OXCB950
OXFORD SEMICONDUCTOR LTD.
reset is hi-impedance. As the circuitry is disabled, the
transistor connected to the CCLKRUN# line is off and so
the state of the CCLKRUN# signal pin is controlled by the
host, which will be holding the pin in the asserted state
(clock running) as the inserted device needs to be
enumerated and configured. When the operating system
hands control to the custom device driver, the device driver
will assigned a logic '1' to the pin MIO0 to enable the clock
control circuitry which will begin to monitor the status of the
CCLKRUN# line.
When the host intends on stopping the clock, it negates the
CCLKRUN# line by synchronously driving the CCLKRUN#
line to logic '1' and then releasing its drive to this line. This
will also result in the CCLKRUN# line being a logic '1' due
to the presence of a pull-up on the host end of the
interface.
When the clock control circuitry has sampled the negation
of the CCLKRUN# line for 2 samples, this results in the
open-collector transistor to be driven, thereby asserting the
CCLKRUN# line (this time by the target). In other words,
the clock control circuitry asserts the CCLKRUN# line 2
clocks after it had been negated by the host. This is the
required signalling to the host to prevent it from completing
its original intention of stopping the clock. The clock line
CCLK continues to run uninterrupted.
While the host continues to assert the CCLKRUN# line, to
indicate clock run, the clock control circuitry continuously
samples logic '0' that results in the open-collector transistor
being held in the off-state.
CCLK
CCLKRUN#
Q1
Q2/
transistor
drive
CCLK continues to run
Uninterrupted.
CLKRUN# driven
by host. Clock
control circuitry
contains all 0’s
Clock control
samples
thus keeping
transistor off
Clock control negates
drive to transistor, but
CCLKRUN# now held
asserted by the host
CCLKRUN#
negated for 1
clock cycle
Clock control samples
(during period transistor
CCLKRUN# negated
was driven)
for 2 clock cycles.
Host synchronously
Turns on transistor to
assert CCLKRUN# line.
negates CCLKRUN# to
indicate intention of
stopping clock.
OXCB950 DataSheet
MIS-0004 Jul 04 External-Free Release
Page 57
OXFORD [ OXFORD SEMICONDUCTOR ]
