70009 Parallax Inc, 70009 Datasheet - Page 82

• Manufacturer Part Number: 70009
• Description: BOOK UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc
• Type: Signal Analysisr

Specifications of 70009

• Style: Book
• Title: Understanding Signals
• Contents: Guide to Generate, View and Measure Wave Forms
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Other names: 70009PAR

Did you notice that when the transmitter is sending bit 0 it should be high or logic 1?
This is because RS-232 is inverted. In a lot of cases it is also level shifted to -12 V for
logic 1 and +12 V for logic 0. This helps transmit the data across long serial cables.
Although, you can simply send a 5 V TTL signal from the BASIC Stamp and have good
results with most computers. Since RS-232 signals come in both polarities, it’s a good
thing we have the OPTAscope to “see” this polarity rather than trying to guess it.
ACTIVITY #1: DISPLAYING 8-BIT INVERTED DATA
In this activity the BASIC Stamp will send the numbers 1 to 1,000 to the Debug Terminal
and the OPTAscope will display them as they are received.
Required Parts
(2) Jumper wires
Building the Asynchronous Serial Circuit
This simple circuit is built the same way for the Board of Education and HomeWork
Board.
√
√
√
Build the circuit as shown in Figure 6-2 and Figure 6-3
Connect the CH1 probe to P14 of the BASIC Stamp.
Connect the Ground probe to the BASIC Stamp’s Vss.
P14
Vss
OPTA
OPTA
scope
scope
CH1
GND
Figure 6-2:
High and low signals
circuit schematic