VITESSE
SEMICONDUCTOR CORPORATION
3.2Gb/s
36x37 Crosspoint Switch
Preliminary Data Sheet
VSC838
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 (see Figure 3). One rising edge of 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 7.26
µ
s.
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 access the 37
th
output, ACTCHAN and INCHAN[5] must both be HIGH.
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 170 mW per channel for maxi-
mum dissipation conditions. This is accomplished by programming each unused output to look at input 127 (7F
Hex), which represents a non-existent input channel. The channel may be subsequently activated by program-
ming a valid input address. It is recommended, however, that any changes in power programming only be exe-
cuted 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 pairs of inputs may be shut off by tying the correspond-
ing V
EE
pin to V
CC
(see Table 10). Approximately 160 mW per input pair is saved under the maximum dissipa-
tion conditions. The power associated with given pairs of outputs, including their contribution to the core
power, can be shut off by tying the corresponding V
EE
pin to V
CC
(see Table 10). Approximately 360 mW per
output pair 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 correspond-
ing inputs and outputs will always be on and consuming power. See Figure 7 and Table 10 for the location of
these pins.
Page 4
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
G52351-0, Rev 3.0
02/12/01
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
