
acceleration data is already available.
Phase 5. Normal acceleration data transmission.

2-WIRE CURRENT MODULATED INTERFACE

The data that is generated during these five phases is trans-
mitted using a 2-wire high voltage communication port. This
allows the device to be powered by a fixed supply voltage, and
communicate back to the system or ECU electronics by modulating
current. Current modulated messages are encoded using Man-
chester encoding.
Table 5. Factory Programmed and User-Programmed Memory
Configuration Mode
Programmed By Register Address
User 0000b
0001b
0010b
0011b
Factory 1011b
1100b
1101b
1110b
1111b
) is available to the user in a
Configuration Mode
Register Name
UREG
CREG0
CREG1
CREG2
SN0
SN1
SN2
SN3
MFGID
SYNCHRONOUS OPERATION AND DUAL DEVICE
BUS
In a point-to-point bus topology, the ADXL180 supports asyn-
chronous transmission of data to the receive device every 228 μs,
controlled by the on-board state machine. A synchronous option
is also available, allowing two devices to be on the same bus
using time division multiplexing where each device transmits its
data during a known time slot.
Synchronization is achieved by voltage modulated synchronization
pulses, configuring the ADXL180 device into a synchronous
mode, and establishing data frame time slots. The high voltage
communication port registers valid synchronization pulses and
enables message-by-message advancement of the state machine
rather than asynchronous timed regular data transmission.

PROGRAMMED MEMORY AND CONFIGURABILITY

Factory-Programmed Serial Number and Manufacturer
Information
The ADXL180 includes a 32-bit factory-programmed serial
number, as shown in Table 5. This serial number transmits
during Phase 2 of startup for all devices to enable robust quality
tracking of individual devices, and it is field readable. In addition,
this data includes revision information and manufacturer identi-
fication in case multiple devices used within a single application
are from different manufacturers or generations of parts.
User-Programmable Data Register
The ADXL180 gives the user an 8-bit register of user-program-
mable data, which is transmitted during Phase 2 of the state
machine. In addition, the UD8 bit, a ninth user-available bit,
is transmitted separately during Phase 2 and can be used for
various purposes, such as orientation definition or module type.
MSB
D7 D6 D5
UD7 UD6 UD5
UD8 BDE MD1
STI AZE SYEN
CUPRG CUPAR SCOE
SNB7 SNB6 SNB5
SNB15 SNB14 SNB13 SNB12 SNB11 SNB10
SNB23 SNB22 SNB21 SNB20 SNB19 SNB18
SNB31 SNB30 SNB29 SNB28 SNB27 SNB26
SNPRG SNPAR REV2
Rev. 0 | Page 11 of 56
D4 D3 D2 D1
UD4 UD3 UD2 UD1
MD0 FDLY DLY2 DLY1
ADME ERC SVD DAT
FC1 FC0 RG2 RG1
SNB4 SNB3 SNB2 SNB1
SNB9
SNB17
SNB25
REV1 REV0 MFGID2 MFGID1 MFGID0
ADXL180
LSB
D0
UD0
DLY0
MAN
RG0
SNB0
SNB8
SNB16
SNB24