279
Programmable Hardware Manual (PHM)
© Tibbo Technology Inc.
As an example, consider Tibbit
(DAC, shown above). This Tibbit is based on the
MCP4728 IC from Microchip. It communicates with the main CPU via the I2C
interface lines SCL and SDA. There are also two additional interface lines LDAC and
BUSY. LED colors are:
·
SCL: this is the clock line of the I2C interface. Red LED is used because this line is
an output.
·
SDA: this is the data line of the I2C interface. Yellow LED is used because the
data line is bi-directional.
·
LOAD: this is the control line manipulated by the CPU. Hence, the LED color is red.
·
BUSY: this is the status line from the DAC IC. Hence, the LED color is green.
The same logic applies to "power good" LEDs. If the LED is on the power line that
provides power to the main CPU/board (power flowing in) then the color of this LED
will be green. If this is the power line that takes power from the main CPU/board
(power flowing out) then the color of this LED will be red.
Example: Tibbit
(+/-15V power supply). This Tibbit takes power from the +5V
supply rail and generates voltages for +15V and -15V power rails. Four LED
indicators on the module are:
·
5V power good -- the LED is red because this power is provided by (is flowing out
of) the system.
·
SDWN -- the LED is red because this is a shutdown line that is controlled by the
main CPU.
·
+15V and -15V -- these LEDs are green because the Tibbit provides the
corresponding voltages to the board (+15V and -15V power is flowing into the
board).