28123 Parallax Inc, 28123 Datasheet - Page 326

• Manufacturer Part Number: 28123
• Description: TEXT WHAT'S A MICROCONTROLLER
• Manufacturer: Parallax Inc
• Type: Programmingr

Specifications of 28123

• Style: Book
• Title: What's a Microcontroller?
• Contents: Whats a Microcontroller? Text
• Product: Microcontroller Accessories
• Core Processor: PIC16C57c
• Flash: 128 Bytes
• Operating Supply Voltage: 9 V
• Board Size: 31 mm x 16 mm
• Lead Free Status / RoHS Status: Not applicable / Not applicable

The rules have to do with how much current an I/O pin is allowed to deliver and how
much current a group of I/O pins is allowed to deliver.
If you know how to calculate how much current your circuit will use, then you can decide
if it’s OK to make your LEDs glow that brightly. Every electronic component has rules
for what it does with voltage, resistance, and current. For the light emitting diode, the
rule is a value called the diode forward voltage. For the resistor, the rule is called Ohm’s
Law. You need to figure out how much current your LED circuit is using. There are also
rules for how current and voltage add up in circuits. These are called Kirchoff’s Voltage
and Current Laws.
Current Rules for BASIC Stamp I/O Pins
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An I/O pin can “source” 20 mA. In other words, if you send the HIGH signal to an
I/O pin, it should not supply the LED circuit with more than 20 mA.
If you rewire the LED circuit so that the BASIC Stamp makes the LED turn on
when you send the LOW command, an I/O pin can “sink” up to 25 mA.
P0 through P7 can only source up to 20 mA. Likewise with P8 through P15. If
you have lots of LED circuits, you will need larger resistors so that you don’t draw
too much current.