6.5. Specification and connection examples
This chapter contains certain major features for external circuits connecting to module
E20-
10
.
6.5.1. Connections to USB
The following features shall be taken into account:
•
Speed of 20 MB/s (corresponds to data acquisition frequency of 10 MHz at zero
interframe delay) is close to maximum operational speed
high-speed
USB 2.0 interface. In
particular, it means, that both
E20-10
connected to one USB-hub (or one USB-controller
of the computer) can operate up to 10 MB/s each only.
•
On the one hand, modern USB3.0 – hubs shall provide speed of 20 MB/s for each
downstream port, on the other hand, hub's manufacturers are not obliged to provide such
speed and in the pursuit of the product cheapening the versions
…are possible.
•
Under combined connecting
high-speed
and
full-speed
USB devices to the same USB-hub
the speed of USВ will be set based on the slowest device, i.e.
full-speed
only.
•
At speed
full-speed
(USB 1.1) the maximum achievable speed of data transmission
E20-
10 —
1 MB/s (ADC 500 kHz), it can be set via corresponding setting of interframe delay.
At higher frequencies FIFO buffer of
E20-10
will be overflowed, because USB
full-speed
bandwidth capacity will not provide the required speed of spooling from
E20-10
(buffer
overflow will lead to data loss but not to service outage of E20-10).
•
When several
E20-10
are used at speed of more than 10 MB/s it is recommended to
connect them to
computer different controllers
– in this case, there should be no
bandwidth capacity problems (otherwise, internal USB-hub on mother card will not
provide 20 MB/s for each port).
If required, you can use additional PCI or PCI Express
expansion cards for USB-ports in auxiliary USB-controllers on the basis: 1 card for 1
module E20-10 (the required speed will be practically provided via USB).
•
It should be noted, that when using several modules E20-10 at maximum speed with one
computer there are objective physical limits for: - physical recording speed on hard disk
(if your software uses such recording); - chipset operation speed via computer RAM,
because data transmission from E20-10 to computer RAM is via DMA (i.e. with computer
processor partial involvement); - computing load with exterior tasks actively working with
RAM.
•
Maximum length of USB cable according to standard - 5 m.
Attention!
To avoid
E20-10
failures (particularly, at high operation speeds) it is highly
recommended not to use the computer remote USB expansion ports to connect
E20-10
(these are the ports that use pin double-row connectors
on mother cards with extension
cables and additional USB connectors, which are usually located either at the rear of the
system block on additional bars or moved forward of the computer case) due to the lack of
quality of these connections for a high-speed device like
E20-10
on several important
16
L-Card can not warrant third-party product quality; prior to buy the selected hub it is necessary to be clear maximum
speeds on downstream-ports.
17
in general, such USB connector is not even specified in USB specifications 1.1, 2.0 and 3.0 [10] [11]