PNI RM3100 Evaluation Board - Manual (Page 18)

PNI Sensor Corporation Doc 1017252 r02
RM3100 Evaluation Board User Manual Page 17 of 33
5.1 Set the Cycle Count Registers (0x04
– 0x09)
The Cycle Count Registers establish the number of sensor oscillation cycles (cycle counts)
that will be counted for each sensor in both the forward and reverse bias directions during a
measurement sequence. Each sensor has its own cycle count value, and each can be
different. Increasing the cycle count value increases measurement gain and resolution.
Lowering the cycle count value reduces acquisition time, which increases maximum
achievable sample rate or, with a fixed sample rate, decreases power consumption. The
Cycle Count read and write addresses, plus their default values, are given in Table 5-2
Table 5-2: Cycle Count Registers
Register Description
Default
Value (Hex)
Write Address
(Hex)
Read Address
(Hex)
X Axis Cycle Count Value - MSB 0x00 04 84
X Axis Cycle Count Value - LSB 0xC8 05 85
Y Axis Cycle Count Value - MSB 0x00 06 86
Y Axis Cycle Count Value - LSB 0xC8 07 87
Z Axis Cycle Count Value - MSB 0x00 08 88
Z Axis Cycle Count Value - LSB 0xC8 09 89
Since the registers are adjacent, it is not necessary to send multiple register addresses, as the
RM3100 Evaluation Board automatically will read/write to the next adjacent register.
The default values for the Cycle Count Registers are 0xC8 in the LSB and 0x0 in the MSB,
or 200
D
. This default value provides a good trade-off between acquisition time and
resolution, but favors resolution. If the user is more interested in low power consumption or
running at high data rates, a lower cycle count value of (ex. 50
D
or 100
D
) would be more
appropriate. To estimate the appropriate cycle count value for your application review the
specifications given at 50, 100, and 200 cycle counts in Table 3-1. Note that these 3 cycle
counts by no means represent all the cycle count options, as the minimum value is ‘0’ and the
maximum is 65,536. Having said this, quantization issues generally dictate working above a
cycle count value of ~30, while noise limits the useful upper range to ~400 cycle counts.
Assuming a non-default cycle count value is desired, then prior to sending a command to
take a sensor measurement it is necessary to Write values to the Cycle Count Registers.
Once the Cycle Count Registers are set, they do not need to be repopulated unless the user
wants to change the values or the system is powered down, in which case the default value
repopulates the register fields when powered up again.