Dicon VX500, Руководство по эксплуатации, Страница: 16 / 24

91500 Revision B
16 DiCon Fiberoptics VX500 Fiberoptic Switch
Calculating Switching Time
The time period that begins at the falling edge of the STROBE signal and ends upon com-
pletion of the switching operation can be divided into three constituent periods. The first
period begins when STROBE goes low and ends when BUSY goes high. During this period
(500ns max.), the optical connection for the previous channel selection remains valid.
The second period begins when BUSY goes high and the switch armature begins to move.
It ends when the armature reaches the specified output channel. The period lasts for 16ms
per switched channel, including blocked and duplex channels. During this period, optical out-
put is invalid; optical noise may appear on various output channels as the armature rotates.
The final period is called the debounce period. It ends when the armature is steady, the
switch has established a valid optical connection, and BUSY goes low. The debounce
period lasts for 300ms.
1
Switching time is the sum of final two periods. For example, consider the calculation of total
switching time for the following two scenarios:
Switch From Channel 15 To Channel 1 (Simplex 1
×
N Switch)
(14
×
16 ms) + 300 ms = 524 ms
Switch From Channel 2 To Channel 6 (2
×
N Blocking Switch)
(8
×
16 ms) + 300 ms = 428 ms
Additionally, there are two special cases for calculating switching time. First, if a STROBE
pulse is applied with no change in the latched value of the channel address (<D4:D0>), the
BUSY line will go high for 60–80ms. Second, if a reset instruction is given twice in a row,
the BUSY line will go high for 410ms max. For example, consider the total switching time
for the following two scenarios:
Switch From Channel 3 To Channel 3
60– 80ms
Switch From Channel 0 To Channel 0
410 ms max.
Table 6: VX500 Timing Parameters
Parameter Description Min. Max. Units
Tsu Setup time. The channel address (<D4:D0>) and
RESET inputs must remain stable preceding the
falling edge of STROBE. 100 — ns
Th Hold time. The channel address (<D4:D0>) and
RESET inputs must remain stable following the
falling edge of STROBE. 150 — ns
Tstb
STROBE pulse width.
a 150
6
×
10
7 ns
Tbsy STROBE low to BUSY high. During this period the
switch maintains a valid connection to the previous
output channel. — 500 ns
Tsw Switching time. During this period there may be
invalid optical transmission on all channels. — 300 +
(16
×
N)
ms
Tpwr Power-up delay. The switch may lock up if TTL-level
signals are applied to the data inputs during this
period. Status and optical outputs are unreliable. — 970 ms
a. DiCon recommends a low pulse width of 1
µ
sec to 10
µ
s.
1. The BUSY line will remain high until the end of the STROBE pulse, even if the switch operation is complete
and the optical connection is stable.