Innovation First, Inc.
EDU-RC & Motherboard Reference Guide
11.8.2002
www.InnovationFirst.com
Page 12
15. Write Protect Jumper
The Write Protect jumper on the Isaac16 EDU Motherboard is used to allow or disallow writing to the
PBASIC program memory chip. The PBASIC program memory chip is located on the bottom side of
the Motherboard.
The PBASIC program can be changed when the jumper is installed (Write Protect OFF).
The PBASIC program
cannot
be changed when the jumper is
not
installed (Write Protect ON).
16. Oscillator Output
The oscillator output is set by default to output a 40 KHz signal at about a 50% duty cycle. This
frequency can be controlled by the 17
th
PWM byte in the SEROUT command in the PBASIC code. As
the 17
th
byte varies from 2 – 254, the OSC Output frequency will vary from 19.6 KHz to 1.66 MHz.
The 17
th
byte only needs to be sent out 1 time to set the frequency. The 17
th
byte does not need to be
sent out again until the frequency needs to be changed. The OSC Output port also has a Ground and
Power pin. The Ground pin is the left pin of OSC Output port and marked “BLK” on the EDU
Motherboard. The power pin is the center pin and will supply Battery voltage. The OSC Output is the
left pin.
The formula for the frequency is:
1/((PWM value + 1) * 4 * 0.00000005) Valid PWM value range: 2 – 254.
Caution: The center pin on the OSC Output port is connected to the Battery input voltage.
Depending on your battery, this voltage may be too high for some devices and they may be
damaged.