SoundTraxx DSD-150/DSX Technical Reference - Manual (Page 11)

Address Mode Direct Mode
Register Mode Ops Mode Short Form
Paged Mode Ops Mode Long Form
Digital Sound Decoder Technical Reference 11
❐ ■
❐ ❐
■ ■
CV 9
PWM PERIOD
Description
Determines the PWM period of the motor drive signals:
bit 7 bit 0
D7 D6 D5 D4 D3 D2 D1 D0
D0-D7: PWM Period
The motor PWM period in microseconds is computed as:
Period = (255 - CV9) * 204.8
This CV may be programmed with any value between 0 and 230 corresponding to a PWM period
range of 52.2µS to 5.12µS. The motor drive frequency can be found by taking the reciprocal of
the period. The drive frequency can thus be programmed from 19.1 Hz to 195 Hz.
The decoder will ignore commands that attempt to program this register with values greater than
230.
The correct value for this register will vary depending upon the locomotive the DSD is installed in
and it may take some experimentation to find the optimal value. Generally, the selected value will
require a trade-off decision between motor torque and audible noise. Lower numbers will pro-
duce more torque but may cause the motor and driveline to resonate and buzz loudly. On smaller
engines that lack traction, sufficient torque can be produced to cause the drive wheels to slip.
Higher numbers, on the other hand, will tend to reduce the buzzing noise but there may be some
loss in power, especially at low speeds. The following values are provided as a guide line to help
establish a starting point for determining the best PWM period value:
Scale CV9 Value
N, HOn3 180-200
HO, S 175-185
O 160-175
G 120-160
Note: CV 9 also affects the modulation period of the Hyperlight effects. When using the Hyperlight ef-
fects, it is recommended that CV 9 be programmed with values greater than 155 as an annoying flicker
may otherwise result.
Default Value: 180 (0xB4), Corresponds to 65Hz drive frequency.