28301 Parallax Inc, 28301 Datasheet - Page 5

• Manufacturer Part Number: 28301
• Description: DAUGHTERBOARD 3PIN I/O MOBO
• Manufacturer: Parallax Inc

Specifications of 28301

• Accessory Type: Daughter Board, Power and I/O Interface
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: MoBoStamp, MoBoProp
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Serial devices can communicate directly with the BASIC Stamp on headers A2, A3, P8, and P9. They can
communicate with the AVR on headers A0, A1, A2, and A3, but to do so requires the appropriate AVR
firmware to be loaded.
Analog Input
Analog voltage levels can be coupled to A0 and A1 to be measured by the AVRs on MoBoStamp boards.
This function is included in the GPIO-3 coprocessor firmware preinstalled in the MoBoStamp
motherboard. Analog readings are referred either to the AVR’s Vdd or to its internal 1.1V reference. This
has some consequences for both accuracy and component safety, depending on how the mother- and
daughterboard’s power select jumpers are set. There are two measures of accuracy: 1) Absolute, which
refers to the ability to determine a specific voltage, and 2) Ratiometric, which determines the ability to
measure a voltage as a percentage of the device header’s 5V supply (source ref). The following table
approximates these relationships for the MoBoStamp. Other contributory factors will include further
down-regulation of the source reference and electrical noise.
© Parallax, Inc. • PWR-I/O-DB (2006.09.13)
Important: Serial devices which communicate back to the BASIC Stamp, AVR, or Propeller will likely
do so with a 5V signal level for “high”. For this reason, it is important to set Vdd on the MoBoStamp
motherboard to 5V or to use a current-limiting resistor (4.7K for A0-A2, 1.2K for P8-P9) in series with
the white signal wire. When interfacing to the MoBoProp motherboard, use 2.2K current-limiting
resistors.
DB 5V MB
Vin J1
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