27906 Parallax Inc, 27906 Datasheet - Page 4

• Manufacturer Part Number: 27906
• Description: BASIC STAMP ACT BOARD NO PWR
• Manufacturer: Parallax Inc

Specifications of 27906

• Module/board Type: Activity Board
• For Use With/related Products: BASIC Stamp®
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

(SSRR command) along the way. Each variable has a default value when powered on, but can be directly
modified with specific commands (see the Command Set Details section for more information). A typical
speed profile for traveling a certain distance is shown in Figure 3 below.
Point
When the wheel advances toward the end point, it is really the set point that is being incrementally
advanced. Higher speeds are achieved by advancing the set point by a greater distance each increment
than for lower speeds. Since the Position Controller constantly drives the wheel to match its set point, it
is able to achieve the true overall user-set speed.
The Position Controller accelerates at the user-set speed ramp rate until it reaches the user-set speed.
Then it uses the current average speed to calculate the distance required to decelerate smoothly to the
final end point without overshoot. When traveling in one direction, if a new position advancement value
requires the wheel to reverse direction, it will still decelerate smoothly to a stop at the user-set ramp rate
before re-accelerating in the opposite direction toward the new end point.
The main microcontroller communicates easily with up to four Position Controllers over a single-wire
universal asynchronous serial receiver and transmitter (UART) bus. The UART operates at 19.2 kbits/sec
data rate, 8-bit frame, 1 stop bit, no parity.
bus is electrically connected. In most cases, the data line on the Position Controller can be directly
connected to the main microcontroller with no additional external components required.
Setting the Device ID
When more than one device is connected on the same bus, it is necessary to give each device a unique
device ID. Each device’s ID value is physically set by its corresponding jumper configuration read when
powered on (see table below). Notice that the possible values are 1 through 4. Commands can address
ID 0 as a special case address to send commands to all devices at once. Devices are shipped with both
jumpers installed (ID value 1).
Copyright © Parallax Inc.
Start
Distance (in positions)
Maximum Speed Value (SMAX)
Number of positions to travel (TRVL)
Speed Ramp Rate (SSRR)
* ID Value 0 is reserved for addressing all
devices at once.
A|B
Position Controller Kit (#27906)
See the Module Schematic section for details on how the
ID Value*
1
2
3
4
Binary
001
010
011
100
Point
End
v1.1 3/22/2010 Page 4 of 13
Figure 3
Typical speed profile for
traveling a certain
distance. The set point is
advanced incrementally
until it reaches the
endpoint.