7
Sharing a port
There are times when you need to split a
port into several sections, or where signals
on a port need to be shared between two or
more downstream E-blocks boards. In this
case you need to use a splitter cable. As an
example of this: supposing that you wanted
to develop a system that used two external
analogue sensors. The Sensor board only
has the capability for one external analogue
sensor, so you need to use a splitter
cable and the patch system to make the
appropriate connections. The splitter cable
allows you to connect one upstream port to
two downstream ports using IDC (Insulation
Displacement Connector) connectors and
ribbon cable. Here the link blocks on both
boards are in the ‘patch’ position. On the top
board the Analogue sensor is routed to bit
1, and on the bottom board the Analogue
sensor is routed to bit 2. This technique
allows you share ports between several
devices - this is particularly convenient for
communications systems where a device’s
serial port has to be shared.
Protecting E-blocks circuitry
Where possible leaded components have
been used for all devices on E-blocks boards
that can be subjected to electrical damage.
This means that in the case where devices on
the E-blocks boards do become damaged,
the task of replacing them is very simple.
Some upstream boards (ARM processor
boards and FPGA board) make use of surface
mounted technology components which can
not be socketed and which are not easy to
solder. In these cases we have used smaller
daughter boards so that if the key device
is broken then you can simply order a new
daughter board.
To protect upstream components, all
downstream E-blocks have been developed
with protective resistors so that it is not
possible to damage an upstream E-block by
improperly declaring an input as an output,
and having two output pins with different
output levels clash.
However there are circumstances where it
will still be possible to electrically damage
your E-blocks:
•
When using screw terminal connectors
turn power off when routing power wires.
•
When connecting two upstream boards
together with a gender changer or IDC
cable then you are connecting one output
to another. It is strongly recommended that
you use protective resistors for the lines you
need to connect to prevent chip damage.
•
Although modern chips are less prone to
static damage these days, you are advised
to make sure you are earthed before
handling E-blocks circuit boards. If you have
not got access to an antistatic wristband
then quickly touching a radiator or other
earthed device will minimise the likelihood
of static damage.
•
When using a patch or prototype board you
have the opportunity to connect external
components directly to the pin of the micro
controller or CPLD device. This also means
that you have the opportunity to short
circuit the device to 0V or +V.