
93
Programmable Hardware Manual (PHM)
© Tibbo Technology Inc.
Further information on status LEDs can be found in
4.6.1.7
Power, Reset, and Mode Selection Lines
The EM1202 should be powered from a stabilized DC power supply with nominal
output voltage of 3.3V (+/- 5% tolerance). Current consumption of the EM1202 is
approximately 230mA (PLL on, 100BaseT mode). Providing an adequate power supply
is very important -- poorly built circuit may affect EM1000 operation. We
recommend that you use a switching power supply. One (but not the only) example
of such circuit is shown below.
Proper external reset is not required. The EM1202 has a reliable power-on reset
circuit with brown-out detection. Optionally, you can connect a reset button or
some other reset-generating circuit to the RST pin of the EM1202. This will allow
you to generate "external" resets. The RST line has active HIGH polarity. If you are
not using the RST pin you can leave it unconnected.
The main clock frequency of the EM1202 is generated by an 11.0592MHz crystal
connected to the onboard PLL circuit. When the PLL is off, the EM1202 is clocked at
11.0592MHz. When the PLL is on, the main clock is eight times higher- 88.4736MHz.
Naturally, with PLL on the EM1202 works 8 times faster and consumers more current
(230mA with PLL on against 110mA with PLL off). Main clock frequency also affects
the baudrates of
when in the UART mode, as well as the frequency
produced by the
The PLL cannot be switched off and on while the EM1202 is running. This is because
when PLL mode changes its output needs some time to stabilize. For this reason,
the PLL mode of the EM1202 can only be changed on reset. A special internal delay
circuit will hold the EM1202 in reset while PLL frequency stabilizes.
Unlike the
, the EM1202 does not have a hardware pin to control the state
of the PLL. On power up, the PLL is always enabled. Your Tibbo BASIC/C application
can change the PLL mode programmatically. The application can check the current
PLL mode through the system (sys.) object (see TIDE, TiOS, Tibbo BASIC, and
Tibbo C Manual). If the PLL mode needs to be changed, the application can set new
mode and then perform an internal reset (again, through the system object). The
internal reset is identical to the power-on or external reset with one difference: the
PLL mode will not default to "PLL on" but instead will be set as requested by the
application prior to the reset.
The function of the MD line is described in
.
Power supply circuit
Many power supply circuits will work well. The one below is being used by Tibbo.
The circuit can handle input voltages in the 9-24V range.