Calibre UK IC Communication Adapter ICA93LV User Manual - page 5
Revision 1.7
Page 4 of 27
09/12/1999
3.
Connecting the Adapter to your System
3.1.
Connector Pinout
All external connections are made via a 9 way “D” socket:
Pin
Normal Mode
1
0V
2
0V
3
0V
4
0V
5
NC
6
SDA (Bi-directional)
7
+V Variable bus voltage
8
SCL (Bi-directional)
9
NC
NOTE:
THE PINS MARKED NC MUST NOT BE CONNECTED IN NORMAL MODE.
3.2.
Normal/Long Distance Mode
The ICA93 does NOT support the 4-wire long distance mode which the 5V only ICA90 model can operate
in. This is the only incompatibility between the two models.
3.3.
Bus Capacitance Limitations/Cable Choice
The maximum allowable capacitance on the I
2
C bus in normal mode depends on the value of the SCL
and SDA master pull-ups, but never exceeds 400pF. Refer to Phillips Technical Handbook Book 4 Parts
12a and 12b for further details (see Section 8 - Further Information for references). Care should be taken
in choosing a length and type of interconnecting cable, which will not exceed this limit.
For most systems with a distance of a few metres between the I
2
C Communications Adapter and the
target system, screened cable is NOT recommended, as it is likely to introduce too much capacitance.
However, the EMC performance of an unscreened cable is always potentially poorer than a screened
one. The Adapter's EMC performance even with an unscreened cable is good - but this may not be true
of the target system! If you are in any doubt at to the best way to connect up your system with EMC in
mind please contact your supplier or Calibre for advice.
3.4.
Variable Voltage Bus Power Supply
Pin 7 on the “D” connector is connected to the variable bus voltage power rail. Power for external circuitry
can be drawn from here, but care should be taken never to short it to 0V or to exceed 250mA loading. It is
short circuit and overload protected by a self-resetting thermal fuse but prolonged shorting could cause
the ICA93 to generate an excessive amount of heat inside your computer.
When shipped to you, the bus voltage was pre-set at 3.3V for use with low voltage memories. You can
adjust the voltage between 2V and 6V by inserting a small screwdriver through the hole in the card
mounting bracket. As you adjust the voltage (you can monitor it by connecting a meter to pin 7 of the bus
connector) the bus logic levels will track, keeping at 30% / 70% of supply for low and high level thresholds
respectively.
The Links 6, 7, and 8 are factory set to VAR and MUST NOT BE MOVED.
Your ICA93 has been factory set for use on 3.3V I
2
C bus systems. Use on 5V I
2
C bus systems
without adjusting the voltage control WILL CAUSE PERMANENT DAMAGE to the IC93. The fault is
factory detectable and you WILL BE CHARGED FOR THE REPAIR.