12
Data Device Corporation
www.ddc-web.com
RD-19240
Pre 1-1-04/05-0
ponents to settle to the pre-charged level. This time will
depend on the time constant of the bandwidth components
being charged. If switching is limited to two adjacent resolu-
tions (i.e., 12 and 14) then the pre-charge amplifier can be set
up to continuously maintain the appropriate velocity voltage
on the deselected components, resulting in the fastest possi-
ble switching times. See FIGURE 13 for an example of the
input wiring connections necessary for switching-on-the-fly
between 10 and 12 bit resolution.
DUAL BANDWIDTHS
With the second set of BW component pads, the user can set
two bandwidths for the RD-19240 and choose between them. To
use two bandwidths, proceed as follows:
1) Tie UP/DN to pad -5V.
2) Choose the two bandwidths following the guidelines in the
General Setup Considerations; the RV resistor must be the
same value for both bandwidths.
3) Use the SHIFT pad to choose between bandwidths. A logic 1
selects the VEL1 components and a logic 0 selects the VEL2
components.
INTERNAL ENCODER EMULATION
The RD-19240 can be programmed to encoder emulation mode
by toggling the A_QUAD_B input to a logic 0. The U/B output pad
becomes B (LSB XOR LSB + 1). The A (LSB + 1) and B output
signals can be used in control systems that are designed to inter-
face with incremental optical encoders. To enable the Zero Index
pulse, ZIP_EN should be tied to a logic 0.
An example circuit to create a low going edge of A_QUAD_B is
depicted in FIGURE 18. If the power supply takes longer than
50ms to start up then the time constant of 50ms set in FIGURE
FIGURE 14. BENEFIT OF SWITCHING
RESOLUTION ON THE FLY
Without Switch Resolution on the Fly Implemented
With Switch Resolution on the Fly Implemented
GND
UP/DN
SHIFT
RD-19240
D1
D0
CONTROL
FIGURE 13. INPUT WIRING - SWITCHING-ON-THE-
FLY BETWEEN 12- AND 14-BIT RESOLUTION
VEL
0V
-5V
ERROR 0
D0
0V
5V
BIT
0V
5V
ERROR = 13.6 LSBs per box
Note: Depending on bandwidth, step error may be greater.
VEL
0V
-5V
ERROR 0
D0
0V
5V
BIT
0V
5V
ERROR = 1500 LSBs per box
18 will require being extended. Alternatively a system logic reset
signal or internally generated logic ‘load’ pulse can be generated
to latch in the encoder resolution.
The resolution of the incremental outputs is latched from the D0
and D1 inputs on the low going edge of A_QUAD_B. The resolu-
tion of the parallel data outputs may be changed any time after
the encoder resolution is latched (see FIGURE 17).
Note: Depending on bandwidth, step error may be greater.
Also, less velocity / movement will lessen the error
glitch shown in the graph. The graph shows a worst
case condition based upon one bandwidth and track-
ing rate set-up. Worst case is when the overshoot on
the velocity hits the saturation point as per the graph.