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SECTION 4
FUNCTIONALITY
This section describes the main functions of the MPC821FADS daughterboard.
• Reset
• Interrupts
• Clock generator
• LCD panel support
• Board control and status registers
4.1 RESET
There are three sources of reset for the MPC821 microprocessor:
• Power-on reset
• Hard reset
• Soft reset
4.1.1 Power-On Reset
On the MPC821FADS daughterboard, a power-on reset can be generated from a keep-alive
power bus or a main power bus. The J1 jumper is used to select one of these sources. When
you select the keep-alive power source, a dedicated voltage detector made by Seiko
(S-8051HN-CD-X), which has a detection voltage range of 1.795–2.005V, generates the
power-on reset. During a keep-alive power-on, or when there is a voltage drop of that input
into the above range, a power-on reset is generated (the PORESET input of the MPC821 is
asserted for approximately 4 seconds).
When you select the main power source, a dedicated voltage detector made by Seiko
(S-8052ANY-NH-X), with a detection voltage range of 2.595–2.805V, generates the
power-on reset. During a main 3.3V bus power-on, or when there is a voltage drop of that
input into the above range, a power-on reset is generated (the PORESET input of the
MPC821 is asserted for approximately 4 seconds). The main power-on reset also generates
a power-on reset to all logic on the motherboard.
The power-on reset configuration is read by the MPC821 when PORESET is asserted to the
MPC821. See Section 4.1.6.1 Power-On Reset Configuration of the MPC8xxFADS
User's Manual for more information.
MOTOROLA
MPC821FADS-DB USER'S MANUAL
4-1
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