VSC838-01
Datasheet
Serial Read-Back
Read-back of the program memory contents is accomplished in serial mode by setting the ALE_SCN pin HIGH. This
will serially shift out the contents of the main latches in the program memories, slice 36 first and slice 0 last, and
MSB-first, LSB-last for each 7-bit word (for more information, see
INCHAN[1](SCLK) with ALE_SCN=0 and SERIAL=1 must occur to load the entire 483-bit shift register prior to
shifting out data. At a clock rate of 66MHz, this operation takes 7.26µs.
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Activity Monitoring
The activity monitor observes the output of the internal 37
th
output from the core. By programming the 37
th
output to
observe various inputs, the input signals can be scanned for activity or lack thereof. Each rising edge of ACTCLK
causes the monitor to read out the activity state from the previous ACTCLK period and clears the internal activity
state until a data transition triggers it again. There must be a minimum of one rising and one falling edge on the
observed input data pin during the ACTCLK period for activity to be detected. After power-on the output of
ACTIVITY after the first ACTCLK rising edge is unknown.
To program the activity channel, ACTCHAN must be set HIGH and OUTCHAN[5:0] must be set to 100000. Set
INCHAN[5:0] to the desired input channel to be monitored. For all other programming operations, ACTCHAN must
be LOW.
Selective Power-Down
Unused input and output channels can be made to consume little or no power via one of two methods of selective
power-down.
Software Power-Down
Using this feature, unused outputs may be disabled, saving approximately 150 mW per output channel for maximum
dissipation conditions. This is accomplished by programming each unused output to look at input 63 (3F Hex), which
represents a non-existent input channel. The channel may be subsequently activated by programming a valid input
address. It is recommended, however, that any changes in power programming only be executed as part of an
initialization sequence to guard against the effects of any switching transients that might result from changing the
power supply current suddenly. Software mode does not affect the functioning or power of unused input channels.
Hardware Power-Down
Using this feature, the power associated with given input channel pairs may be shut off by tying the corresponding
V
EE
pin to V
CC
(for more information, see
manner. Approximately 150 mW per input channel pairs is saved under the maximum dissipation conditions. The
power associated with given output channel pairs, including their contribution to the core power, can be shut off by
tying the corresponding V
EE
pin to V
CC
(for more information, see
two output channels is saved under the maximum dissipation conditions.
Certain V
EE
pins must always be active. In other words, tied to the most negative supply, so the corresponding inputs
and outputs will always be on and consuming power. For more information about the location of these pins, see
4 of 19
VMDS-10195 Revision 4.0
August 19, 2005
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
