9. Resets, Clocks and Power-up Options
169
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
PowerSpan II’s response to the assertion of a bidirectional reset pin is independent of the direction of
that pin.
PowerSpan II’s PB_RST_, P1_RST# and P2_RST# are bidirectional. When they are configured as
outputs, they still sense logic lows. If any of these signals sense the logic low on their particular reset
signal, the corresponding PowerSpan II bus interface is in a reset state. However, the reset does not
propagate to other PowerSpan II busses when the reset pin is configured as an input. In order for
PowerSpan II to propagate the reset another bus, the reset pin must be configured as an input (see
“Reset Generation” on page 169
)
PowerSpan II’s input reset pins do not require clock synchronization - they are asynchronous.
The Phase Locked Loops (PLLs) in PowerSpan II are only reset by either the assertion of PO_RST_ or
negation of HEALTHY#. The assertion of PO_RST_ or negation of HEALTHY# causes all the
PowerSpan II resources to be reset. These resources are not released from reset until all PLLs are
locked (see
and
, parameter
t
103
).
The HEALTHY# pin tristates all of PowerSpan II’s output buffers, and inhibits all of PowerSpan II’s
input buffers. See
“CompactPCI Hot Swap Silicon Support” on page 53
for more details on the use of
HEALTHY#.
The assertion of TRST_ resets the JTAG controller and configures the Boundary Scan Register for
normal system operation.
9.1.1.3
Reset Generation
Each of PowerSpan II’s three interfaces have bidirectional reset pins that are used to reset the hardware
on the associated bus.
PowerSpan II assertion of PB_RST_ occurs if PB_RST_DIR is pulled high and one of the following
occurs:
•
PO_RST_ asserted
•
P1_RST_DIR is pulled low and P1_RST# is asserted
•
P2_RST_DIR is pulled low and P2_RST# is asserted
PowerSpan II assertion of P1_RST# occurs if P1_RST_DIR is pulled high and on of the following
occurs:
•
PO_RST_ asserted
•
PB_RST_DIR is pulled low and PB_RST# is asserted
•
P2_RST_DIR is pulled low and P2_RST# is asserted
Applications that use both HEALTHY# and PO_RST_ must assert HEALTHY# before
negating PO_RST_. (see
, parameter
t
101
)
Customers must assert TRST_ concurrently with PO_RST_ as part of the power-up reset
sequence. If the PowerSpan II JTAG interface is not used, the TRST_ signal must be
pulled-down with a 1 Kohm resistor.